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block: rewrite blk_bvec_map_sg to avoid a nth_page call 

The offset in scatterlists is allowed to be larger than the page size,
so don't go to great length to avoid that case and simplify the
arithmetics.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2019-04-11 08:23:27 +02:00 committed by Jens Axboe
parent 22391ac30a
commit 8a96a0e408
1 changed files with 6 additions and 15 deletions
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21
block/blk-merge.c
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@ -469,26 +469,17 @@ static unsigned blk_bvec_map_sg(struct request_queue *q,
struct scatterlist **sg)
{
unsigned nbytes = bvec->bv_len;
unsigned nsegs = 0, total = 0, offset = 0;
unsigned nsegs = 0, total = 0;
while (nbytes > 0) {
unsigned seg_size;
struct page *pg;
unsigned idx;
unsigned offset = bvec->bv_offset + total;
unsigned len = min(get_max_segment_size(q, offset), nbytes);
*sg = blk_next_sg(sg, sglist);
sg_set_page(*sg, bvec->bv_page, len, offset);
seg_size = get_max_segment_size(q, bvec->bv_offset + total);
seg_size = min(nbytes, seg_size);
offset = (total + bvec->bv_offset) % PAGE_SIZE;
idx = (total + bvec->bv_offset) / PAGE_SIZE;
pg = bvec_nth_page(bvec->bv_page, idx);
sg_set_page(*sg, pg, seg_size, offset);
total += seg_size;
nbytes -= seg_size;
total += len;
nbytes -= len;
nsegs++;
}