mm/huge_memory.c

   1 /*
   2  *  Copyright (C) 2009  Red Hat, Inc.
   3  *
   4  *  This work is licensed under the terms of the GNU GPL, version 2. See
   5  *  the COPYING file in the top-level directory.
   6  */
   7
   8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   9
  10 #include <linux/mm.h>
  11 #include <linux/sched.h>
  12 #include <linux/highmem.h>
  13 #include <linux/hugetlb.h>
  14 #include <linux/mmu_notifier.h>
  15 #include <linux/rmap.h>
  16 #include <linux/swap.h>
  17 #include <linux/shrinker.h>
  18 #include <linux/mm_inline.h>
  19 #include <linux/kthread.h>
  20 #include <linux/khugepaged.h>
  21 #include <linux/freezer.h>
  22 #include <linux/mman.h>
  23 #include <linux/pagemap.h>
  24 #include <linux/migrate.h>
  25 #include <linux/hashtable.h>
  26
  27 #include <asm/tlb.h>
  28 #include <asm/pgalloc.h>
  29 #include "internal.h"
  30
  31 /*
  32  * By default transparent hugepage support is disabled in order that avoid
  33  * to risk increase the memory footprint of applications without a guaranteed
  34  * benefit. When transparent hugepage support is enabled, is for all mappings,
  35  * and khugepaged scans all mappings.
  36  * Defrag is invoked by khugepaged hugepage allocations and by page faults
  37  * for all hugepage allocations.
  38  */
  39 unsigned long transparent_hugepage_flags __read_mostly =
  40 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
  41         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
  42 #endif
  43 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
  44         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
  45 #endif
  46         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
  47         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
  48         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
  49
  50 /* default scan 8*512 pte (or vmas) every 30 second */
  51 static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
  52 static unsigned int khugepaged_pages_collapsed;
  53 static unsigned int khugepaged_full_scans;
  54 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  55 /* during fragmentation poll the hugepage allocator once every minute */
  56 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  57 static struct task_struct *khugepaged_thread __read_mostly;
  58 static DEFINE_MUTEX(khugepaged_mutex);
  59 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  60 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  61 /*
  62  * default collapse hugepages if there is at least one pte mapped like
  63  * it would have happened if the vma was large enough during page
  64  * fault.
  65  */
  66 static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
  67
  68 static int khugepaged(void *none);
  69 static int khugepaged_slab_init(void);
  70
  71 #define MM_SLOTS_HASH_BITS 10
  72 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  73
  74 static struct kmem_cache *mm_slot_cache __read_mostly;
  75
  76 /**
  77  * struct mm_slot - hash lookup from mm to mm_slot
  78  * @hash: hash collision list
  79  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  80  * @mm: the mm that this information is valid for
  81  */
  82 struct mm_slot {
  83         struct hlist_node hash;
  84         struct list_head mm_node;
  85         struct mm_struct *mm;
  86 };
  87
  88 /**
  89  * struct khugepaged_scan - cursor for scanning
  90  * @mm_head: the head of the mm list to scan
  91  * @mm_slot: the current mm_slot we are scanning
  92  * @address: the next address inside that to be scanned
  93  *
  94  * There is only the one khugepaged_scan instance of this cursor structure.
  95  */
  96 struct khugepaged_scan {
  97         struct list_head mm_head;
  98         struct mm_slot *mm_slot;
  99         unsigned long address;
 100 };
 101 static struct khugepaged_scan khugepaged_scan = {
 102         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 103 };
 104
 105
 106 static int set_recommended_min_free_kbytes(void)
 107 {
 108         struct zone *zone;
 109         int nr_zones = 0;
 110         unsigned long recommended_min;
 111
 112         if (!khugepaged_enabled())
 113                 return 0;
 114
 115         for_each_populated_zone(zone)
 116                 nr_zones++;
 117
 118         /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
 119         recommended_min = pageblock_nr_pages * nr_zones * 2;
 120
 121         /*
 122          * Make sure that on average at least two pageblocks are almost free
 123          * of another type, one for a migratetype to fall back to and a
 124          * second to avoid subsequent fallbacks of other types There are 3
 125          * MIGRATE_TYPES we care about.
 126          */
 127         recommended_min += pageblock_nr_pages * nr_zones *
 128                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
 129
 130         /* don't ever allow to reserve more than 5% of the lowmem */
 131         recommended_min = min(recommended_min,
 132                               (unsigned long) nr_free_buffer_pages() / 20);
 133         recommended_min <<= (PAGE_SHIFT-10);
 134
 135         if (recommended_min > min_free_kbytes) {
 136                 if (user_min_free_kbytes >= 0)
 137                         pr_info("raising min_free_kbytes from %d to %lu "
 138                                 "to help transparent hugepage allocations\n",
 139                                 min_free_kbytes, recommended_min);
 140
 141                 min_free_kbytes = recommended_min;
 142         }
 143         setup_per_zone_wmarks();
 144         return 0;
 145 }
 146 late_initcall(set_recommended_min_free_kbytes);
 147
 148 static int start_khugepaged(void)
 149 {
 150         int err = 0;
 151         if (khugepaged_enabled()) {
 152                 if (!khugepaged_thread)
 153                         khugepaged_thread = kthread_run(khugepaged, NULL,
 154                                                         "khugepaged");
 155                 if (unlikely(IS_ERR(khugepaged_thread))) {
 156                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
 157                         err = PTR_ERR(khugepaged_thread);
 158                         khugepaged_thread = NULL;
 159                 }
 160
 161                 if (!list_empty(&khugepaged_scan.mm_head))
 162                         wake_up_interruptible(&khugepaged_wait);
 163
 164                 set_recommended_min_free_kbytes();
 165         } else if (khugepaged_thread) {
 166                 kthread_stop(khugepaged_thread);
 167                 khugepaged_thread = NULL;
 168         }
 169
 170         return err;
 171 }
 172
 173 static atomic_t huge_zero_refcount;
 174 struct page *huge_zero_page __read_mostly;
 175
 176 static inline bool is_huge_zero_pmd(pmd_t pmd)
 177 {
 178         return is_huge_zero_page(pmd_page(pmd));
 179 }
 180
 181 static struct page *get_huge_zero_page(void)
 182 {
 183         struct page *zero_page;
 184 retry:
 185         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 186                 return ACCESS_ONCE(huge_zero_page);
 187
 188         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 189                         HPAGE_PMD_ORDER);
 190         if (!zero_page) {
 191                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 192                 return NULL;
 193         }
 194         count_vm_event(THP_ZERO_PAGE_ALLOC);
 195         preempt_disable();
 196         if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
 197                 preempt_enable();
 198                 __free_pages(zero_page, compound_order(zero_page));
 199                 goto retry;
 200         }
 201
 202         /* We take additional reference here. It will be put back by shrinker */
 203         atomic_set(&huge_zero_refcount, 2);
 204         preempt_enable();
 205         return ACCESS_ONCE(huge_zero_page);
 206 }
 207
 208 static void put_huge_zero_page(void)
 209 {
 210         /*
 211          * Counter should never go to zero here. Only shrinker can put
 212          * last reference.
 213          */
 214         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
 215 }
 216
 217 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
 218                                         struct shrink_control *sc)
 219 {
 220         /* we can free zero page only if last reference remains */
 221         return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
 222 }
 223
 224 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
 225                                        struct shrink_control *sc)
 226 {
 227         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
 228                 struct page *zero_page = xchg(&huge_zero_page, NULL);
 229                 BUG_ON(zero_page == NULL);
 230                 __free_pages(zero_page, compound_order(zero_page));
 231                 return HPAGE_PMD_NR;
 232         }
 233
 234         return 0;
 235 }
 236
 237 static struct shrinker huge_zero_page_shrinker = {
 238         .count_objects = shrink_huge_zero_page_count,
 239         .scan_objects = shrink_huge_zero_page_scan,
 240         .seeks = DEFAULT_SEEKS,
 241 };
 242
 243 #ifdef CONFIG_SYSFS
 244
 245 static ssize_t double_flag_show(struct kobject *kobj,
 246                                 struct kobj_attribute *attr, char *buf,
 247                                 enum transparent_hugepage_flag enabled,
 248                                 enum transparent_hugepage_flag req_madv)
 249 {
 250         if (test_bit(enabled, &transparent_hugepage_flags)) {
 251                 VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
 252                 return sprintf(buf, "[always] madvise never\n");
 253         } else if (test_bit(req_madv, &transparent_hugepage_flags))
 254                 return sprintf(buf, "always [madvise] never\n");
 255         else
 256                 return sprintf(buf, "always madvise [never]\n");
 257 }
 258 static ssize_t double_flag_store(struct kobject *kobj,
 259                                  struct kobj_attribute *attr,
 260                                  const char *buf, size_t count,
 261                                  enum transparent_hugepage_flag enabled,
 262                                  enum transparent_hugepage_flag req_madv)
 263 {
 264         if (!memcmp("always", buf,
 265                     min(sizeof("always")-1, count))) {
 266                 set_bit(enabled, &transparent_hugepage_flags);
 267                 clear_bit(req_madv, &transparent_hugepage_flags);
 268         } else if (!memcmp("madvise", buf,
 269                            min(sizeof("madvise")-1, count))) {
 270                 clear_bit(enabled, &transparent_hugepage_flags);
 271                 set_bit(req_madv, &transparent_hugepage_flags);
 272         } else if (!memcmp("never", buf,
 273                            min(sizeof("never")-1, count))) {
 274                 clear_bit(enabled, &transparent_hugepage_flags);
 275                 clear_bit(req_madv, &transparent_hugepage_flags);
 276         } else
 277                 return -EINVAL;
 278
 279         return count;
 280 }
 281
 282 static ssize_t enabled_show(struct kobject *kobj,
 283                             struct kobj_attribute *attr, char *buf)
 284 {
 285         return double_flag_show(kobj, attr, buf,
 286                                 TRANSPARENT_HUGEPAGE_FLAG,
 287                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 288 }
 289 static ssize_t enabled_store(struct kobject *kobj,
 290                              struct kobj_attribute *attr,
 291                              const char *buf, size_t count)
 292 {
 293         ssize_t ret;
 294
 295         ret = double_flag_store(kobj, attr, buf, count,
 296                                 TRANSPARENT_HUGEPAGE_FLAG,
 297                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 298
 299         if (ret > 0) {
 300                 int err;
 301
 302                 mutex_lock(&khugepaged_mutex);
 303                 err = start_khugepaged();
 304                 mutex_unlock(&khugepaged_mutex);
 305
 306                 if (err)
 307                         ret = err;
 308         }
 309
 310         return ret;
 311 }
 312 static struct kobj_attribute enabled_attr =
 313         __ATTR(enabled, 0644, enabled_show, enabled_store);
 314
 315 static ssize_t single_flag_show(struct kobject *kobj,
 316                                 struct kobj_attribute *attr, char *buf,
 317                                 enum transparent_hugepage_flag flag)
 318 {
 319         return sprintf(buf, "%d\n",
 320                        !!test_bit(flag, &transparent_hugepage_flags));
 321 }
 322
 323 static ssize_t single_flag_store(struct kobject *kobj,
 324                                  struct kobj_attribute *attr,
 325                                  const char *buf, size_t count,
 326                                  enum transparent_hugepage_flag flag)
 327 {
 328         unsigned long value;
 329         int ret;
 330
 331         ret = kstrtoul(buf, 10, &value);
 332         if (ret < 0)
 333                 return ret;
 334         if (value > 1)
 335                 return -EINVAL;
 336
 337         if (value)
 338                 set_bit(flag, &transparent_hugepage_flags);
 339         else
 340                 clear_bit(flag, &transparent_hugepage_flags);
 341
 342         return count;
 343 }
 344
 345 /*
 346  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
 347  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
 348  * memory just to allocate one more hugepage.
 349  */
 350 static ssize_t defrag_show(struct kobject *kobj,
 351                            struct kobj_attribute *attr, char *buf)
 352 {
 353         return double_flag_show(kobj, attr, buf,
 354                                 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
 355                                 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 356 }
 357 static ssize_t defrag_store(struct kobject *kobj,
 358                             struct kobj_attribute *attr,
 359                             const char *buf, size_t count)
 360 {
 361         return double_flag_store(kobj, attr, buf, count,
 362                                  TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
 363                                  TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 364 }
 365 static struct kobj_attribute defrag_attr =
 366         __ATTR(defrag, 0644, defrag_show, defrag_store);
 367
 368 static ssize_t use_zero_page_show(struct kobject *kobj,
 369                 struct kobj_attribute *attr, char *buf)
 370 {
 371         return single_flag_show(kobj, attr, buf,
 372                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 373 }
 374 static ssize_t use_zero_page_store(struct kobject *kobj,
 375                 struct kobj_attribute *attr, const char *buf, size_t count)
 376 {
 377         return single_flag_store(kobj, attr, buf, count,
 378                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 379 }
 380 static struct kobj_attribute use_zero_page_attr =
 381         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
 382 #ifdef CONFIG_DEBUG_VM
 383 static ssize_t debug_cow_show(struct kobject *kobj,
 384                                 struct kobj_attribute *attr, char *buf)
 385 {
 386         return single_flag_show(kobj, attr, buf,
 387                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 388 }
 389 static ssize_t debug_cow_store(struct kobject *kobj,
 390                                struct kobj_attribute *attr,
 391                                const char *buf, size_t count)
 392 {
 393         return single_flag_store(kobj, attr, buf, count,
 394                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 395 }
 396 static struct kobj_attribute debug_cow_attr =
 397         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
 398 #endif /* CONFIG_DEBUG_VM */
 399
 400 static struct attribute *hugepage_attr[] = {
 401         &enabled_attr.attr,
 402         &defrag_attr.attr,
 403         &use_zero_page_attr.attr,
 404 #ifdef CONFIG_DEBUG_VM
 405         &debug_cow_attr.attr,
 406 #endif
 407         NULL,
 408 };
 409
 410 static struct attribute_group hugepage_attr_group = {
 411         .attrs = hugepage_attr,
 412 };
 413
 414 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 415                                          struct kobj_attribute *attr,
 416                                          char *buf)
 417 {
 418         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 419 }
 420
 421 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 422                                           struct kobj_attribute *attr,
 423                                           const char *buf, size_t count)
 424 {
 425         unsigned long msecs;
 426         int err;
 427
 428         err = kstrtoul(buf, 10, &msecs);
 429         if (err || msecs > UINT_MAX)
 430                 return -EINVAL;
 431
 432         khugepaged_scan_sleep_millisecs = msecs;
 433         wake_up_interruptible(&khugepaged_wait);
 434
 435         return count;
 436 }
 437 static struct kobj_attribute scan_sleep_millisecs_attr =
 438         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 439                scan_sleep_millisecs_store);
 440
 441 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 442                                           struct kobj_attribute *attr,
 443                                           char *buf)
 444 {
 445         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 446 }
 447
 448 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 449                                            struct kobj_attribute *attr,
 450                                            const char *buf, size_t count)
 451 {
 452         unsigned long msecs;
 453         int err;
 454
 455         err = kstrtoul(buf, 10, &msecs);
 456         if (err || msecs > UINT_MAX)
 457                 return -EINVAL;
 458
 459         khugepaged_alloc_sleep_millisecs = msecs;
 460         wake_up_interruptible(&khugepaged_wait);
 461
 462         return count;
 463 }
 464 static struct kobj_attribute alloc_sleep_millisecs_attr =
 465         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 466                alloc_sleep_millisecs_store);
 467
 468 static ssize_t pages_to_scan_show(struct kobject *kobj,
 469                                   struct kobj_attribute *attr,
 470                                   char *buf)
 471 {
 472         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 473 }
 474 static ssize_t pages_to_scan_store(struct kobject *kobj,
 475                                    struct kobj_attribute *attr,
 476                                    const char *buf, size_t count)
 477 {
 478         int err;
 479         unsigned long pages;
 480
 481         err = kstrtoul(buf, 10, &pages);
 482         if (err || !pages || pages > UINT_MAX)
 483                 return -EINVAL;
 484
 485         khugepaged_pages_to_scan = pages;
 486
 487         return count;
 488 }
 489 static struct kobj_attribute pages_to_scan_attr =
 490         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 491                pages_to_scan_store);
 492
 493 static ssize_t pages_collapsed_show(struct kobject *kobj,
 494                                     struct kobj_attribute *attr,
 495                                     char *buf)
 496 {
 497         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 498 }
 499 static struct kobj_attribute pages_collapsed_attr =
 500         __ATTR_RO(pages_collapsed);
 501
 502 static ssize_t full_scans_show(struct kobject *kobj,
 503                                struct kobj_attribute *attr,
 504                                char *buf)
 505 {
 506         return sprintf(buf, "%u\n", khugepaged_full_scans);
 507 }
 508 static struct kobj_attribute full_scans_attr =
 509         __ATTR_RO(full_scans);
 510
 511 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 512                                       struct kobj_attribute *attr, char *buf)
 513 {
 514         return single_flag_show(kobj, attr, buf,
 515                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 516 }
 517 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 518                                        struct kobj_attribute *attr,
 519                                        const char *buf, size_t count)
 520 {
 521         return single_flag_store(kobj, attr, buf, count,
 522                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 523 }
 524 static struct kobj_attribute khugepaged_defrag_attr =
 525         __ATTR(defrag, 0644, khugepaged_defrag_show,
 526                khugepaged_defrag_store);
 527
 528 /*
 529  * max_ptes_none controls if khugepaged should collapse hugepages over
 530  * any unmapped ptes in turn potentially increasing the memory
 531  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 532  * reduce the available free memory in the system as it
 533  * runs. Increasing max_ptes_none will instead potentially reduce the
 534  * free memory in the system during the khugepaged scan.
 535  */
 536 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 537                                              struct kobj_attribute *attr,
 538                                              char *buf)
 539 {
 540         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 541 }
 542 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 543                                               struct kobj_attribute *attr,
 544                                               const char *buf, size_t count)
 545 {
 546         int err;
 547         unsigned long max_ptes_none;
 548
 549         err = kstrtoul(buf, 10, &max_ptes_none);
 550         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 551                 return -EINVAL;
 552
 553         khugepaged_max_ptes_none = max_ptes_none;
 554
 555         return count;
 556 }
 557 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 558         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 559                khugepaged_max_ptes_none_store);
 560
 561 static struct attribute *khugepaged_attr[] = {
 562         &khugepaged_defrag_attr.attr,
 563         &khugepaged_max_ptes_none_attr.attr,
 564         &pages_to_scan_attr.attr,
 565         &pages_collapsed_attr.attr,
 566         &full_scans_attr.attr,
 567         &scan_sleep_millisecs_attr.attr,
 568         &alloc_sleep_millisecs_attr.attr,
 569         NULL,
 570 };
 571
 572 static struct attribute_group khugepaged_attr_group = {
 573         .attrs = khugepaged_attr,
 574         .name = "khugepaged",
 575 };
 576
 577 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 578 {
 579         int err;
 580
 581         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
 582         if (unlikely(!*hugepage_kobj)) {
 583                 pr_err("failed to create transparent hugepage kobject\n");
 584                 return -ENOMEM;
 585         }
 586
 587         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
 588         if (err) {
 589                 pr_err("failed to register transparent hugepage group\n");
 590                 goto delete_obj;
 591         }
 592
 593         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
 594         if (err) {
 595                 pr_err("failed to register transparent hugepage group\n");
 596                 goto remove_hp_group;
 597         }
 598
 599         return 0;
 600
 601 remove_hp_group:
 602         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
 603 delete_obj:
 604         kobject_put(*hugepage_kobj);
 605         return err;
 606 }
 607
 608 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 609 {
 610         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
 611         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
 612         kobject_put(hugepage_kobj);
 613 }
 614 #else
 615 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
 616 {
 617         return 0;
 618 }
 619
 620 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 621 {
 622 }
 623 #endif /* CONFIG_SYSFS */
 624
 625 static int __init hugepage_init(void)
 626 {
 627         int err;
 628         struct kobject *hugepage_kobj;
 629
 630         if (!has_transparent_hugepage()) {
 631                 transparent_hugepage_flags = 0;
 632                 return -EINVAL;
 633         }
 634
 635         err = hugepage_init_sysfs(&hugepage_kobj);
 636         if (err)
 637                 return err;
 638
 639         err = khugepaged_slab_init();
 640         if (err)
 641                 goto out;
 642
 643         register_shrinker(&huge_zero_page_shrinker);
 644
 645         /*
 646          * By default disable transparent hugepages on smaller systems,
 647          * where the extra memory used could hurt more than TLB overhead
 648          * is likely to save.  The admin can still enable it through /sys.
 649          */
 650         if (totalram_pages < (512 << (20 - PAGE_SHIFT)))
 651                 transparent_hugepage_flags = 0;
 652
 653         start_khugepaged();
 654
 655         return 0;
 656 out:
 657         hugepage_exit_sysfs(hugepage_kobj);
 658         return err;
 659 }
 660 subsys_initcall(hugepage_init);
 661
 662 static int __init setup_transparent_hugepage(char *str)
 663 {
 664         int ret = 0;
 665         if (!str)
 666                 goto out;
 667         if (!strcmp(str, "always")) {
 668                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
 669                         &transparent_hugepage_flags);
 670                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 671                           &transparent_hugepage_flags);
 672                 ret = 1;
 673         } else if (!strcmp(str, "madvise")) {
 674                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 675                           &transparent_hugepage_flags);
 676                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 677                         &transparent_hugepage_flags);
 678                 ret = 1;
 679         } else if (!strcmp(str, "never")) {
 680                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 681                           &transparent_hugepage_flags);
 682                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 683                           &transparent_hugepage_flags);
 684                 ret = 1;
 685         }
 686 out:
 687         if (!ret)
 688                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
 689         return ret;
 690 }
 691 __setup("transparent_hugepage=", setup_transparent_hugepage);
 692
 693 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 694 {
 695         if (likely(vma->vm_flags & VM_WRITE))
 696                 pmd = pmd_mkwrite(pmd);
 697         return pmd;
 698 }
 699
 700 static inline pmd_t mk_huge_pmd(struct page *page, pgprot_t prot)
 701 {
 702         pmd_t entry;
 703         entry = mk_pmd(page, prot);
 704         entry = pmd_mkhuge(entry);
 705         return entry;
 706 }
 707
 708 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
 709                                         struct vm_area_struct *vma,
 710                                         unsigned long haddr, pmd_t *pmd,
 711                                         struct page *page)
 712 {
 713         struct mem_cgroup *memcg;
 714         pgtable_t pgtable;
 715         spinlock_t *ptl;
 716
 717         VM_BUG_ON_PAGE(!PageCompound(page), page);
 718
 719         if (mem_cgroup_try_charge(page, mm, GFP_TRANSHUGE, &memcg))
 720                 return VM_FAULT_OOM;
 721
 722         pgtable = pte_alloc_one(mm, haddr);
 723         if (unlikely(!pgtable)) {
 724                 mem_cgroup_cancel_charge(page, memcg);
 725                 return VM_FAULT_OOM;
 726         }
 727
 728         clear_huge_page(page, haddr, HPAGE_PMD_NR);
 729         /*
 730          * The memory barrier inside __SetPageUptodate makes sure that
 731          * clear_huge_page writes become visible before the set_pmd_at()
 732          * write.
 733          */
 734         __SetPageUptodate(page);
 735
 736         ptl = pmd_lock(mm, pmd);
 737         if (unlikely(!pmd_none(*pmd))) {
 738                 spin_unlock(ptl);
 739                 mem_cgroup_cancel_charge(page, memcg);
 740                 put_page(page);
 741                 pte_free(mm, pgtable);
 742         } else {
 743                 pmd_t entry;
 744                 entry = mk_huge_pmd(page, vma->vm_page_prot);
 745                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 746                 page_add_new_anon_rmap(page, vma, haddr);
 747                 mem_cgroup_commit_charge(page, memcg, false);
 748                 lru_cache_add_active_or_unevictable(page, vma);
 749                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
 750                 set_pmd_at(mm, haddr, pmd, entry);
 751                 add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
 752                 atomic_long_inc(&mm->nr_ptes);
 753                 spin_unlock(ptl);
 754         }
 755
 756         return 0;
 757 }
 758
 759 static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
 760 {
 761         return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
 762 }
 763
 764 /* Caller must hold page table lock. */
 765 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 766                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
 767                 struct page *zero_page)
 768 {
 769         pmd_t entry;
 770         if (!pmd_none(*pmd))
 771                 return false;
 772         entry = mk_pmd(zero_page, vma->vm_page_prot);
 773         entry = pmd_mkhuge(entry);
 774         pgtable_trans_huge_deposit(mm, pmd, pgtable);
 775         set_pmd_at(mm, haddr, pmd, entry);
 776         atomic_long_inc(&mm->nr_ptes);
 777         return true;
 778 }
 779
 780 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 781                                unsigned long address, pmd_t *pmd,
 782                                unsigned int flags)
 783 {
 784         gfp_t gfp;
 785         struct page *page;
 786         unsigned long haddr = address & HPAGE_PMD_MASK;
 787
 788         if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
 789                 return VM_FAULT_FALLBACK;
 790         if (unlikely(anon_vma_prepare(vma)))
 791                 return VM_FAULT_OOM;
 792         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
 793                 return VM_FAULT_OOM;
 794         if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) &&
 795                         transparent_hugepage_use_zero_page()) {
 796                 spinlock_t *ptl;
 797                 pgtable_t pgtable;
 798                 struct page *zero_page;
 799                 bool set;
 800                 pgtable = pte_alloc_one(mm, haddr);
 801                 if (unlikely(!pgtable))
 802                         return VM_FAULT_OOM;
 803                 zero_page = get_huge_zero_page();
 804                 if (unlikely(!zero_page)) {
 805                         pte_free(mm, pgtable);
 806                         count_vm_event(THP_FAULT_FALLBACK);
 807                         return VM_FAULT_FALLBACK;
 808                 }
 809                 ptl = pmd_lock(mm, pmd);
 810                 set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
 811                                 zero_page);
 812                 spin_unlock(ptl);
 813                 if (!set) {
 814                         pte_free(mm, pgtable);
 815                         put_huge_zero_page();
 816                 }
 817                 return 0;
 818         }
 819         gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
 820         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
 821         if (unlikely(!page)) {
 822                 count_vm_event(THP_FAULT_FALLBACK);
 823                 return VM_FAULT_FALLBACK;
 824         }
 825         if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page))) {
 826                 put_page(page);
 827                 count_vm_event(THP_FAULT_FALLBACK);
 828                 return VM_FAULT_FALLBACK;
 829         }
 830
 831         count_vm_event(THP_FAULT_ALLOC);
 832         return 0;
 833 }
 834
 835 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 836                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
 837                   struct vm_area_struct *vma)
 838 {
 839         spinlock_t *dst_ptl, *src_ptl;
 840         struct page *src_page;
 841         pmd_t pmd;
 842         pgtable_t pgtable;
 843         int ret;
 844
 845         ret = -ENOMEM;
 846         pgtable = pte_alloc_one(dst_mm, addr);
 847         if (unlikely(!pgtable))
 848                 goto out;
 849
 850         dst_ptl = pmd_lock(dst_mm, dst_pmd);
 851         src_ptl = pmd_lockptr(src_mm, src_pmd);
 852         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
 853
 854         ret = -EAGAIN;
 855         pmd = *src_pmd;
 856         if (unlikely(!pmd_trans_huge(pmd))) {
 857                 pte_free(dst_mm, pgtable);
 858                 goto out_unlock;
 859         }
 860         /*
 861          * When page table lock is held, the huge zero pmd should not be
 862          * under splitting since we don't split the page itself, only pmd to
 863          * a page table.
 864          */
 865         if (is_huge_zero_pmd(pmd)) {
 866                 struct page *zero_page;
 867                 bool set;
 868                 /*
 869                  * get_huge_zero_page() will never allocate a new page here,
 870                  * since we already have a zero page to copy. It just takes a
 871                  * reference.
 872                  */
 873                 zero_page = get_huge_zero_page();
 874                 set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
 875                                 zero_page);
 876                 BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
 877                 ret = 0;
 878                 goto out_unlock;
 879         }
 880
 881         if (unlikely(pmd_trans_splitting(pmd))) {
 882                 /* split huge page running from under us */
 883                 spin_unlock(src_ptl);
 884                 spin_unlock(dst_ptl);
 885                 pte_free(dst_mm, pgtable);
 886
 887                 wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
 888                 goto out;
 889         }
 890         src_page = pmd_page(pmd);
 891         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
 892         get_page(src_page);
 893         page_dup_rmap(src_page);
 894         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 895
 896         pmdp_set_wrprotect(src_mm, addr, src_pmd);
 897         pmd = pmd_mkold(pmd_wrprotect(pmd));
 898         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 899         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 900         atomic_long_inc(&dst_mm->nr_ptes);
 901
 902         ret = 0;
 903 out_unlock:
 904         spin_unlock(src_ptl);
 905         spin_unlock(dst_ptl);
 906 out:
 907         return ret;
 908 }
 909
 910 void huge_pmd_set_accessed(struct mm_struct *mm,
 911                            struct vm_area_struct *vma,
 912                            unsigned long address,
 913                            pmd_t *pmd, pmd_t orig_pmd,
 914                            int dirty)
 915 {
 916         spinlock_t *ptl;
 917         pmd_t entry;
 918         unsigned long haddr;
 919
 920         ptl = pmd_lock(mm, pmd);
 921         if (unlikely(!pmd_same(*pmd, orig_pmd)))
 922                 goto unlock;
 923
 924         entry = pmd_mkyoung(orig_pmd);
 925         haddr = address & HPAGE_PMD_MASK;
 926         if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
 927                 update_mmu_cache_pmd(vma, address, pmd);
 928
 929 unlock:
 930         spin_unlock(ptl);
 931 }
 932
 933 /*
 934  * Save CONFIG_DEBUG_PAGEALLOC from faulting falsely on tail pages
 935  * during copy_user_huge_page()'s copy_page_rep(): in the case when
 936  * the source page gets split and a tail freed before copy completes.
 937  * Called under pmd_lock of checked pmd, so safe from splitting itself.
 938  */
 939 static void get_user_huge_page(struct page *page)
 940 {
 941         if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
 942                 struct page *endpage = page + HPAGE_PMD_NR;
 943
 944                 atomic_add(HPAGE_PMD_NR, &page->_count);
 945                 while (++page < endpage)
 946                         get_huge_page_tail(page);
 947         } else {
 948                 get_page(page);
 949         }
 950 }
 951
 952 static void put_user_huge_page(struct page *page)
 953 {
 954         if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
 955                 struct page *endpage = page + HPAGE_PMD_NR;
 956
 957                 while (page < endpage)
 958                         put_page(page++);
 959         } else {
 960                 put_page(page);
 961         }
 962 }
 963
 964 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
 965                                         struct vm_area_struct *vma,
 966                                         unsigned long address,
 967                                         pmd_t *pmd, pmd_t orig_pmd,
 968                                         struct page *page,
 969                                         unsigned long haddr)
 970 {
 971         struct mem_cgroup *memcg;
 972         spinlock_t *ptl;
 973         pgtable_t pgtable;
 974         pmd_t _pmd;
 975         int ret = 0, i;
 976         struct page **pages;
 977         unsigned long mmun_start;       /* For mmu_notifiers */
 978         unsigned long mmun_end;         /* For mmu_notifiers */
 979
 980         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
 981                         GFP_KERNEL);
 982         if (unlikely(!pages)) {
 983                 ret |= VM_FAULT_OOM;
 984                 goto out;
 985         }
 986
 987         for (i = 0; i < HPAGE_PMD_NR; i++) {
 988                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
 989                                                __GFP_OTHER_NODE,
 990                                                vma, address, page_to_nid(page));
 991                 if (unlikely(!pages[i] ||
 992                              mem_cgroup_try_charge(pages[i], mm, GFP_KERNEL,
 993                                                    &memcg))) {
 994                         if (pages[i])
 995                                 put_page(pages[i]);
 996                         while (--i >= 0) {
 997                                 memcg = (void *)page_private(pages[i]);
 998                                 set_page_private(pages[i], 0);
 999                                 mem_cgroup_cancel_charge(pages[i], memcg);
1000                                 put_page(pages[i]);
1001                         }
1002                         kfree(pages);
1003                         ret |= VM_FAULT_OOM;
1004                         goto out;
1005                 }
1006                 set_page_private(pages[i], (unsigned long)memcg);
1007         }
1008
1009         for (i = 0; i < HPAGE_PMD_NR; i++) {
1010                 copy_user_highpage(pages[i], page + i,
1011                                    haddr + PAGE_SIZE * i, vma);
1012                 __SetPageUptodate(pages[i]);
1013                 cond_resched();
1014         }
1015
1016         mmun_start = haddr;
1017         mmun_end   = haddr + HPAGE_PMD_SIZE;
1018         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1019
1020         ptl = pmd_lock(mm, pmd);
1021         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1022                 goto out_free_pages;
1023         VM_BUG_ON_PAGE(!PageHead(page), page);
1024
1025         pmdp_clear_flush_notify(vma, haddr, pmd);
1026         /* leave pmd empty until pte is filled */
1027
1028         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1029         pmd_populate(mm, &_pmd, pgtable);
1030
1031         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1032                 pte_t *pte, entry;
1033                 entry = mk_pte(pages[i], vma->vm_page_prot);
1034                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1035                 memcg = (void *)page_private(pages[i]);
1036                 set_page_private(pages[i], 0);
1037                 page_add_new_anon_rmap(pages[i], vma, haddr);
1038                 mem_cgroup_commit_charge(pages[i], memcg, false);
1039                 lru_cache_add_active_or_unevictable(pages[i], vma);
1040                 pte = pte_offset_map(&_pmd, haddr);
1041                 VM_BUG_ON(!pte_none(*pte));
1042                 set_pte_at(mm, haddr, pte, entry);
1043                 pte_unmap(pte);
1044         }
1045         kfree(pages);
1046
1047         smp_wmb(); /* make pte visible before pmd */
1048         pmd_populate(mm, pmd, pgtable);
1049         page_remove_rmap(page);
1050         spin_unlock(ptl);
1051
1052         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1053
1054         ret |= VM_FAULT_WRITE;
1055         put_page(page);
1056
1057 out:
1058         return ret;
1059
1060 out_free_pages:
1061         spin_unlock(ptl);
1062         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1063         for (i = 0; i < HPAGE_PMD_NR; i++) {
1064                 memcg = (void *)page_private(pages[i]);
1065                 set_page_private(pages[i], 0);
1066                 mem_cgroup_cancel_charge(pages[i], memcg);
1067                 put_page(pages[i]);
1068         }
1069         kfree(pages);
1070         goto out;
1071 }
1072
1073 int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
1074                         unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
1075 {
1076         spinlock_t *ptl;
1077         int ret = 0;
1078         struct page *page = NULL, *new_page;
1079         struct mem_cgroup *memcg;
1080         unsigned long haddr;
1081         unsigned long mmun_start;       /* For mmu_notifiers */
1082         unsigned long mmun_end;         /* For mmu_notifiers */
1083
1084         ptl = pmd_lockptr(mm, pmd);
1085         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1086         haddr = address & HPAGE_PMD_MASK;
1087         if (is_huge_zero_pmd(orig_pmd))
1088                 goto alloc;
1089         spin_lock(ptl);
1090         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1091                 goto out_unlock;
1092
1093         page = pmd_page(orig_pmd);
1094         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1095         if (page_mapcount(page) == 1) {
1096                 pmd_t entry;
1097                 entry = pmd_mkyoung(orig_pmd);
1098                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1099                 if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
1100                         update_mmu_cache_pmd(vma, address, pmd);
1101                 ret |= VM_FAULT_WRITE;
1102                 goto out_unlock;
1103         }
1104         get_user_huge_page(page);
1105         spin_unlock(ptl);
1106 alloc:
1107         if (transparent_hugepage_enabled(vma) &&
1108             !transparent_hugepage_debug_cow()) {
1109                 gfp_t gfp;
1110
1111                 gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
1112                 new_page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
1113         } else
1114                 new_page = NULL;
1115
1116         if (unlikely(!new_page)) {
1117                 if (!page) {
1118                         split_huge_page_pmd(vma, address, pmd);
1119                         ret |= VM_FAULT_FALLBACK;
1120                 } else {
1121                         ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
1122                                         pmd, orig_pmd, page, haddr);
1123                         if (ret & VM_FAULT_OOM) {
1124                                 split_huge_page(page);
1125                                 ret |= VM_FAULT_FALLBACK;
1126                         }
1127                         put_user_huge_page(page);
1128                 }
1129                 count_vm_event(THP_FAULT_FALLBACK);
1130                 goto out;
1131         }
1132
1133         if (unlikely(mem_cgroup_try_charge(new_page, mm,
1134                                            GFP_TRANSHUGE, &memcg))) {
1135                 put_page(new_page);
1136                 if (page) {
1137                         split_huge_page(page);
1138                         put_user_huge_page(page);
1139                 } else
1140                         split_huge_page_pmd(vma, address, pmd);
1141                 ret |= VM_FAULT_FALLBACK;
1142                 count_vm_event(THP_FAULT_FALLBACK);
1143                 goto out;
1144         }
1145
1146         count_vm_event(THP_FAULT_ALLOC);
1147
1148         if (!page)
1149                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1150         else
1151                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1152         __SetPageUptodate(new_page);
1153
1154         mmun_start = haddr;
1155         mmun_end   = haddr + HPAGE_PMD_SIZE;
1156         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1157
1158         spin_lock(ptl);
1159         if (page)
1160                 put_user_huge_page(page);
1161         if (unlikely(!pmd_same(*pmd, orig_pmd))) {
1162                 spin_unlock(ptl);
1163                 mem_cgroup_cancel_charge(new_page, memcg);
1164                 put_page(new_page);
1165                 goto out_mn;
1166         } else {
1167                 pmd_t entry;
1168                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1169                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1170                 pmdp_clear_flush_notify(vma, haddr, pmd);
1171                 page_add_new_anon_rmap(new_page, vma, haddr);
1172                 mem_cgroup_commit_charge(new_page, memcg, false);
1173                 lru_cache_add_active_or_unevictable(new_page, vma);
1174                 set_pmd_at(mm, haddr, pmd, entry);
1175                 update_mmu_cache_pmd(vma, address, pmd);
1176                 if (!page) {
1177                         add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
1178                         put_huge_zero_page();
1179                 } else {
1180                         VM_BUG_ON_PAGE(!PageHead(page), page);
1181                         page_remove_rmap(page);
1182                         put_page(page);
1183                 }
1184                 ret |= VM_FAULT_WRITE;
1185         }
1186         spin_unlock(ptl);
1187 out_mn:
1188         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1189 out:
1190         return ret;
1191 out_unlock:
1192         spin_unlock(ptl);
1193         return ret;
1194 }
1195
1196 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1197                                    unsigned long addr,
1198                                    pmd_t *pmd,
1199                                    unsigned int flags)
1200 {
1201         struct mm_struct *mm = vma->vm_mm;
1202         struct page *page = NULL;
1203
1204         assert_spin_locked(pmd_lockptr(mm, pmd));
1205
1206         if (flags & FOLL_WRITE && !pmd_write(*pmd))
1207                 goto out;
1208
1209         /* Avoid dumping huge zero page */
1210         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1211                 return ERR_PTR(-EFAULT);
1212
1213         /* Full NUMA hinting faults to serialise migration in fault paths */
1214         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1215                 goto out;
1216
1217         page = pmd_page(*pmd);
1218         VM_BUG_ON_PAGE(!PageHead(page), page);
1219         if (flags & FOLL_TOUCH) {
1220                 pmd_t _pmd;
1221                 /*
1222                  * We should set the dirty bit only for FOLL_WRITE but
1223                  * for now the dirty bit in the pmd is meaningless.
1224                  * And if the dirty bit will become meaningful and
1225                  * we'll only set it with FOLL_WRITE, an atomic
1226                  * set_bit will be required on the pmd to set the
1227                  * young bit, instead of the current set_pmd_at.
1228                  */
1229                 _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
1230                 if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
1231                                           pmd, _pmd,  1))
1232                         update_mmu_cache_pmd(vma, addr, pmd);
1233         }
1234         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1235                 if (page->mapping && trylock_page(page)) {
1236                         lru_add_drain();
1237                         if (page->mapping)
1238                                 mlock_vma_page(page);
1239                         unlock_page(page);
1240                 }
1241         }
1242         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1243         VM_BUG_ON_PAGE(!PageCompound(page), page);
1244         if (flags & FOLL_GET)
1245                 get_page_foll(page);
1246
1247 out:
1248         return page;
1249 }
1250
1251 /* NUMA hinting page fault entry point for trans huge pmds */
1252 int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
1253                                 unsigned long addr, pmd_t pmd, pmd_t *pmdp)
1254 {
1255         spinlock_t *ptl;
1256         struct anon_vma *anon_vma = NULL;
1257         struct page *page;
1258         unsigned long haddr = addr & HPAGE_PMD_MASK;
1259         int page_nid = -1, this_nid = numa_node_id();
1260         int target_nid, last_cpupid = -1;
1261         bool page_locked;
1262         bool migrated = false;
1263         int flags = 0;
1264
1265         /* A PROT_NONE fault should not end up here */
1266         BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
1267
1268         ptl = pmd_lock(mm, pmdp);
1269         if (unlikely(!pmd_same(pmd, *pmdp)))
1270                 goto out_unlock;
1271
1272         /*
1273          * If there are potential migrations, wait for completion and retry
1274          * without disrupting NUMA hinting information. Do not relock and
1275          * check_same as the page may no longer be mapped.
1276          */
1277         if (unlikely(pmd_trans_migrating(*pmdp))) {
1278                 page = pmd_page(*pmdp);
1279                 spin_unlock(ptl);
1280                 wait_on_page_locked(page);
1281                 goto out;
1282         }
1283
1284         page = pmd_page(pmd);
1285         BUG_ON(is_huge_zero_page(page));
1286         page_nid = page_to_nid(page);
1287         last_cpupid = page_cpupid_last(page);
1288         count_vm_numa_event(NUMA_HINT_FAULTS);
1289         if (page_nid == this_nid) {
1290                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1291                 flags |= TNF_FAULT_LOCAL;
1292         }
1293
1294         /*
1295          * Avoid grouping on DSO/COW pages in specific and RO pages
1296          * in general, RO pages shouldn't hurt as much anyway since
1297          * they can be in shared cache state.
1298          */
1299         if (!pmd_write(pmd))
1300                 flags |= TNF_NO_GROUP;
1301
1302         /*
1303          * Acquire the page lock to serialise THP migrations but avoid dropping
1304          * page_table_lock if at all possible
1305          */
1306         page_locked = trylock_page(page);
1307         target_nid = mpol_misplaced(page, vma, haddr);
1308         if (target_nid == -1) {
1309                 /* If the page was locked, there are no parallel migrations */
1310                 if (page_locked)
1311                         goto clear_pmdnuma;
1312         }
1313
1314         /* Migration could have started since the pmd_trans_migrating check */
1315         if (!page_locked) {
1316                 spin_unlock(ptl);
1317                 wait_on_page_locked(page);
1318                 page_nid = -1;
1319                 goto out;
1320         }
1321
1322         /*
1323          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1324          * to serialises splits
1325          */
1326         get_page(page);
1327         spin_unlock(ptl);
1328         anon_vma = page_lock_anon_vma_read(page);
1329
1330         /* Confirm the PMD did not change while page_table_lock was released */
1331         spin_lock(ptl);
1332         if (unlikely(!pmd_same(pmd, *pmdp))) {
1333                 unlock_page(page);
1334                 put_page(page);
1335                 page_nid = -1;
1336                 goto out_unlock;
1337         }
1338
1339         /* Bail if we fail to protect against THP splits for any reason */
1340         if (unlikely(!anon_vma)) {
1341                 put_page(page);
1342                 page_nid = -1;
1343                 goto clear_pmdnuma;
1344         }
1345
1346         /*
1347          * Migrate the THP to the requested node, returns with page unlocked
1348          * and access rights restored.
1349          */
1350         spin_unlock(ptl);
1351         migrated = migrate_misplaced_transhuge_page(mm, vma,
1352                                 pmdp, pmd, addr, page, target_nid);
1353         if (migrated) {
1354                 flags |= TNF_MIGRATED;
1355                 page_nid = target_nid;
1356         }
1357
1358         goto out;
1359 clear_pmdnuma:
1360         BUG_ON(!PageLocked(page));
1361         pmd = pmd_modify(pmd, vma->vm_page_prot);
1362         set_pmd_at(mm, haddr, pmdp, pmd);
1363         update_mmu_cache_pmd(vma, addr, pmdp);
1364         unlock_page(page);
1365 out_unlock:
1366         spin_unlock(ptl);
1367
1368 out:
1369         if (anon_vma)
1370                 page_unlock_anon_vma_read(anon_vma);
1371
1372         if (page_nid != -1)
1373                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, flags);
1374
1375         return 0;
1376 }
1377
1378 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1379                  pmd_t *pmd, unsigned long addr)
1380 {
1381         spinlock_t *ptl;
1382         int ret = 0;
1383
1384         if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1385                 struct page *page;
1386                 pgtable_t pgtable;
1387                 pmd_t orig_pmd;
1388                 /*
1389                  * For architectures like ppc64 we look at deposited pgtable
1390                  * when calling pmdp_get_and_clear. So do the
1391                  * pgtable_trans_huge_withdraw after finishing pmdp related
1392                  * operations.
1393                  */
1394                 orig_pmd = pmdp_get_and_clear_full(tlb->mm, addr, pmd,
1395                                                    tlb->fullmm);
1396                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1397                 pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1398                 if (is_huge_zero_pmd(orig_pmd)) {
1399                         atomic_long_dec(&tlb->mm->nr_ptes);
1400                         spin_unlock(ptl);
1401                         put_huge_zero_page();
1402                 } else {
1403                         page = pmd_page(orig_pmd);
1404                         page_remove_rmap(page);
1405                         VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1406                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1407                         VM_BUG_ON_PAGE(!PageHead(page), page);
1408                         atomic_long_dec(&tlb->mm->nr_ptes);
1409                         spin_unlock(ptl);
1410                         tlb_remove_page(tlb, page);
1411                 }
1412                 pte_free(tlb->mm, pgtable);
1413                 ret = 1;
1414         }
1415         return ret;
1416 }
1417
1418 int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
1419                   unsigned long old_addr,
1420                   unsigned long new_addr, unsigned long old_end,
1421                   pmd_t *old_pmd, pmd_t *new_pmd)
1422 {
1423         spinlock_t *old_ptl, *new_ptl;
1424         int ret = 0;
1425         pmd_t pmd;
1426
1427         struct mm_struct *mm = vma->vm_mm;
1428
1429         if ((old_addr & ~HPAGE_PMD_MASK) ||
1430             (new_addr & ~HPAGE_PMD_MASK) ||
1431             old_end - old_addr < HPAGE_PMD_SIZE ||
1432             (new_vma->vm_flags & VM_NOHUGEPAGE))
1433                 goto out;
1434
1435         /*
1436          * The destination pmd shouldn't be established, free_pgtables()
1437          * should have release it.
1438          */
1439         if (WARN_ON(!pmd_none(*new_pmd))) {
1440                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1441                 goto out;
1442         }
1443
1444         /*
1445          * We don't have to worry about the ordering of src and dst
1446          * ptlocks because exclusive mmap_sem prevents deadlock.
1447          */
1448         ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
1449         if (ret == 1) {
1450                 new_ptl = pmd_lockptr(mm, new_pmd);
1451                 if (new_ptl != old_ptl)
1452                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1453                 pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
1454                 VM_BUG_ON(!pmd_none(*new_pmd));
1455
1456                 if (pmd_move_must_withdraw(new_ptl, old_ptl)) {
1457                         pgtable_t pgtable;
1458                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1459                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1460                 }
1461                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1462                 if (new_ptl != old_ptl)
1463                         spin_unlock(new_ptl);
1464                 spin_unlock(old_ptl);
1465         }
1466 out:
1467         return ret;
1468 }
1469
1470 /*
1471  * Returns
1472  *  - 0 if PMD could not be locked
1473  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1474  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1475  */
1476 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1477                 unsigned long addr, pgprot_t newprot, int prot_numa)
1478 {
1479         struct mm_struct *mm = vma->vm_mm;
1480         spinlock_t *ptl;
1481         int ret = 0;
1482
1483         if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1484                 pmd_t entry;
1485
1486                 /*
1487                  * Avoid trapping faults against the zero page. The read-only
1488                  * data is likely to be read-cached on the local CPU and
1489                  * local/remote hits to the zero page are not interesting.
1490                  */
1491                 if (prot_numa && is_huge_zero_pmd(*pmd)) {
1492                         spin_unlock(ptl);
1493                         return 0;
1494                 }
1495
1496                 if (!prot_numa || !pmd_protnone(*pmd)) {
1497                         ret = 1;
1498                         entry = pmdp_get_and_clear_notify(mm, addr, pmd);
1499                         entry = pmd_modify(entry, newprot);
1500                         ret = HPAGE_PMD_NR;
1501                         set_pmd_at(mm, addr, pmd, entry);
1502                         BUG_ON(pmd_write(entry));
1503                 }
1504                 spin_unlock(ptl);
1505         }
1506
1507         return ret;
1508 }
1509
1510 /*
1511  * Returns 1 if a given pmd maps a stable (not under splitting) thp.
1512  * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
1513  *
1514  * Note that if it returns 1, this routine returns without unlocking page
1515  * table locks. So callers must unlock them.
1516  */
1517 int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
1518                 spinlock_t **ptl)
1519 {
1520         *ptl = pmd_lock(vma->vm_mm, pmd);
1521         if (likely(pmd_trans_huge(*pmd))) {
1522                 if (unlikely(pmd_trans_splitting(*pmd))) {
1523                         spin_unlock(*ptl);
1524                         wait_split_huge_page(vma->anon_vma, pmd);
1525                         return -1;
1526                 } else {
1527                         /* Thp mapped by 'pmd' is stable, so we can
1528                          * handle it as it is. */
1529                         return 1;
1530                 }
1531         }
1532         spin_unlock(*ptl);
1533         return 0;
1534 }
1535
1536 /*
1537  * This function returns whether a given @page is mapped onto the @address
1538  * in the virtual space of @mm.
1539  *
1540  * When it's true, this function returns *pmd with holding the page table lock
1541  * and passing it back to the caller via @ptl.
1542  * If it's false, returns NULL without holding the page table lock.
1543  */
1544 pmd_t *page_check_address_pmd(struct page *page,
1545                               struct mm_struct *mm,
1546                               unsigned long address,
1547                               enum page_check_address_pmd_flag flag,
1548                               spinlock_t **ptl)
1549 {
1550         pgd_t *pgd;
1551         pud_t *pud;
1552         pmd_t *pmd;
1553
1554         if (address & ~HPAGE_PMD_MASK)
1555                 return NULL;
1556
1557         pgd = pgd_offset(mm, address);
1558         if (!pgd_present(*pgd))
1559                 return NULL;
1560         pud = pud_offset(pgd, address);
1561         if (!pud_present(*pud))
1562                 return NULL;
1563         pmd = pmd_offset(pud, address);
1564
1565         *ptl = pmd_lock(mm, pmd);
1566         if (!pmd_present(*pmd))
1567                 goto unlock;
1568         if (pmd_page(*pmd) != page)
1569                 goto unlock;
1570         /*
1571          * split_vma() may create temporary aliased mappings. There is
1572          * no risk as long as all huge pmd are found and have their
1573          * splitting bit set before __split_huge_page_refcount
1574          * runs. Finding the same huge pmd more than once during the
1575          * same rmap walk is not a problem.
1576          */
1577         if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
1578             pmd_trans_splitting(*pmd))
1579                 goto unlock;
1580         if (pmd_trans_huge(*pmd)) {
1581                 VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
1582                           !pmd_trans_splitting(*pmd));
1583                 return pmd;
1584         }
1585 unlock:
1586         spin_unlock(*ptl);
1587         return NULL;
1588 }
1589
1590 static int __split_huge_page_splitting(struct page *page,
1591                                        struct vm_area_struct *vma,
1592                                        unsigned long address)
1593 {
1594         struct mm_struct *mm = vma->vm_mm;
1595         spinlock_t *ptl;
1596         pmd_t *pmd;
1597         int ret = 0;
1598         /* For mmu_notifiers */
1599         const unsigned long mmun_start = address;
1600         const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
1601
1602         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1603         pmd = page_check_address_pmd(page, mm, address,
1604                         PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG, &ptl);
1605         if (pmd) {
1606                 /*
1607                  * We can't temporarily set the pmd to null in order
1608                  * to split it, the pmd must remain marked huge at all
1609                  * times or the VM won't take the pmd_trans_huge paths
1610                  * and it won't wait on the anon_vma->root->rwsem to
1611                  * serialize against split_huge_page*.
1612                  */
1613                 pmdp_splitting_flush(vma, address, pmd);
1614
1615                 ret = 1;
1616                 spin_unlock(ptl);
1617         }
1618         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1619
1620         return ret;
1621 }
1622
1623 static void __split_huge_page_refcount(struct page *page,
1624                                        struct list_head *list)
1625 {
1626         int i;
1627         struct zone *zone = page_zone(page);
1628         struct lruvec *lruvec;
1629         int tail_count = 0;
1630
1631         /* prevent PageLRU to go away from under us, and freeze lru stats */
1632         spin_lock_irq(&zone->lru_lock);
1633         lruvec = mem_cgroup_page_lruvec(page, zone);
1634
1635         compound_lock(page);
1636         /* complete memcg works before add pages to LRU */
1637         mem_cgroup_split_huge_fixup(page);
1638
1639         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1640                 struct page *page_tail = page + i;
1641
1642                 /* tail_page->_mapcount cannot change */
1643                 BUG_ON(page_mapcount(page_tail) < 0);
1644                 tail_count += page_mapcount(page_tail);
1645                 /* check for overflow */
1646                 BUG_ON(tail_count < 0);
1647                 BUG_ON(atomic_read(&page_tail->_count) != 0);
1648                 /*
1649                  * tail_page->_count is zero and not changing from
1650                  * under us. But get_page_unless_zero() may be running
1651                  * from under us on the tail_page. If we used
1652                  * atomic_set() below instead of atomic_add(), we
1653                  * would then run atomic_set() concurrently with
1654                  * get_page_unless_zero(), and atomic_set() is
1655                  * implemented in C not using locked ops. spin_unlock
1656                  * on x86 sometime uses locked ops because of PPro
1657                  * errata 66, 92, so unless somebody can guarantee
1658                  * atomic_set() here would be safe on all archs (and
1659                  * not only on x86), it's safer to use atomic_add().
1660                  */
1661                 atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
1662                            &page_tail->_count);
1663
1664                 /* after clearing PageTail the gup refcount can be released */
1665                 smp_mb__after_atomic();
1666
1667                 /*
1668                  * retain hwpoison flag of the poisoned tail page:
1669                  *   fix for the unsuitable process killed on Guest Machine(KVM)
1670                  *   by the memory-failure.
1671                  */
1672                 page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;
1673                 page_tail->flags |= (page->flags &
1674                                      ((1L << PG_referenced) |
1675                                       (1L << PG_swapbacked) |
1676                                       (1L << PG_mlocked) |
1677                                       (1L << PG_uptodate) |
1678                                       (1L << PG_active) |
1679                                       (1L << PG_unevictable)));
1680                 page_tail->flags |= (1L << PG_dirty);
1681
1682                 /* clear PageTail before overwriting first_page */
1683                 smp_wmb();
1684
1685                 /*
1686                  * __split_huge_page_splitting() already set the
1687                  * splitting bit in all pmd that could map this
1688                  * hugepage, that will ensure no CPU can alter the
1689                  * mapcount on the head page. The mapcount is only
1690                  * accounted in the head page and it has to be
1691                  * transferred to all tail pages in the below code. So
1692                  * for this code to be safe, the split the mapcount
1693                  * can't change. But that doesn't mean userland can't
1694                  * keep changing and reading the page contents while
1695                  * we transfer the mapcount, so the pmd splitting
1696                  * status is achieved setting a reserved bit in the
1697                  * pmd, not by clearing the present bit.
1698                 */
1699                 page_tail->_mapcount = page->_mapcount;
1700
1701                 BUG_ON(page_tail->mapping);
1702                 page_tail->mapping = page->mapping;
1703
1704                 page_tail->index = page->index + i;
1705                 page_cpupid_xchg_last(page_tail, page_cpupid_last(page));
1706
1707                 BUG_ON(!PageAnon(page_tail));
1708                 BUG_ON(!PageUptodate(page_tail));
1709                 BUG_ON(!PageDirty(page_tail));
1710                 BUG_ON(!PageSwapBacked(page_tail));
1711
1712                 lru_add_page_tail(page, page_tail, lruvec, list);
1713         }
1714         atomic_sub(tail_count, &page->_count);
1715         BUG_ON(atomic_read(&page->_count) <= 0);
1716
1717         __mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
1718
1719         ClearPageCompound(page);
1720         compound_unlock(page);
1721         spin_unlock_irq(&zone->lru_lock);
1722
1723         for (i = 1; i < HPAGE_PMD_NR; i++) {
1724                 struct page *page_tail = page + i;
1725                 BUG_ON(page_count(page_tail) <= 0);
1726                 /*
1727                  * Tail pages may be freed if there wasn't any mapping
1728                  * like if add_to_swap() is running on a lru page that
1729                  * had its mapping zapped. And freeing these pages
1730                  * requires taking the lru_lock so we do the put_page
1731                  * of the tail pages after the split is complete.
1732                  */
1733                 put_page(page_tail);
1734         }
1735
1736         /*
1737          * Only the head page (now become a regular page) is required
1738          * to be pinned by the caller.
1739          */
1740         BUG_ON(page_count(page) <= 0);
1741 }
1742
1743 static int __split_huge_page_map(struct page *page,
1744                                  struct vm_area_struct *vma,
1745                                  unsigned long address)
1746 {
1747         struct mm_struct *mm = vma->vm_mm;
1748         spinlock_t *ptl;
1749         pmd_t *pmd, _pmd;
1750         int ret = 0, i;
1751         pgtable_t pgtable;
1752         unsigned long haddr;
1753
1754         pmd = page_check_address_pmd(page, mm, address,
1755                         PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG, &ptl);
1756         if (pmd) {
1757                 pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1758                 pmd_populate(mm, &_pmd, pgtable);
1759                 if (pmd_write(*pmd))
1760                         BUG_ON(page_mapcount(page) != 1);
1761
1762                 haddr = address;
1763                 for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1764                         pte_t *pte, entry;
1765                         BUG_ON(PageCompound(page+i));
1766                         /*
1767                          * Note that NUMA hinting access restrictions are not
1768                          * transferred to avoid any possibility of altering
1769                          * permissions across VMAs.
1770                          */
1771                         entry = mk_pte(page + i, vma->vm_page_prot);
1772                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1773                         if (!pmd_write(*pmd))
1774                                 entry = pte_wrprotect(entry);
1775                         if (!pmd_young(*pmd))
1776                                 entry = pte_mkold(entry);
1777                         pte = pte_offset_map(&_pmd, haddr);
1778                         BUG_ON(!pte_none(*pte));
1779                         set_pte_at(mm, haddr, pte, entry);
1780                         pte_unmap(pte);
1781                 }
1782
1783                 smp_wmb(); /* make pte visible before pmd */
1784                 /*
1785                  * Up to this point the pmd is present and huge and
1786                  * userland has the whole access to the hugepage
1787                  * during the split (which happens in place). If we
1788                  * overwrite the pmd with the not-huge version
1789                  * pointing to the pte here (which of course we could
1790                  * if all CPUs were bug free), userland could trigger
1791                  * a small page size TLB miss on the small sized TLB
1792                  * while the hugepage TLB entry is still established
1793                  * in the huge TLB. Some CPU doesn't like that. See
1794                  * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
1795                  * Erratum 383 on page 93. Intel should be safe but is
1796                  * also warns that it's only safe if the permission
1797                  * and cache attributes of the two entries loaded in
1798                  * the two TLB is identical (which should be the case
1799                  * here). But it is generally safer to never allow
1800                  * small and huge TLB entries for the same virtual
1801                  * address to be loaded simultaneously. So instead of
1802                  * doing "pmd_populate(); flush_tlb_range();" we first
1803                  * mark the current pmd notpresent (atomically because
1804                  * here the pmd_trans_huge and pmd_trans_splitting
1805                  * must remain set at all times on the pmd until the
1806                  * split is complete for this pmd), then we flush the
1807                  * SMP TLB and finally we write the non-huge version
1808                  * of the pmd entry with pmd_populate.
1809                  */
1810                 pmdp_invalidate(vma, address, pmd);
1811                 pmd_populate(mm, pmd, pgtable);
1812                 ret = 1;
1813                 spin_unlock(ptl);
1814         }
1815
1816         return ret;
1817 }
1818
1819 /* must be called with anon_vma->root->rwsem held */
1820 static void __split_huge_page(struct page *page,
1821                               struct anon_vma *anon_vma,
1822                               struct list_head *list)
1823 {
1824         int mapcount, mapcount2;
1825         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1826         struct anon_vma_chain *avc;
1827
1828         BUG_ON(!PageHead(page));
1829         BUG_ON(PageTail(page));
1830
1831         mapcount = 0;
1832         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1833                 struct vm_area_struct *vma = avc->vma;
1834                 unsigned long addr = vma_address(page, vma);
1835                 BUG_ON(is_vma_temporary_stack(vma));
1836                 mapcount += __split_huge_page_splitting(page, vma, addr);
1837         }
1838         /*
1839          * It is critical that new vmas are added to the tail of the
1840          * anon_vma list. This guarantes that if copy_huge_pmd() runs
1841          * and establishes a child pmd before
1842          * __split_huge_page_splitting() freezes the parent pmd (so if
1843          * we fail to prevent copy_huge_pmd() from running until the
1844          * whole __split_huge_page() is complete), we will still see
1845          * the newly established pmd of the child later during the
1846          * walk, to be able to set it as pmd_trans_splitting too.
1847          */
1848         if (mapcount != page_mapcount(page)) {
1849                 pr_err("mapcount %d page_mapcount %d\n",
1850                         mapcount, page_mapcount(page));
1851                 BUG();
1852         }
1853
1854         __split_huge_page_refcount(page, list);
1855
1856         mapcount2 = 0;
1857         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1858                 struct vm_area_struct *vma = avc->vma;
1859                 unsigned long addr = vma_address(page, vma);
1860                 BUG_ON(is_vma_temporary_stack(vma));
1861                 mapcount2 += __split_huge_page_map(page, vma, addr);
1862         }
1863         if (mapcount != mapcount2) {
1864                 pr_err("mapcount %d mapcount2 %d page_mapcount %d\n",
1865                         mapcount, mapcount2, page_mapcount(page));
1866                 BUG();
1867         }
1868 }
1869
1870 /*
1871  * Split a hugepage into normal pages. This doesn't change the position of head
1872  * page. If @list is null, tail pages will be added to LRU list, otherwise, to
1873  * @list. Both head page and tail pages will inherit mapping, flags, and so on
1874  * from the hugepage.
1875  * Return 0 if the hugepage is split successfully otherwise return 1.
1876  */
1877 int split_huge_page_to_list(struct page *page, struct list_head *list)
1878 {
1879         struct anon_vma *anon_vma;
1880         int ret = 1;
1881
1882         BUG_ON(is_huge_zero_page(page));
1883         BUG_ON(!PageAnon(page));
1884
1885         /*
1886          * The caller does not necessarily hold an mmap_sem that would prevent
1887          * the anon_vma disappearing so we first we take a reference to it
1888          * and then lock the anon_vma for write. This is similar to
1889          * page_lock_anon_vma_read except the write lock is taken to serialise
1890          * against parallel split or collapse operations.
1891          */
1892         anon_vma = page_get_anon_vma(page);
1893         if (!anon_vma)
1894                 goto out;
1895         anon_vma_lock_write(anon_vma);
1896
1897         ret = 0;
1898         if (!PageCompound(page))
1899                 goto out_unlock;
1900
1901         BUG_ON(!PageSwapBacked(page));
1902         __split_huge_page(page, anon_vma, list);
1903         count_vm_event(THP_SPLIT);
1904
1905         BUG_ON(PageCompound(page));
1906 out_unlock:
1907         anon_vma_unlock_write(anon_vma);
1908         put_anon_vma(anon_vma);
1909 out:
1910         return ret;
1911 }
1912
1913 #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
1914
1915 int hugepage_madvise(struct vm_area_struct *vma,
1916                      unsigned long *vm_flags, int advice)
1917 {
1918         switch (advice) {
1919         case MADV_HUGEPAGE:
1920 #ifdef CONFIG_S390
1921                 /*
1922                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
1923                  * can't handle this properly after s390_enable_sie, so we simply
1924                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
1925                  */
1926                 if (mm_has_pgste(vma->vm_mm))
1927                         return 0;
1928 #endif
1929                 /*
1930                  * Be somewhat over-protective like KSM for now!
1931                  */
1932                 if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
1933                         return -EINVAL;
1934                 *vm_flags &= ~VM_NOHUGEPAGE;
1935                 *vm_flags |= VM_HUGEPAGE;
1936                 /*
1937                  * If the vma become good for khugepaged to scan,
1938                  * register it here without waiting a page fault that
1939                  * may not happen any time soon.
1940                  */
1941                 if (unlikely(khugepaged_enter_vma_merge(vma, *vm_flags)))
1942                         return -ENOMEM;
1943                 break;
1944         case MADV_NOHUGEPAGE:
1945                 /*
1946                  * Be somewhat over-protective like KSM for now!
1947                  */
1948                 if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
1949                         return -EINVAL;
1950                 *vm_flags &= ~VM_HUGEPAGE;
1951                 *vm_flags |= VM_NOHUGEPAGE;
1952                 /*
1953                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
1954                  * this vma even if we leave the mm registered in khugepaged if
1955                  * it got registered before VM_NOHUGEPAGE was set.
1956                  */
1957                 break;
1958         }
1959
1960         return 0;
1961 }
1962
1963 static int __init khugepaged_slab_init(void)
1964 {
1965         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
1966                                           sizeof(struct mm_slot),
1967                                           __alignof__(struct mm_slot), 0, NULL);
1968         if (!mm_slot_cache)
1969                 return -ENOMEM;
1970
1971         return 0;
1972 }
1973
1974 static inline struct mm_slot *alloc_mm_slot(void)
1975 {
1976         if (!mm_slot_cache)     /* initialization failed */
1977                 return NULL;
1978         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
1979 }
1980
1981 static inline void free_mm_slot(struct mm_slot *mm_slot)
1982 {
1983         kmem_cache_free(mm_slot_cache, mm_slot);
1984 }
1985
1986 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
1987 {
1988         struct mm_slot *mm_slot;
1989
1990         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
1991                 if (mm == mm_slot->mm)
1992                         return mm_slot;
1993
1994         return NULL;
1995 }
1996
1997 static void insert_to_mm_slots_hash(struct mm_struct *mm,
1998                                     struct mm_slot *mm_slot)
1999 {
2000         mm_slot->mm = mm;
2001         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
2002 }
2003
2004 static inline int khugepaged_test_exit(struct mm_struct *mm)
2005 {
2006         return atomic_read(&mm->mm_users) == 0;
2007 }
2008
2009 int __khugepaged_enter(struct mm_struct *mm)
2010 {
2011         struct mm_slot *mm_slot;
2012         int wakeup;
2013
2014         mm_slot = alloc_mm_slot();
2015         if (!mm_slot)
2016                 return -ENOMEM;
2017
2018         /* __khugepaged_exit() must not run from under us */
2019         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
2020         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
2021                 free_mm_slot(mm_slot);
2022                 return 0;
2023         }
2024
2025         spin_lock(&khugepaged_mm_lock);
2026         insert_to_mm_slots_hash(mm, mm_slot);
2027         /*
2028          * Insert just behind the scanning cursor, to let the area settle
2029          * down a little.
2030          */
2031         wakeup = list_empty(&khugepaged_scan.mm_head);
2032         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
2033         spin_unlock(&khugepaged_mm_lock);
2034
2035         atomic_inc(&mm->mm_count);
2036         if (wakeup)
2037                 wake_up_interruptible(&khugepaged_wait);
2038
2039         return 0;
2040 }
2041
2042 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
2043                                unsigned long vm_flags)
2044 {
2045         unsigned long hstart, hend;
2046         if (!vma->anon_vma)
2047                 /*
2048                  * Not yet faulted in so we will register later in the
2049                  * page fault if needed.
2050                  */
2051                 return 0;
2052         if (vma->vm_ops)
2053                 /* khugepaged not yet working on file or special mappings */
2054                 return 0;
2055         VM_BUG_ON_VMA(vm_flags & VM_NO_THP, vma);
2056         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2057         hend = vma->vm_end & HPAGE_PMD_MASK;
2058         if (hstart < hend)
2059                 return khugepaged_enter(vma, vm_flags);
2060         return 0;
2061 }
2062
2063 void __khugepaged_exit(struct mm_struct *mm)
2064 {
2065         struct mm_slot *mm_slot;
2066         int free = 0;
2067
2068         spin_lock(&khugepaged_mm_lock);
2069         mm_slot = get_mm_slot(mm);
2070         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
2071                 hash_del(&mm_slot->hash);
2072                 list_del(&mm_slot->mm_node);
2073                 free = 1;
2074         }
2075         spin_unlock(&khugepaged_mm_lock);
2076
2077         if (free) {
2078                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2079                 free_mm_slot(mm_slot);
2080                 mmdrop(mm);
2081         } else if (mm_slot) {
2082                 /*
2083                  * This is required to serialize against
2084                  * khugepaged_test_exit() (which is guaranteed to run
2085                  * under mmap sem read mode). Stop here (after we
2086                  * return all pagetables will be destroyed) until
2087                  * khugepaged has finished working on the pagetables
2088                  * under the mmap_sem.
2089                  */
2090                 down_write(&mm->mmap_sem);
2091                 up_write(&mm->mmap_sem);
2092         }
2093 }
2094
2095 static void release_pte_page(struct page *page)
2096 {
2097         /* 0 stands for page_is_file_cache(page) == false */
2098         dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
2099         unlock_page(page);
2100         putback_lru_page(page);
2101 }
2102
2103 static void release_pte_pages(pte_t *pte, pte_t *_pte)
2104 {
2105         while (--_pte >= pte) {
2106                 pte_t pteval = *_pte;
2107                 if (!pte_none(pteval))
2108                         release_pte_page(pte_page(pteval));
2109         }
2110 }
2111
2112 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
2113                                         unsigned long address,
2114                                         pte_t *pte)
2115 {
2116         struct page *page;
2117         pte_t *_pte;
2118         int none = 0;
2119         bool referenced = false, writable = false;
2120         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
2121              _pte++, address += PAGE_SIZE) {
2122                 pte_t pteval = *_pte;
2123                 if (pte_none(pteval)) {
2124                         if (++none <= khugepaged_max_ptes_none)
2125                                 continue;
2126                         else
2127                                 goto out;
2128                 }
2129                 if (!pte_present(pteval))
2130                         goto out;
2131                 page = vm_normal_page(vma, address, pteval);
2132                 if (unlikely(!page))
2133                         goto out;
2134
2135                 VM_BUG_ON_PAGE(PageCompound(page), page);
2136                 VM_BUG_ON_PAGE(!PageAnon(page), page);
2137                 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2138
2139                 /*
2140                  * We can do it before isolate_lru_page because the
2141                  * page can't be freed from under us. NOTE: PG_lock
2142                  * is needed to serialize against split_huge_page
2143                  * when invoked from the VM.
2144                  */
2145                 if (!trylock_page(page))
2146                         goto out;
2147
2148                 /*
2149                  * cannot use mapcount: can't collapse if there's a gup pin.
2150                  * The page must only be referenced by the scanned process
2151                  * and page swap cache.
2152                  */
2153                 if (page_count(page) != 1 + !!PageSwapCache(page)) {
2154                         unlock_page(page);
2155                         goto out;
2156                 }
2157                 if (pte_write(pteval)) {
2158                         writable = true;
2159                 } else {
2160                         if (PageSwapCache(page) && !reuse_swap_page(page)) {
2161                                 unlock_page(page);
2162                                 goto out;
2163                         }
2164                         /*
2165                          * Page is not in the swap cache. It can be collapsed
2166                          * into a THP.
2167                          */
2168                 }
2169
2170                 /*
2171                  * Isolate the page to avoid collapsing an hugepage
2172                  * currently in use by the VM.
2173                  */
2174                 if (isolate_lru_page(page)) {
2175                         unlock_page(page);
2176                         goto out;
2177                 }
2178                 /* 0 stands for page_is_file_cache(page) == false */
2179                 inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
2180                 VM_BUG_ON_PAGE(!PageLocked(page), page);
2181                 VM_BUG_ON_PAGE(PageLRU(page), page);
2182
2183                 /* If there is no mapped pte young don't collapse the page */
2184                 if (pte_young(pteval) || PageReferenced(page) ||
2185                     mmu_notifier_test_young(vma->vm_mm, address))
2186                         referenced = true;
2187         }
2188         if (likely(referenced && writable))
2189                 return 1;
2190 out:
2191         release_pte_pages(pte, _pte);
2192         return 0;
2193 }
2194
2195 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
2196                                       struct vm_area_struct *vma,
2197                                       unsigned long address,
2198                                       spinlock_t *ptl)
2199 {
2200         pte_t *_pte;
2201         for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
2202                 pte_t pteval = *_pte;
2203                 struct page *src_page;
2204
2205                 if (pte_none(pteval)) {
2206                         clear_user_highpage(page, address);
2207                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
2208                 } else {
2209                         src_page = pte_page(pteval);
2210                         copy_user_highpage(page, src_page, address, vma);
2211                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
2212                         release_pte_page(src_page);
2213                         /*
2214                          * ptl mostly unnecessary, but preempt has to
2215                          * be disabled to update the per-cpu stats
2216                          * inside page_remove_rmap().
2217                          */
2218                         spin_lock(ptl);
2219                         /*
2220                          * paravirt calls inside pte_clear here are
2221                          * superfluous.
2222                          */
2223                         pte_clear(vma->vm_mm, address, _pte);
2224                         page_remove_rmap(src_page);
2225                         spin_unlock(ptl);
2226                         free_page_and_swap_cache(src_page);
2227                 }
2228
2229                 address += PAGE_SIZE;
2230                 page++;
2231         }
2232 }
2233
2234 static void khugepaged_alloc_sleep(void)
2235 {
2236         wait_event_freezable_timeout(khugepaged_wait, false,
2237                         msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
2238 }
2239
2240 static int khugepaged_node_load[MAX_NUMNODES];
2241
2242 static bool khugepaged_scan_abort(int nid)
2243 {
2244         int i;
2245
2246         /*
2247          * If zone_reclaim_mode is disabled, then no extra effort is made to
2248          * allocate memory locally.
2249          */
2250         if (!zone_reclaim_mode)
2251                 return false;
2252
2253         /* If there is a count for this node already, it must be acceptable */
2254         if (khugepaged_node_load[nid])
2255                 return false;
2256
2257         for (i = 0; i < MAX_NUMNODES; i++) {
2258                 if (!khugepaged_node_load[i])
2259                         continue;
2260                 if (node_distance(nid, i) > RECLAIM_DISTANCE)
2261                         return true;
2262         }
2263         return false;
2264 }
2265
2266 #ifdef CONFIG_NUMA
2267 static int khugepaged_find_target_node(void)
2268 {
2269         static int last_khugepaged_target_node = NUMA_NO_NODE;
2270         int nid, target_node = 0, max_value = 0;
2271
2272         /* find first node with max normal pages hit */
2273         for (nid = 0; nid < MAX_NUMNODES; nid++)
2274                 if (khugepaged_node_load[nid] > max_value) {
2275                         max_value = khugepaged_node_load[nid];
2276                         target_node = nid;
2277                 }
2278
2279         /* do some balance if several nodes have the same hit record */
2280         if (target_node <= last_khugepaged_target_node)
2281                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
2282                                 nid++)
2283                         if (max_value == khugepaged_node_load[nid]) {
2284                                 target_node = nid;
2285                                 break;
2286                         }
2287
2288         last_khugepaged_target_node = target_node;
2289         return target_node;
2290 }
2291
2292 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2293 {
2294         if (IS_ERR(*hpage)) {
2295                 if (!*wait)
2296                         return false;
2297
2298                 *wait = false;
2299                 *hpage = NULL;
2300                 khugepaged_alloc_sleep();
2301         } else if (*hpage) {
2302                 put_page(*hpage);
2303                 *hpage = NULL;
2304         }
2305
2306         return true;
2307 }
2308
2309 static struct page
2310 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2311                        struct vm_area_struct *vma, unsigned long address,
2312                        int node)
2313 {
2314         VM_BUG_ON_PAGE(*hpage, *hpage);
2315
2316         /*
2317          * Before allocating the hugepage, release the mmap_sem read lock.
2318          * The allocation can take potentially a long time if it involves
2319          * sync compaction, and we do not need to hold the mmap_sem during
2320          * that. We will recheck the vma after taking it again in write mode.
2321          */
2322         up_read(&mm->mmap_sem);
2323
2324         *hpage = alloc_pages_exact_node(node, alloc_hugepage_gfpmask(
2325                 khugepaged_defrag(), __GFP_OTHER_NODE), HPAGE_PMD_ORDER);
2326         if (unlikely(!*hpage)) {
2327                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2328                 *hpage = ERR_PTR(-ENOMEM);
2329                 return NULL;
2330         }
2331
2332         count_vm_event(THP_COLLAPSE_ALLOC);
2333         return *hpage;
2334 }
2335 #else
2336 static int khugepaged_find_target_node(void)
2337 {
2338         return 0;
2339 }
2340
2341 static inline struct page *alloc_hugepage(int defrag)
2342 {
2343         return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
2344                            HPAGE_PMD_ORDER);
2345 }
2346
2347 static struct page *khugepaged_alloc_hugepage(bool *wait)
2348 {
2349         struct page *hpage;
2350
2351         do {
2352                 hpage = alloc_hugepage(khugepaged_defrag());
2353                 if (!hpage) {
2354                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2355                         if (!*wait)
2356                                 return NULL;
2357
2358                         *wait = false;
2359                         khugepaged_alloc_sleep();
2360                 } else
2361                         count_vm_event(THP_COLLAPSE_ALLOC);
2362         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
2363
2364         return hpage;
2365 }
2366
2367 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2368 {
2369         if (!*hpage)
2370                 *hpage = khugepaged_alloc_hugepage(wait);
2371
2372         if (unlikely(!*hpage))
2373                 return false;
2374
2375         return true;
2376 }
2377
2378 static struct page
2379 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2380                        struct vm_area_struct *vma, unsigned long address,
2381                        int node)
2382 {
2383         up_read(&mm->mmap_sem);
2384         VM_BUG_ON(!*hpage);
2385         return  *hpage;
2386 }
2387 #endif
2388
2389 static bool hugepage_vma_check(struct vm_area_struct *vma)
2390 {
2391         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
2392             (vma->vm_flags & VM_NOHUGEPAGE))
2393                 return false;
2394
2395         if (!vma->anon_vma || vma->vm_ops)
2396                 return false;
2397         if (is_vma_temporary_stack(vma))
2398                 return false;
2399         VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma);
2400         return true;
2401 }
2402
2403 static void collapse_huge_page(struct mm_struct *mm,
2404                                    unsigned long address,
2405                                    struct page **hpage,
2406                                    struct vm_area_struct *vma,
2407                                    int node)
2408 {
2409         pmd_t *pmd, _pmd;
2410         pte_t *pte;
2411         pgtable_t pgtable;
2412         struct page *new_page;
2413         spinlock_t *pmd_ptl, *pte_ptl;
2414         int isolated;
2415         unsigned long hstart, hend;
2416         struct mem_cgroup *memcg;
2417         unsigned long mmun_start;       /* For mmu_notifiers */
2418         unsigned long mmun_end;         /* For mmu_notifiers */
2419
2420         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2421
2422         /* release the mmap_sem read lock. */
2423         new_page = khugepaged_alloc_page(hpage, mm, vma, address, node);
2424         if (!new_page)
2425                 return;
2426
2427         if (unlikely(mem_cgroup_try_charge(new_page, mm,
2428                                            GFP_TRANSHUGE, &memcg)))
2429                 return;
2430
2431         /*
2432          * Prevent all access to pagetables with the exception of
2433          * gup_fast later hanlded by the ptep_clear_flush and the VM
2434          * handled by the anon_vma lock + PG_lock.
2435          */
2436         down_write(&mm->mmap_sem);
2437         if (unlikely(khugepaged_test_exit(mm)))
2438                 goto out;
2439
2440         vma = find_vma(mm, address);
2441         if (!vma)
2442                 goto out;
2443         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2444         hend = vma->vm_end & HPAGE_PMD_MASK;
2445         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
2446                 goto out;
2447         if (!hugepage_vma_check(vma))
2448                 goto out;
2449         pmd = mm_find_pmd(mm, address);
2450         if (!pmd)
2451                 goto out;
2452
2453         anon_vma_lock_write(vma->anon_vma);
2454
2455         pte = pte_offset_map(pmd, address);
2456         pte_ptl = pte_lockptr(mm, pmd);
2457
2458         mmun_start = address;
2459         mmun_end   = address + HPAGE_PMD_SIZE;
2460         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2461         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
2462         /*
2463          * After this gup_fast can't run anymore. This also removes
2464          * any huge TLB entry from the CPU so we won't allow
2465          * huge and small TLB entries for the same virtual address
2466          * to avoid the risk of CPU bugs in that area.
2467          */
2468         _pmd = pmdp_clear_flush(vma, address, pmd);
2469         spin_unlock(pmd_ptl);
2470         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2471
2472         spin_lock(pte_ptl);
2473         isolated = __collapse_huge_page_isolate(vma, address, pte);
2474         spin_unlock(pte_ptl);
2475
2476         if (unlikely(!isolated)) {
2477                 pte_unmap(pte);
2478                 spin_lock(pmd_ptl);
2479                 BUG_ON(!pmd_none(*pmd));
2480                 /*
2481                  * We can only use set_pmd_at when establishing
2482                  * hugepmds and never for establishing regular pmds that
2483                  * points to regular pagetables. Use pmd_populate for that
2484                  */
2485                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
2486                 spin_unlock(pmd_ptl);
2487                 anon_vma_unlock_write(vma->anon_vma);
2488                 goto out;
2489         }
2490
2491         /*
2492          * All pages are isolated and locked so anon_vma rmap
2493          * can't run anymore.
2494          */
2495         anon_vma_unlock_write(vma->anon_vma);
2496
2497         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
2498         pte_unmap(pte);
2499         __SetPageUptodate(new_page);
2500         pgtable = pmd_pgtable(_pmd);
2501
2502         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
2503         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
2504
2505         /*
2506          * spin_lock() below is not the equivalent of smp_wmb(), so
2507          * this is needed to avoid the copy_huge_page writes to become
2508          * visible after the set_pmd_at() write.
2509          */
2510         smp_wmb();
2511
2512         spin_lock(pmd_ptl);
2513         BUG_ON(!pmd_none(*pmd));
2514         page_add_new_anon_rmap(new_page, vma, address);
2515         mem_cgroup_commit_charge(new_page, memcg, false);
2516         lru_cache_add_active_or_unevictable(new_page, vma);
2517         pgtable_trans_huge_deposit(mm, pmd, pgtable);
2518         set_pmd_at(mm, address, pmd, _pmd);
2519         update_mmu_cache_pmd(vma, address, pmd);
2520         spin_unlock(pmd_ptl);
2521
2522         *hpage = NULL;
2523
2524         khugepaged_pages_collapsed++;
2525 out_up_write:
2526         up_write(&mm->mmap_sem);
2527         return;
2528
2529 out:
2530         mem_cgroup_cancel_charge(new_page, memcg);
2531         goto out_up_write;
2532 }
2533
2534 static int khugepaged_scan_pmd(struct mm_struct *mm,
2535                                struct vm_area_struct *vma,
2536                                unsigned long address,
2537                                struct page **hpage)
2538 {
2539         pmd_t *pmd;
2540         pte_t *pte, *_pte;
2541         int ret = 0, none = 0;
2542         struct page *page;
2543         unsigned long _address;
2544         spinlock_t *ptl;
2545         int node = NUMA_NO_NODE;
2546         bool writable = false, referenced = false;
2547
2548         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2549
2550         pmd = mm_find_pmd(mm, address);
2551         if (!pmd)
2552                 goto out;
2553
2554         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
2555         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
2556         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
2557              _pte++, _address += PAGE_SIZE) {
2558                 pte_t pteval = *_pte;
2559                 if (pte_none(pteval)) {
2560                         if (++none <= khugepaged_max_ptes_none)
2561                                 continue;
2562                         else
2563                                 goto out_unmap;
2564                 }
2565                 if (!pte_present(pteval))
2566                         goto out_unmap;
2567                 if (pte_write(pteval))
2568                         writable = true;
2569
2570                 page = vm_normal_page(vma, _address, pteval);
2571                 if (unlikely(!page))
2572                         goto out_unmap;
2573                 /*
2574                  * Record which node the original page is from and save this
2575                  * information to khugepaged_node_load[].
2576                  * Khupaged will allocate hugepage from the node has the max
2577                  * hit record.
2578                  */
2579                 node = page_to_nid(page);
2580                 if (khugepaged_scan_abort(node))
2581                         goto out_unmap;
2582                 khugepaged_node_load[node]++;
2583                 VM_BUG_ON_PAGE(PageCompound(page), page);
2584                 if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
2585                         goto out_unmap;
2586                 /*
2587                  * cannot use mapcount: can't collapse if there's a gup pin.
2588                  * The page must only be referenced by the scanned process
2589                  * and page swap cache.
2590                  */
2591                 if (page_count(page) != 1 + !!PageSwapCache(page))
2592                         goto out_unmap;
2593                 if (pte_young(pteval) || PageReferenced(page) ||
2594                     mmu_notifier_test_young(vma->vm_mm, address))
2595                         referenced = true;
2596         }
2597         if (referenced && writable)
2598                 ret = 1;
2599 out_unmap:
2600         pte_unmap_unlock(pte, ptl);
2601         if (ret) {
2602                 node = khugepaged_find_target_node();
2603                 /* collapse_huge_page will return with the mmap_sem released */
2604                 collapse_huge_page(mm, address, hpage, vma, node);
2605         }
2606 out:
2607         return ret;
2608 }
2609
2610 static void collect_mm_slot(struct mm_slot *mm_slot)
2611 {
2612         struct mm_struct *mm = mm_slot->mm;
2613
2614         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2615
2616         if (khugepaged_test_exit(mm)) {
2617                 /* free mm_slot */
2618                 hash_del(&mm_slot->hash);
2619                 list_del(&mm_slot->mm_node);
2620
2621                 /*
2622                  * Not strictly needed because the mm exited already.
2623                  *
2624                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2625                  */
2626
2627                 /* khugepaged_mm_lock actually not necessary for the below */
2628                 free_mm_slot(mm_slot);
2629                 mmdrop(mm);
2630         }
2631 }
2632
2633 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2634                                             struct page **hpage)
2635         __releases(&khugepaged_mm_lock)
2636         __acquires(&khugepaged_mm_lock)
2637 {
2638         struct mm_slot *mm_slot;
2639         struct mm_struct *mm;
2640         struct vm_area_struct *vma;
2641         int progress = 0;
2642
2643         VM_BUG_ON(!pages);
2644         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2645
2646         if (khugepaged_scan.mm_slot)
2647                 mm_slot = khugepaged_scan.mm_slot;
2648         else {
2649                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
2650                                      struct mm_slot, mm_node);
2651                 khugepaged_scan.address = 0;
2652                 khugepaged_scan.mm_slot = mm_slot;
2653         }
2654         spin_unlock(&khugepaged_mm_lock);
2655
2656         mm = mm_slot->mm;
2657         down_read(&mm->mmap_sem);
2658         if (unlikely(khugepaged_test_exit(mm)))
2659                 vma = NULL;
2660         else
2661                 vma = find_vma(mm, khugepaged_scan.address);
2662
2663         progress++;
2664         for (; vma; vma = vma->vm_next) {
2665                 unsigned long hstart, hend;
2666
2667                 cond_resched();
2668                 if (unlikely(khugepaged_test_exit(mm))) {
2669                         progress++;
2670                         break;
2671                 }
2672                 if (!hugepage_vma_check(vma)) {
2673 skip:
2674                         progress++;
2675                         continue;
2676                 }
2677                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2678                 hend = vma->vm_end & HPAGE_PMD_MASK;
2679                 if (hstart >= hend)
2680                         goto skip;
2681                 if (khugepaged_scan.address > hend)
2682                         goto skip;
2683                 if (khugepaged_scan.address < hstart)
2684                         khugepaged_scan.address = hstart;
2685                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2686
2687                 while (khugepaged_scan.address < hend) {
2688                         int ret;
2689                         cond_resched();
2690                         if (unlikely(khugepaged_test_exit(mm)))
2691                                 goto breakouterloop;
2692
2693                         VM_BUG_ON(khugepaged_scan.address < hstart ||
2694                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
2695                                   hend);
2696                         ret = khugepaged_scan_pmd(mm, vma,
2697                                                   khugepaged_scan.address,
2698                                                   hpage);
2699                         /* move to next address */
2700                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2701                         progress += HPAGE_PMD_NR;
2702                         if (ret)
2703                                 /* we released mmap_sem so break loop */
2704                                 goto breakouterloop_mmap_sem;
2705                         if (progress >= pages)
2706                                 goto breakouterloop;
2707                 }
2708         }
2709 breakouterloop:
2710         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2711 breakouterloop_mmap_sem:
2712
2713         spin_lock(&khugepaged_mm_lock);
2714         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2715         /*
2716          * Release the current mm_slot if this mm is about to die, or
2717          * if we scanned all vmas of this mm.
2718          */
2719         if (khugepaged_test_exit(mm) || !vma) {
2720                 /*
2721                  * Make sure that if mm_users is reaching zero while
2722                  * khugepaged runs here, khugepaged_exit will find
2723                  * mm_slot not pointing to the exiting mm.
2724                  */
2725                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2726                         khugepaged_scan.mm_slot = list_entry(
2727                                 mm_slot->mm_node.next,
2728                                 struct mm_slot, mm_node);
2729                         khugepaged_scan.address = 0;
2730                 } else {
2731                         khugepaged_scan.mm_slot = NULL;
2732                         khugepaged_full_scans++;
2733                 }
2734
2735                 collect_mm_slot(mm_slot);
2736         }
2737
2738         return progress;
2739 }
2740
2741 static int khugepaged_has_work(void)
2742 {
2743         return !list_empty(&khugepaged_scan.mm_head) &&
2744                 khugepaged_enabled();
2745 }
2746
2747 static int khugepaged_wait_event(void)
2748 {
2749         return !list_empty(&khugepaged_scan.mm_head) ||
2750                 kthread_should_stop();
2751 }
2752
2753 static void khugepaged_do_scan(void)
2754 {
2755         struct page *hpage = NULL;
2756         unsigned int progress = 0, pass_through_head = 0;
2757         unsigned int pages = khugepaged_pages_to_scan;
2758         bool wait = true;
2759
2760         barrier(); /* write khugepaged_pages_to_scan to local stack */
2761
2762         while (progress < pages) {
2763                 if (!khugepaged_prealloc_page(&hpage, &wait))
2764                         break;
2765
2766                 cond_resched();
2767
2768                 if (unlikely(kthread_should_stop() || freezing(current)))
2769                         break;
2770
2771                 spin_lock(&khugepaged_mm_lock);
2772                 if (!khugepaged_scan.mm_slot)
2773                         pass_through_head++;
2774                 if (khugepaged_has_work() &&
2775                     pass_through_head < 2)
2776                         progress += khugepaged_scan_mm_slot(pages - progress,
2777                                                             &hpage);
2778                 else
2779                         progress = pages;
2780                 spin_unlock(&khugepaged_mm_lock);
2781         }
2782
2783         if (!IS_ERR_OR_NULL(hpage))
2784                 put_page(hpage);
2785 }
2786
2787 static void khugepaged_wait_work(void)
2788 {
2789         try_to_freeze();
2790
2791         if (khugepaged_has_work()) {
2792                 if (!khugepaged_scan_sleep_millisecs)
2793                         return;
2794
2795                 wait_event_freezable_timeout(khugepaged_wait,
2796                                              kthread_should_stop(),
2797                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
2798                 return;
2799         }
2800
2801         if (khugepaged_enabled())
2802                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2803 }
2804
2805 static int khugepaged(void *none)
2806 {
2807         struct mm_slot *mm_slot;
2808
2809         set_freezable();
2810         set_user_nice(current, MAX_NICE);
2811
2812         while (!kthread_should_stop()) {
2813                 khugepaged_do_scan();
2814                 khugepaged_wait_work();
2815         }
2816
2817         spin_lock(&khugepaged_mm_lock);
2818         mm_slot = khugepaged_scan.mm_slot;
2819         khugepaged_scan.mm_slot = NULL;
2820         if (mm_slot)
2821                 collect_mm_slot(mm_slot);
2822         spin_unlock(&khugepaged_mm_lock);
2823         return 0;
2824 }
2825
2826 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2827                 unsigned long haddr, pmd_t *pmd)
2828 {
2829         struct mm_struct *mm = vma->vm_mm;
2830         pgtable_t pgtable;
2831         pmd_t _pmd;
2832         int i;
2833
2834         pmdp_clear_flush_notify(vma, haddr, pmd);
2835         /* leave pmd empty until pte is filled */
2836
2837         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
2838         pmd_populate(mm, &_pmd, pgtable);
2839
2840         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2841                 pte_t *pte, entry;
2842                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2843                 entry = pte_mkspecial(entry);
2844                 pte = pte_offset_map(&_pmd, haddr);
2845                 VM_BUG_ON(!pte_none(*pte));
2846                 set_pte_at(mm, haddr, pte, entry);
2847                 pte_unmap(pte);
2848         }
2849         smp_wmb(); /* make pte visible before pmd */
2850         pmd_populate(mm, pmd, pgtable);
2851         put_huge_zero_page();
2852 }
2853
2854 void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
2855                 pmd_t *pmd)
2856 {
2857         spinlock_t *ptl;
2858         struct page *page;
2859         struct mm_struct *mm = vma->vm_mm;
2860         unsigned long haddr = address & HPAGE_PMD_MASK;
2861         unsigned long mmun_start;       /* For mmu_notifiers */
2862         unsigned long mmun_end;         /* For mmu_notifiers */
2863
2864         BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
2865
2866         mmun_start = haddr;
2867         mmun_end   = haddr + HPAGE_PMD_SIZE;
2868 again:
2869         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2870         ptl = pmd_lock(mm, pmd);
2871         if (unlikely(!pmd_trans_huge(*pmd))) {
2872                 spin_unlock(ptl);
2873                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2874                 return;
2875         }
2876         if (is_huge_zero_pmd(*pmd)) {
2877                 __split_huge_zero_page_pmd(vma, haddr, pmd);
2878                 spin_unlock(ptl);
2879                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2880                 return;
2881         }
2882         page = pmd_page(*pmd);
2883         VM_BUG_ON_PAGE(!page_count(page), page);
2884         get_page(page);
2885         spin_unlock(ptl);
2886         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2887
2888         split_huge_page(page);
2889
2890         put_page(page);
2891
2892         /*
2893          * We don't always have down_write of mmap_sem here: a racing
2894          * do_huge_pmd_wp_page() might have copied-on-write to another
2895          * huge page before our split_huge_page() got the anon_vma lock.
2896          */
2897         if (unlikely(pmd_trans_huge(*pmd)))
2898                 goto again;
2899 }
2900
2901 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
2902                 pmd_t *pmd)
2903 {
2904         struct vm_area_struct *vma;
2905
2906         vma = find_vma(mm, address);
2907         BUG_ON(vma == NULL);
2908         split_huge_page_pmd(vma, address, pmd);
2909 }
2910
2911 static void split_huge_page_address(struct mm_struct *mm,
2912                                     unsigned long address)
2913 {
2914         pgd_t *pgd;
2915         pud_t *pud;
2916         pmd_t *pmd;
2917
2918         VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
2919
2920         pgd = pgd_offset(mm, address);
2921         if (!pgd_present(*pgd))
2922                 return;
2923
2924         pud = pud_offset(pgd, address);
2925         if (!pud_present(*pud))
2926                 return;
2927
2928         pmd = pmd_offset(pud, address);
2929         if (!pmd_present(*pmd))
2930                 return;
2931         /*
2932          * Caller holds the mmap_sem write mode, so a huge pmd cannot
2933          * materialize from under us.
2934          */
2935         split_huge_page_pmd_mm(mm, address, pmd);
2936 }
2937
2938 void __vma_adjust_trans_huge(struct vm_area_struct *vma,
2939                              unsigned long start,
2940                              unsigned long end,
2941                              long adjust_next)
2942 {
2943         /*
2944          * If the new start address isn't hpage aligned and it could
2945          * previously contain an hugepage: check if we need to split
2946          * an huge pmd.
2947          */
2948         if (start & ~HPAGE_PMD_MASK &&
2949             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2950             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2951                 split_huge_page_address(vma->vm_mm, start);
2952
2953         /*
2954          * If the new end address isn't hpage aligned and it could
2955          * previously contain an hugepage: check if we need to split
2956          * an huge pmd.
2957          */
2958         if (end & ~HPAGE_PMD_MASK &&
2959             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2960             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2961                 split_huge_page_address(vma->vm_mm, end);
2962
2963         /*
2964          * If we're also updating the vma->vm_next->vm_start, if the new
2965          * vm_next->vm_start isn't page aligned and it could previously
2966          * contain an hugepage: check if we need to split an huge pmd.
2967          */
2968         if (adjust_next > 0) {
2969                 struct vm_area_struct *next = vma->vm_next;
2970                 unsigned long nstart = next->vm_start;
2971                 nstart += adjust_next << PAGE_SHIFT;
2972                 if (nstart & ~HPAGE_PMD_MASK &&
2973                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
2974                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
2975                         split_huge_page_address(next->vm_mm, nstart);
2976         }
2977 }