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>
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 895795c..247b17f 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -469,26 +469,17 @@
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++;
}
