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Btrfs: finish read pages in the order they are submitted
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>
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4125bf761c
@ -1750,7 +1750,8 @@ static void end_bio_extent_writepage(struct bio *bio, int err)
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static void end_bio_extent_readpage(struct bio *bio, int err)
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{
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int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
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struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
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struct bio_vec *bvec_end = bio->bi_io_vec + bio->bi_vcnt - 1;
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struct bio_vec *bvec = bio->bi_io_vec;
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struct extent_io_tree *tree;
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u64 start;
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u64 end;
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@ -1773,7 +1774,7 @@ static void end_bio_extent_readpage(struct bio *bio, int err)
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else
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whole_page = 0;
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if (--bvec >= bio->bi_io_vec)
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if (++bvec <= bvec_end)
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prefetchw(&bvec->bv_page->flags);
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if (uptodate && tree->ops && tree->ops->readpage_end_io_hook) {
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@ -1818,7 +1819,7 @@ static void end_bio_extent_readpage(struct bio *bio, int err)
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}
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check_page_locked(tree, page);
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}
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} while (bvec >= bio->bi_io_vec);
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} while (bvec <= bvec_end);
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bio_put(bio);
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}
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