[PATCH 3/6] block: don't allocate inline bvecs if this bioset needn't bvecs

[Ming Lei]

The inline bvecs won't be used if user needn't bvecs by not passing
BIOSET_NEED_BVECS, so don't allocate bvecs in this situation.

Signed-off-by: Ming Lei <ming....@redhat.com>
---
 block/bio.c         | 11 +++++++----
 include/linux/bio.h |  1 +
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index aa657cdd7c8c..3991a5aab1bc 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -110,7 +110,7 @@ static void bio_put_slab(struct bio_set *bs)
 {
        struct bio_slab *bslab = NULL;
        unsigned int slab_size = bs->front_pad + sizeof(struct bio) +
-               BIO_INLINE_VECS * sizeof(struct bio_vec);
+               bs->back_pad;
 
        mutex_lock(&bio_slab_lock);
 
@@ -1567,15 +1567,18 @@ int bioset_init(struct bio_set *bs,
                unsigned int front_pad,
                int flags)
 {
-       unsigned int back_pad = BIO_INLINE_VECS * sizeof(struct bio_vec);
-
        bs->front_pad = front_pad;
 
+       if (flags & BIOSET_NEED_BVECS)
+               bs->back_pad = BIO_INLINE_VECS * sizeof(struct bio_vec);
+       else
+               bs->back_pad = 0;
+
        spin_lock_init(&bs->rescue_lock);
        bio_list_init(&bs->rescue_list);
        INIT_WORK(&bs->rescue_work, bio_alloc_rescue);
 
-       bs->bio_slab = bio_find_or_create_slab(front_pad + back_pad);
+       bs->bio_slab = bio_find_or_create_slab(bs->front_pad + bs->back_pad);
        if (!bs->bio_slab)
                return -ENOMEM;
 
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 1edda614f7ce..f606eb1e556f 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -703,6 +703,7 @@ struct bio_set {
        mempool_t bvec_integrity_pool;
 #endif
 
+       unsigned int back_pad;
        /*
         * Deadlock avoidance for stacking block drivers: see comments in
         * bio_alloc_bioset() for details
-- 
2.28.0