block: use bio_clone_fast() in blk_rq_prep_clone()

Request cloning clones bios in the request to track the completion
of each bio.
For that purpose, we can use bio_clone_fast() instead of bio_clone()
to avoid unnecessary allocation and copy of bvecs.

This patch reduces memory footprint of request-based device-mapper
(about 1-4KB for each request) and is a preparation for further
reduction of memory usage by removing unused bvec mempool.

Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-core.c b/block/blk-core.c
index 4aa9ccd02a509b644a5c0c6e551b1aabd53f28f5..ffcb47af35f3e0d8834299edb1e6e84084ba23d3 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2926,7 +2926,7 @@ int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
        blk_rq_init(NULL, rq);
 
        __rq_for_each_bio(bio_src, rq_src) {
-               bio = bio_clone_bioset(bio_src, gfp_mask, bs);
+               bio = bio_clone_fast(bio_src, gfp_mask, bs);
                if (!bio)
                        goto free_and_out;