block: blk-merge: fast-clone bio when splitting rw bios
authorMing Lei <ming.lei@canonical.com>
Thu, 17 Sep 2015 15:58:38 +0000 (09:58 -0600)
committerJens Axboe <axboe@fb.com>
Thu, 17 Sep 2015 15:58:38 +0000 (09:58 -0600)
biovecs has become immutable since v3.13, so it isn't necessary
to allocate biovecs for the new cloned bios, then we can save
one extra biovecs allocation/copy, and the allocation is often
not fixed-length and a bit more expensive.

For example, if the 'max_sectors_kb' of null blk's queue is set
as 16(32 sectors) via sysfs just for making more splits, this patch
can increase throught about ~70% in the sequential read test over
null_blk(direct io, bs: 1M).

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Ming Lin <ming.l@ssi.samsung.com>
Cc: Dongsu Park <dpark@posteo.net>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
This fixes a performance regression introduced by commit 54efd50bfd,
and allows us to take full advantage of the fact that we have immutable
bio_vecs. Hand applied, as it rejected violently with commit
5014c311baa2.

Signed-off-by: Jens Axboe <axboe@fb.com>
block/blk-merge.c

index 574ea7c0468ffa7657153af75c7057e8cf5f6cff..c4e9c37f3e38122e5125502d62ab1ddd2e887408 100644 (file)
@@ -66,15 +66,12 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
                                         struct bio *bio,
                                         struct bio_set *bs)
 {
-       struct bio *split;
        struct bio_vec bv, bvprv, *bvprvp = NULL;
        struct bvec_iter iter;
        unsigned seg_size = 0, nsegs = 0, sectors = 0;
 
        bio_for_each_segment(bv, bio, iter) {
-               sectors += bv.bv_len >> 9;
-
-               if (sectors > queue_max_sectors(q))
+               if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q))
                        goto split;
 
                /*
@@ -95,6 +92,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
                        seg_size += bv.bv_len;
                        bvprv = bv;
                        bvprvp = &bv;
+                       sectors += bv.bv_len >> 9;
                        continue;
                }
 new_segment:
@@ -105,21 +103,12 @@ new_segment:
                bvprv = bv;
                bvprvp = &bv;
                seg_size = bv.bv_len;
+               sectors += bv.bv_len >> 9;
        }
 
        return NULL;
 split:
-       split = bio_clone_bioset(bio, GFP_NOIO, bs);
-
-       split->bi_iter.bi_size -= iter.bi_size;
-       bio->bi_iter = iter;
-
-       if (bio_integrity(bio)) {
-               bio_integrity_advance(bio, split->bi_iter.bi_size);
-               bio_integrity_trim(split, 0, bio_sectors(split));
-       }
-
-       return split;
+       return bio_split(bio, sectors, GFP_NOIO, bs);
 }
 
 void blk_queue_split(struct request_queue *q, struct bio **bio,