bio: only mempool back the largest bio_vec slab cache

We only very rarely need the mempool backing, so it makes sense to
get rid of all but one of the mempool in a bio_set. So keep the
largest bio_vec count mempool so we can always honor the largest
allocation, and "upgrade" callers that fail.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/fs/bio.c b/fs/bio.c
index df99c88..eb6b468 100644 (file)
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -58,7 +58,8 @@ unsigned int bvec_nr_vecs(unsigned short idx)
        return bvec_slabs[idx].nr_vecs;
 }
 
-struct bio_vec *bvec_alloc_bs(gfp_t gfp_mask, int nr, unsigned long *idx, struct bio_set *bs)
+struct bio_vec *bvec_alloc_bs(gfp_t gfp_mask, int nr, unsigned long *idx,
+                             struct bio_set *bs)
 {
        struct bio_vec *bvl;
 
@@ -67,60 +68,90 @@ struct bio_vec *bvec_alloc_bs(gfp_t gfp_mask, int nr, unsigned long *idx, struct
         * If not, this is a bio_kmalloc() allocation and just do a
         * kzalloc() for the exact number of vecs right away.
         */
-       if (bs) {
+       if (!bs)
+               bvl = kzalloc(nr * sizeof(struct bio_vec), gfp_mask);
+
+       /*
+        * see comment near bvec_array define!
+        */
+       switch (nr) {
+       case 1:
+               *idx = 0;
+               break;
+       case 2 ... 4:
+               *idx = 1;
+               break;
+       case 5 ... 16:
+               *idx = 2;
+               break;
+       case 17 ... 64:
+               *idx = 3;
+               break;
+       case 65 ... 128:
+               *idx = 4;
+               break;
+       case 129 ... BIO_MAX_PAGES:
+               *idx = 5;
+               break;
+       default:
+               return NULL;
+       }
+
+       /*
+        * idx now points to the pool we want to allocate from. only the
+        * 1-vec entry pool is mempool backed.
+        */
+       if (*idx == BIOVEC_MAX_IDX) {
+fallback:
+               bvl = mempool_alloc(bs->bvec_pool, gfp_mask);
+       } else {
+               struct biovec_slab *bvs = bvec_slabs + *idx;
+               gfp_t __gfp_mask = gfp_mask & ~(__GFP_WAIT | __GFP_IO);
+
                /*
-                * see comment near bvec_array define!
+                * Make this allocation restricted and don't dump info on
+                * allocation failures, since we'll fallback to the mempool
+                * in case of failure.
                 */
-               switch (nr) {
-               case 1:
-                       *idx = 0;
-                       break;
-               case 2 ... 4:
-                       *idx = 1;
-                       break;
-               case 5 ... 16:
-                       *idx = 2;
-                       break;
-               case 17 ... 64:
-                       *idx = 3;
-                       break;
-               case 65 ... 128:
-                       *idx = 4;
-                       break;
-               case 129 ... BIO_MAX_PAGES:
-                       *idx = 5;
-                       break;
-               default:
-                       return NULL;
-               }
+               __gfp_mask |= __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
 
                /*
-                * idx now points to the pool we want to allocate from
+                * Try a slab allocation. If this fails and __GFP_WAIT
+                * is set, retry with the 1-entry mempool
                 */
-               bvl = mempool_alloc(bs->bvec_pools[*idx], gfp_mask);
-               if (bvl)
-                       memset(bvl, 0,
-                               bvec_nr_vecs(*idx) * sizeof(struct bio_vec));
-       } else
-               bvl = kzalloc(nr * sizeof(struct bio_vec), gfp_mask);
+               bvl = kmem_cache_alloc(bvs->slab, __gfp_mask);
+               if (unlikely(!bvl && (gfp_mask & __GFP_WAIT))) {
+                       *idx = BIOVEC_MAX_IDX;
+                       goto fallback;
+               }
+       }
+
+       if (bvl)
+               memset(bvl, 0, bvec_nr_vecs(*idx) * sizeof(struct bio_vec));
 
        return bvl;
 }
 
-void bio_free(struct bio *bio, struct bio_set *bio_set)
+void bio_free(struct bio *bio, struct bio_set *bs)
 {
        if (bio->bi_io_vec) {
                const int pool_idx = BIO_POOL_IDX(bio);
 
                BIO_BUG_ON(pool_idx >= BIOVEC_NR_POOLS);
 
-               mempool_free(bio->bi_io_vec, bio_set->bvec_pools[pool_idx]);
+               if (pool_idx == BIOVEC_MAX_IDX)
+                       mempool_free(bio->bi_io_vec, bs->bvec_pool);
+               else {
+                       struct biovec_slab *bvs = bvec_slabs + pool_idx;
+
+                       kmem_cache_free(bvs->slab, bio->bi_io_vec);
+               }
        }
 
        if (bio_integrity(bio))
-               bio_integrity_free(bio, bio_set);
+               bio_integrity_free(bio, bs);
 
-       mempool_free(bio, bio_set->bio_pool);
+       mempool_free(bio, bs->bio_pool);
 }
 
 /*
@@ -1346,30 +1377,18 @@ EXPORT_SYMBOL(bio_sector_offset);
  */
 static int biovec_create_pools(struct bio_set *bs, int pool_entries)
 {
-       int i;
+       struct biovec_slab *bp = bvec_slabs + BIOVEC_MAX_IDX;
 
-       for (i = 0; i < BIOVEC_NR_POOLS; i++) {
-               struct biovec_slab *bp = bvec_slabs + i;
-               mempool_t **bvp = bs->bvec_pools + i;
+       bs->bvec_pool = mempool_create_slab_pool(pool_entries, bp->slab);
+       if (!bs->bvec_pool)
+               return -ENOMEM;
 
-               *bvp = mempool_create_slab_pool(pool_entries, bp->slab);
-               if (!*bvp)
-                       return -ENOMEM;
-       }
        return 0;
 }
 
 static void biovec_free_pools(struct bio_set *bs)
 {
-       int i;
-
-       for (i = 0; i < BIOVEC_NR_POOLS; i++) {
-               mempool_t *bvp = bs->bvec_pools[i];
-
-               if (bvp)
-                       mempool_destroy(bvp);
-       }
-
+       mempool_destroy(bs->bvec_pool);
 }
 
 void bioset_free(struct bio_set *bs)

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 3ed714e..d76e4bf 100644 (file)
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -397,13 +397,14 @@ static inline void bio_set_completion_cpu(struct bio *bio, unsigned int cpu)
  */
 #define BIO_POOL_SIZE 2
 #define BIOVEC_NR_POOLS 6
+#define BIOVEC_MAX_IDX (BIOVEC_NR_POOLS - 1)
 
 struct bio_set {
        mempool_t *bio_pool;
 #if defined(CONFIG_BLK_DEV_INTEGRITY)
        mempool_t *bio_integrity_pool;
 #endif
-       mempool_t *bvec_pools[BIOVEC_NR_POOLS];
+       mempool_t *bvec_pool;
 };
 
 struct biovec_slab {