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Btrfs: finish read pages in the order they are submitted

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The endio is done at reverse order of bio vectors.

That means for a sequential read, the page first submitted will finish
last in a bio. Considering we will do checksum (making cache hot) for
every page, this does introduce delay (and chance to squeeze cache used
soon) for pages submitted at the begining.

I don't observe obvious performance difference with below patch at my
simple test, but seems more natural to finish read in the order they are
submitted.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason 2010-02-03 18:18:45 +00:00
parent 0be2e98173
commit 4125bf761c
1 changed files with 4 additions and 3 deletions
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7
fs/btrfs/extent_io.c
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@ -1750,7 +1750,8 @@ static void end_bio_extent_writepage(struct bio *bio, int err)
static void end_bio_extent_readpage(struct bio *bio, int err)
{
int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
struct bio_vec *bvec_end = bio->bi_io_vec + bio->bi_vcnt - 1;
struct bio_vec *bvec = bio->bi_io_vec;
struct extent_io_tree *tree;
u64 start;
u64 end;
@ -1773,7 +1774,7 @@ static void end_bio_extent_readpage(struct bio *bio, int err)
else
whole_page = 0;
if (--bvec >= bio->bi_io_vec)
if (++bvec <= bvec_end)
prefetchw(&bvec->bv_page->flags);
if (uptodate && tree->ops && tree->ops->readpage_end_io_hook) {
@ -1818,7 +1819,7 @@ static void end_bio_extent_readpage(struct bio *bio, int err)
}
check_page_locked(tree, page);
}
} while (bvec >= bio->bi_io_vec);
} while (bvec <= bvec_end);
bio_put(bio);
}