block: rewrite blk_bvec_map_sg to avoid a nth_page call (8a96a0e4) · Commits · 戴 / test

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>

block/blk-merge.c

+6 −15

Original line number	Diff line number	Diff line
		@@ -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++;
		}

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