block: streamline bvec_alloc

Avoid the pointless goto by trying the slab allocation first and falling
through to the mempool.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bio.c b/block/bio.c
index c2152c4..321b347 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -172,8 +172,6 @@ static inline gfp_t bvec_alloc_gfp(gfp_t gfp)
 struct bio_vec *bvec_alloc(gfp_t gfp_mask, int nr, unsigned long *idx,
                           mempool_t *pool)
 {
-       struct bio_vec *bvl;
-
        /*
         * see comment near bvec_array define!
         */
@@ -201,28 +199,24 @@ struct bio_vec *bvec_alloc(gfp_t gfp_mask, int nr, unsigned long *idx,
        }
 
        /*
-        * idx now points to the pool we want to allocate from. only the
-        * 1-vec entry pool is mempool backed.
+        * Try a slab allocation first for all smaller allocations.  If that
+        * fails and __GFP_DIRECT_RECLAIM is set retry with the mempool.
+        * The mempool is sized to handle up to BIO_MAX_PAGES entries.
         */
-       if (*idx == BVEC_POOL_MAX) {
-fallback:
-               bvl = mempool_alloc(pool, gfp_mask);
-       } else {
+       if (*idx < BVEC_POOL_MAX) {
                struct biovec_slab *bvs = bvec_slabs + *idx;
+               struct bio_vec *bvl;
 
-               /*
-                * Try a slab allocation. If this fails and __GFP_DIRECT_RECLAIM
-                * is set, retry with the 1-entry mempool
-                */
                bvl = kmem_cache_alloc(bvs->slab, bvec_alloc_gfp(gfp_mask));
-               if (unlikely(!bvl && (gfp_mask & __GFP_DIRECT_RECLAIM))) {
-                       *idx = BVEC_POOL_MAX;
-                       goto fallback;
+               if (likely(bvl) || !(gfp_mask & __GFP_DIRECT_RECLAIM)) {
+                       (*idx)++;
+                       return bvl;
                }
+               *idx = BVEC_POOL_MAX;
        }
 
        (*idx)++;
-       return bvl;
+       return mempool_alloc(pool, gfp_mask);
 }
 
 void bio_uninit(struct bio *bio)