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由 Ming Lei 提交于
Commit 729204ef("block: relax check on sg gap") allows us to merge bios, if both are physically contiguous. This change can merge a huge number of small bios, through mkfs for example, mkfs.ntfs running time can be decreased to ~1/10. But if one rq starts with a non-aligned buffer (the 1st bvec's bv_offset is non-zero) and if we allow the merge, it is quite difficult to respect sg gap limit, especially the max segment size, or we risk having an unaligned virtual boundary. This patch tries to avoid the issue by disallowing a merge, if the req starts with an unaligned buffer. Also add comments to explain why the merged segment can't end in unaligned virt boundary. Fixes: 729204ef ("block: relax check on sg gap") Tested-by: NJohannes Thumshirn <jthumshirn@suse.de> Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de> Signed-off-by: NMing Lei <ming.lei@redhat.com> Rewrote parts of the commit message and comments. Signed-off-by: NJens Axboe <axboe@fb.com>
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