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block: optimize bvec iteration in bvec_iter_advance 

There is no need to only iterate in chunks of PAGE_SIZE or less in
bvec_iter_advance, given that the callers pass in the chunk length that
they are operating on - either that already is less than PAGE_SIZE
because they do classic page-based iteration, or it is larger because
the caller operates on multi-page bvecs.

This should help shaving off a few cycles of the I/O hot path.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2019-02-28 11:00:18 -05:00 committed by Jens Axboe
parent 594b9a89af
commit 5b88a17cfd
1 changed files with 4 additions and 3 deletions
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7
include/linux/bvec.h
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@ -112,14 +112,15 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
}
while (bytes) {
unsigned iter_len = bvec_iter_len(bv, *iter);
unsigned len = min(bytes, iter_len);
const struct bio_vec *cur = bv + iter->bi_idx;
unsigned len = min3(bytes, iter->bi_size,
cur->bv_len - iter->bi_bvec_done);
bytes -= len;
iter->bi_size -= len;
iter->bi_bvec_done += len;
if (iter->bi_bvec_done == __bvec_iter_bvec(bv, *iter)->bv_len) {
if (iter->bi_bvec_done == cur->bv_len) {
iter->bi_bvec_done = 0;
iter->bi_idx++;
}