mm/highmem.c

   1 /*
   2  * High memory handling common code and variables.
   3  *
   4  * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
   5  *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
   6  *
   7  *
   8  * Redesigned the x86 32-bit VM architecture to deal with
   9  * 64-bit physical space. With current x86 CPUs this
  10  * means up to 64 Gigabytes physical RAM.
  11  *
  12  * Rewrote high memory support to move the page cache into
  13  * high memory. Implemented permanent (schedulable) kmaps
  14  * based on Linus' idea.
  15  *
  16  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
  17  */
  18
  19 #include <linux/mm.h>
  20 #include <linux/module.h>
  21 #include <linux/swap.h>
  22 #include <linux/bio.h>
  23 #include <linux/pagemap.h>
  24 #include <linux/mempool.h>
  25 #include <linux/blkdev.h>
  26 #include <linux/init.h>
  27 #include <linux/hash.h>
  28 #include <linux/highmem.h>
  29 #include <linux/blktrace_api.h>
  30 #include <asm/tlbflush.h>
  31
  32 /*
  33  * Virtual_count is not a pure "count".
  34  *  0 means that it is not mapped, and has not been mapped
  35  *    since a TLB flush - it is usable.
  36  *  1 means that there are no users, but it has been mapped
  37  *    since the last TLB flush - so we can't use it.
  38  *  n means that there are (n-1) current users of it.
  39  */
  40 #ifdef CONFIG_HIGHMEM
  41
  42 unsigned long totalhigh_pages __read_mostly;
  43
  44 unsigned int nr_free_highpages (void)
  45 {
  46         pg_data_t *pgdat;
  47         unsigned int pages = 0;
  48
  49         for_each_online_pgdat(pgdat)
  50                 pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
  51                         NR_FREE_PAGES);
  52
  53         return pages;
  54 }
  55
  56 static int pkmap_count[LAST_PKMAP];
  57 static unsigned int last_pkmap_nr;
  58 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
  59
  60 pte_t * pkmap_page_table;
  61
  62 static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
  63
  64 static void flush_all_zero_pkmaps(void)
  65 {
  66         int i;
  67
  68         flush_cache_kmaps();
  69
  70         for (i = 0; i < LAST_PKMAP; i++) {
  71                 struct page *page;
  72
  73                 /*
  74                  * zero means we don't have anything to do,
  75                  * >1 means that it is still in use. Only
  76                  * a count of 1 means that it is free but
  77                  * needs to be unmapped
  78                  */
  79                 if (pkmap_count[i] != 1)
  80                         continue;
  81                 pkmap_count[i] = 0;
  82
  83                 /* sanity check */
  84                 BUG_ON(pte_none(pkmap_page_table[i]));
  85
  86                 /*
  87                  * Don't need an atomic fetch-and-clear op here;
  88                  * no-one has the page mapped, and cannot get at
  89                  * its virtual address (and hence PTE) without first
  90                  * getting the kmap_lock (which is held here).
  91                  * So no dangers, even with speculative execution.
  92                  */
  93                 page = pte_page(pkmap_page_table[i]);
  94                 pte_clear(&init_mm, (unsigned long)page_address(page),
  95                           &pkmap_page_table[i]);
  96
  97                 set_page_address(page, NULL);
  98         }
  99         flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 100 }
 101
 102 static inline unsigned long map_new_virtual(struct page *page)
 103 {
 104         unsigned long vaddr;
 105         int count;
 106
 107 start:
 108         count = LAST_PKMAP;
 109         /* Find an empty entry */
 110         for (;;) {
 111                 last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
 112                 if (!last_pkmap_nr) {
 113                         flush_all_zero_pkmaps();
 114                         count = LAST_PKMAP;
 115                 }
 116                 if (!pkmap_count[last_pkmap_nr])
 117                         break;  /* Found a usable entry */
 118                 if (--count)
 119                         continue;
 120
 121                 /*
 122                  * Sleep for somebody else to unmap their entries
 123                  */
 124                 {
 125                         DECLARE_WAITQUEUE(wait, current);
 126
 127                         __set_current_state(TASK_UNINTERRUPTIBLE);
 128                         add_wait_queue(&pkmap_map_wait, &wait);
 129                         spin_unlock(&kmap_lock);
 130                         schedule();
 131                         remove_wait_queue(&pkmap_map_wait, &wait);
 132                         spin_lock(&kmap_lock);
 133
 134                         /* Somebody else might have mapped it while we slept */
 135                         if (page_address(page))
 136                                 return (unsigned long)page_address(page);
 137
 138                         /* Re-start */
 139                         goto start;
 140                 }
 141         }
 142         vaddr = PKMAP_ADDR(last_pkmap_nr);
 143         set_pte_at(&init_mm, vaddr,
 144                    &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
 145
 146         pkmap_count[last_pkmap_nr] = 1;
 147         set_page_address(page, (void *)vaddr);
 148
 149         return vaddr;
 150 }
 151
 152 void fastcall *kmap_high(struct page *page)
 153 {
 154         unsigned long vaddr;
 155
 156         /*
 157          * For highmem pages, we can't trust "virtual" until
 158          * after we have the lock.
 159          *
 160          * We cannot call this from interrupts, as it may block
 161          */
 162         spin_lock(&kmap_lock);
 163         vaddr = (unsigned long)page_address(page);
 164         if (!vaddr)
 165                 vaddr = map_new_virtual(page);
 166         pkmap_count[PKMAP_NR(vaddr)]++;
 167         BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
 168         spin_unlock(&kmap_lock);
 169         return (void*) vaddr;
 170 }
 171
 172 EXPORT_SYMBOL(kmap_high);
 173
 174 void fastcall kunmap_high(struct page *page)
 175 {
 176         unsigned long vaddr;
 177         unsigned long nr;
 178         int need_wakeup;
 179
 180         spin_lock(&kmap_lock);
 181         vaddr = (unsigned long)page_address(page);
 182         BUG_ON(!vaddr);
 183         nr = PKMAP_NR(vaddr);
 184
 185         /*
 186          * A count must never go down to zero
 187          * without a TLB flush!
 188          */
 189         need_wakeup = 0;
 190         switch (--pkmap_count[nr]) {
 191         case 0:
 192                 BUG();
 193         case 1:
 194                 /*
 195                  * Avoid an unnecessary wake_up() function call.
 196                  * The common case is pkmap_count[] == 1, but
 197                  * no waiters.
 198                  * The tasks queued in the wait-queue are guarded
 199                  * by both the lock in the wait-queue-head and by
 200                  * the kmap_lock.  As the kmap_lock is held here,
 201                  * no need for the wait-queue-head's lock.  Simply
 202                  * test if the queue is empty.
 203                  */
 204                 need_wakeup = waitqueue_active(&pkmap_map_wait);
 205         }
 206         spin_unlock(&kmap_lock);
 207
 208         /* do wake-up, if needed, race-free outside of the spin lock */
 209         if (need_wakeup)
 210                 wake_up(&pkmap_map_wait);
 211 }
 212
 213 EXPORT_SYMBOL(kunmap_high);
 214 #endif
 215
 216 #if defined(HASHED_PAGE_VIRTUAL)
 217
 218 #define PA_HASH_ORDER   7
 219
 220 /*
 221  * Describes one page->virtual association
 222  */
 223 struct page_address_map {
 224         struct page *page;
 225         void *virtual;
 226         struct list_head list;
 227 };
 228
 229 /*
 230  * page_address_map freelist, allocated from page_address_maps.
 231  */
 232 static struct list_head page_address_pool;      /* freelist */
 233 static spinlock_t pool_lock;                    /* protects page_address_pool */
 234
 235 /*
 236  * Hash table bucket
 237  */
 238 static struct page_address_slot {
 239         struct list_head lh;                    /* List of page_address_maps */
 240         spinlock_t lock;                        /* Protect this bucket's list */
 241 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
 242
 243 static struct page_address_slot *page_slot(struct page *page)
 244 {
 245         return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
 246 }
 247
 248 void *page_address(struct page *page)
 249 {
 250         unsigned long flags;
 251         void *ret;
 252         struct page_address_slot *pas;
 253
 254         if (!PageHighMem(page))
 255                 return lowmem_page_address(page);
 256
 257         pas = page_slot(page);
 258         ret = NULL;
 259         spin_lock_irqsave(&pas->lock, flags);
 260         if (!list_empty(&pas->lh)) {
 261                 struct page_address_map *pam;
 262
 263                 list_for_each_entry(pam, &pas->lh, list) {
 264                         if (pam->page == page) {
 265                                 ret = pam->virtual;
 266                                 goto done;
 267                         }
 268                 }
 269         }
 270 done:
 271         spin_unlock_irqrestore(&pas->lock, flags);
 272         return ret;
 273 }
 274
 275 EXPORT_SYMBOL(page_address);
 276
 277 void set_page_address(struct page *page, void *virtual)
 278 {
 279         unsigned long flags;
 280         struct page_address_slot *pas;
 281         struct page_address_map *pam;
 282
 283         BUG_ON(!PageHighMem(page));
 284
 285         pas = page_slot(page);
 286         if (virtual) {          /* Add */
 287                 BUG_ON(list_empty(&page_address_pool));
 288
 289                 spin_lock_irqsave(&pool_lock, flags);
 290                 pam = list_entry(page_address_pool.next,
 291                                 struct page_address_map, list);
 292                 list_del(&pam->list);
 293                 spin_unlock_irqrestore(&pool_lock, flags);
 294
 295                 pam->page = page;
 296                 pam->virtual = virtual;
 297
 298                 spin_lock_irqsave(&pas->lock, flags);
 299                 list_add_tail(&pam->list, &pas->lh);
 300                 spin_unlock_irqrestore(&pas->lock, flags);
 301         } else {                /* Remove */
 302                 spin_lock_irqsave(&pas->lock, flags);
 303                 list_for_each_entry(pam, &pas->lh, list) {
 304                         if (pam->page == page) {
 305                                 list_del(&pam->list);
 306                                 spin_unlock_irqrestore(&pas->lock, flags);
 307                                 spin_lock_irqsave(&pool_lock, flags);
 308                                 list_add_tail(&pam->list, &page_address_pool);
 309                                 spin_unlock_irqrestore(&pool_lock, flags);
 310                                 goto done;
 311                         }
 312                 }
 313                 spin_unlock_irqrestore(&pas->lock, flags);
 314         }
 315 done:
 316         return;
 317 }
 318
 319 static struct page_address_map page_address_maps[LAST_PKMAP];
 320
 321 void __init page_address_init(void)
 322 {
 323         int i;
 324
 325         INIT_LIST_HEAD(&page_address_pool);
 326         for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
 327                 list_add(&page_address_maps[i].list, &page_address_pool);
 328         for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
 329                 INIT_LIST_HEAD(&page_address_htable[i].lh);
 330                 spin_lock_init(&page_address_htable[i].lock);
 331         }
 332         spin_lock_init(&pool_lock);
 333 }
 334
 335 #endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */