block: enable bio caching use for passthru IO

bdev based polled O_DIRECT is currently quite a bit faster than
passthru on the same device, and one of the reaons is that we're not
able to use the bio caching for passthru IO.

If REQ_POLLED is set on the request, use the fs bio set for grabbing a
bio from the caches, if available. This saves 5-6% of CPU over head
for polled passthru IO.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-map.c b/block/blk-map.c
index 379c52d..16153fd 100644 (file)
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -231,6 +231,16 @@ out_bmd:
        return ret;
 }
 
+static void bio_map_put(struct bio *bio)
+{
+       if (bio->bi_opf & REQ_ALLOC_CACHE) {
+               bio_put(bio);
+       } else {
+               bio_uninit(bio);
+               kfree(bio);
+       }
+}
+
 static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
                gfp_t gfp_mask)
 {
@@ -243,10 +253,19 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
        if (!iov_iter_count(iter))
                return -EINVAL;
 
-       bio = bio_kmalloc(nr_vecs, gfp_mask);
-       if (!bio)
-               return -ENOMEM;
-       bio_init(bio, NULL, bio->bi_inline_vecs, nr_vecs, req_op(rq));
+       if (rq->cmd_flags & REQ_POLLED) {
+               blk_opf_t opf = rq->cmd_flags | REQ_ALLOC_CACHE;
+
+               bio = bio_alloc_bioset(NULL, nr_vecs, opf, gfp_mask,
+                                       &fs_bio_set);
+               if (!bio)
+                       return -ENOMEM;
+       } else {
+               bio = bio_kmalloc(nr_vecs, gfp_mask);
+               if (!bio)
+                       return -ENOMEM;
+               bio_init(bio, NULL, bio->bi_inline_vecs, nr_vecs, req_op(rq));
+       }
 
        while (iov_iter_count(iter)) {
                struct page **pages;
@@ -305,8 +324,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 
  out_unmap:
        bio_release_pages(bio, false);
-       bio_uninit(bio);
-       kfree(bio);
+       bio_map_put(bio);
        return ret;
 }
 
@@ -611,8 +629,7 @@ int blk_rq_unmap_user(struct bio *bio)
 
                next_bio = bio;
                bio = bio->bi_next;
-               bio_uninit(next_bio);
-               kfree(next_bio);
+               bio_map_put(next_bio);
        }
 
        return ret;