dm: store dm_target_io in bio front_pad

Use the recently-added bio front_pad field to allocate struct dm_target_io.

Prior to this patch, dm_target_io was allocated from a mempool. For each
dm_target_io, there is exactly one bio allocated from a bioset.

This patch merges these two allocations into one allocation: we create a
bioset with front_pad equal to the size of dm_target_io so that every
bio allocated from the bioset has sizeof(struct dm_target_io) bytes
before it. We allocate a bio and use the bytes before the bio as
dm_target_io.

_tio_cache is removed and the tio_pool mempool is now only used for
request-based devices.

This idea was introduced by Kent Overstreet.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: tj@kernel.org
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Bill Pemberton <wfp5p@viridian.itc.virginia.edu>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 49 insertions, 59 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 66ceaff6455c..02db9183ca01 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -71,6 +71,7 @@ struct dm_target_io {
         struct dm_io *io;
         struct dm_target *ti;
         union map_info info;
+        struct bio clone;
 };
 
 /*
@@ -214,7 +215,6 @@ struct dm_md_mempools {
 
 #define MIN_IOS 256
 static struct kmem_cache *_io_cache;
-static struct kmem_cache *_tio_cache;
 static struct kmem_cache *_rq_tio_cache;
 
 /*
@@ -232,14 +232,9 @@ static int __init local_init(void)
         if (!_io_cache)
                 return r;
 
-        /* allocate a slab for the target ios */
-        _tio_cache = KMEM_CACHE(dm_target_io, 0);
-        if (!_tio_cache)
-                goto out_free_io_cache;
-
         _rq_tio_cache = KMEM_CACHE(dm_rq_target_io, 0);
         if (!_rq_tio_cache)
-                goto out_free_tio_cache;
+                goto out_free_io_cache;
 
         _rq_bio_info_cache = KMEM_CACHE(dm_rq_clone_bio_info, 0);
         if (!_rq_bio_info_cache)
@@ -265,8 +260,6 @@ out_free_rq_bio_info_cache:
         kmem_cache_destroy(_rq_bio_info_cache);
 out_free_rq_tio_cache:
         kmem_cache_destroy(_rq_tio_cache);
-out_free_tio_cache:
-        kmem_cache_destroy(_tio_cache);
 out_free_io_cache:
         kmem_cache_destroy(_io_cache);
 
@@ -277,7 +270,6 @@ static void local_exit(void)
 {
         kmem_cache_destroy(_rq_bio_info_cache);
         kmem_cache_destroy(_rq_tio_cache);
-        kmem_cache_destroy(_tio_cache);
         kmem_cache_destroy(_io_cache);
         unregister_blkdev(_major, _name);
         dm_uevent_exit();
@@ -463,7 +455,7 @@ static void free_io(struct mapped_device *md, struct dm_io *io)
 
 static void free_tio(struct mapped_device *md, struct dm_target_io *tio)
 {
-        mempool_free(tio, md->tio_pool);
+        bio_put(&tio->clone);
 }
 
 static struct dm_rq_target_io *alloc_rq_tio(struct mapped_device *md,
@@ -682,7 +674,6 @@ static void clone_endio(struct bio *bio, int error)
         }
 
         free_tio(md, tio);
-        bio_put(bio);
         dec_pending(io, error);
 }
 
@@ -1002,12 +993,12 @@ int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)
 }
 EXPORT_SYMBOL_GPL(dm_set_target_max_io_len);
 
-static void __map_bio(struct dm_target *ti, struct bio *clone,
-                      struct dm_target_io *tio)
+static void __map_bio(struct dm_target *ti, struct dm_target_io *tio)
 {
         int r;
         sector_t sector;
         struct mapped_device *md;
+        struct bio *clone = &tio->clone;
 
         clone->bi_end_io = clone_endio;
         clone->bi_private = tio;
@@ -1031,7 +1022,6 @@ static void __map_bio(struct dm_target *ti, struct bio *clone,
                 /* error the io and bail out, or requeue it if needed */
                 md = tio->io->md;
                 dec_pending(tio->io, r);
-                bio_put(clone);
                 free_tio(md, tio);
         } else if (r) {
                 DMWARN("unimplemented target map return value: %d", r);
@@ -1052,14 +1042,13 @@ struct clone_info {
 /*
  * Creates a little bio that just does part of a bvec.
  */
-static struct bio *split_bvec(struct bio *bio, sector_t sector,
-                              unsigned short idx, unsigned int offset,
-                              unsigned int len, struct bio_set *bs)
+static void split_bvec(struct dm_target_io *tio, struct bio *bio,
+                       sector_t sector, unsigned short idx, unsigned int offset,
+                       unsigned int len, struct bio_set *bs)
 {
-        struct bio *clone;
+        struct bio *clone = &tio->clone;
         struct bio_vec *bv = bio->bi_io_vec + idx;
 
-        clone = bio_alloc_bioset(GFP_NOIO, 1, bs);
         *clone->bi_io_vec = *bv;
 
         clone->bi_sector = sector;
@@ -1076,20 +1065,18 @@ static struct bio *split_bvec(struct bio *bio, sector_t sector,
                 bio_integrity_trim(clone,
                                    bio_sector_offset(bio, idx, offset), len);
         }
-
-        return clone;
 }
 
 /*
  * Creates a bio that consists of range of complete bvecs.
  */
-static struct bio *clone_bio(struct bio *bio, sector_t sector,
-                             unsigned short idx, unsigned short bv_count,
-                             unsigned int len, struct bio_set *bs)
+static void clone_bio(struct dm_target_io *tio, struct bio *bio,
+                      sector_t sector, unsigned short idx,
+                      unsigned short bv_count, unsigned int len,
+                      struct bio_set *bs)
 {
-        struct bio *clone;
+        struct bio *clone = &tio->clone;
 
-        clone = bio_alloc_bioset(GFP_NOIO, bio->bi_max_vecs, bs);
         __bio_clone(clone, bio);
         clone->bi_sector = sector;
         clone->bi_idx = idx;
@@ -1104,14 +1091,16 @@ static struct bio *clone_bio(struct bio *bio, sector_t sector,
                         bio_integrity_trim(clone,
                                            bio_sector_offset(bio, idx, 0), len);
         }
-
-        return clone;
 }
 
 static struct dm_target_io *alloc_tio(struct clone_info *ci,
-                                      struct dm_target *ti)
+                                      struct dm_target *ti, int nr_iovecs)
 {
-        struct dm_target_io *tio = mempool_alloc(ci->md->tio_pool, GFP_NOIO);
+        struct dm_target_io *tio;
+        struct bio *clone;
+
+        clone = bio_alloc_bioset(GFP_NOIO, nr_iovecs, ci->md->bs);
+        tio = container_of(clone, struct dm_target_io, clone);
 
         tio->io = ci->io;
         tio->ti = ti;
@@ -1123,8 +1112,8 @@ static struct dm_target_io *alloc_tio(struct clone_info *ci,
 static void __issue_target_request(struct clone_info *ci, struct dm_target *ti,
                                    unsigned request_nr, sector_t len)
 {
-        struct dm_target_io *tio = alloc_tio(ci, ti);
-        struct bio *clone;
+        struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs);
+        struct bio *clone = &tio->clone;
 
         tio->info.target_request_nr = request_nr;
 
@@ -1133,14 +1122,14 @@ static void __issue_target_request(struct clone_info *ci, struct dm_target *ti,
          * ci->bio->bi_max_vecs is BIO_INLINE_VECS anyway, for both flush
          * and discard, so no need for concern about wasted bvec allocations.
          */
-        clone = bio_clone_bioset(ci->bio, GFP_NOIO, ci->md->bs);
 
+         __bio_clone(clone, ci->bio);
         if (len) {
                 clone->bi_sector = ci->sector;
                 clone->bi_size = to_bytes(len);
         }
 
-        __map_bio(ti, clone, tio);
+        __map_bio(ti, tio);
 }
 
 static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
@@ -1169,14 +1158,13 @@ static int __clone_and_map_empty_flush(struct clone_info *ci)
  */
 static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti)
 {
-        struct bio *clone, *bio = ci->bio;
+        struct bio *bio = ci->bio;
         struct dm_target_io *tio;
 
-        tio = alloc_tio(ci, ti);
-        clone = clone_bio(bio, ci->sector, ci->idx,
-                          bio->bi_vcnt - ci->idx, ci->sector_count,
-                          ci->md->bs);
-        __map_bio(ti, clone, tio);
+        tio = alloc_tio(ci, ti, bio->bi_max_vecs);
+        clone_bio(tio, bio, ci->sector, ci->idx, bio->bi_vcnt - ci->idx,
+                  ci->sector_count, ci->md->bs);
+        __map_bio(ti, tio);
         ci->sector_count = 0;
 }
 
@@ -1214,7 +1202,7 @@ static int __clone_and_map_discard(struct clone_info *ci)
 
 static int __clone_and_map(struct clone_info *ci)
 {
-        struct bio *clone, *bio = ci->bio;
+        struct bio *bio = ci->bio;
         struct dm_target *ti;
         sector_t len = 0, max;
         struct dm_target_io *tio;
@@ -1254,10 +1242,10 @@ static int __clone_and_map(struct clone_info *ci)
                         len += bv_len;
                 }
 
-                tio = alloc_tio(ci, ti);
-                clone = clone_bio(bio, ci->sector, ci->idx, i - ci->idx, len,
-                                  ci->md->bs);
-                __map_bio(ti, clone, tio);
+                tio = alloc_tio(ci, ti, bio->bi_max_vecs);
+                clone_bio(tio, bio, ci->sector, ci->idx, i - ci->idx, len,
+                          ci->md->bs);
+                __map_bio(ti, tio);
 
                 ci->sector += len;
                 ci->sector_count -= len;
@@ -1282,12 +1270,11 @@ static int __clone_and_map(struct clone_info *ci)
 
                         len = min(remaining, max);
 
-                        tio = alloc_tio(ci, ti);
-                        clone = split_bvec(bio, ci->sector, ci->idx,
-                                           bv->bv_offset + offset, len,
-                                           ci->md->bs);
+                        tio = alloc_tio(ci, ti, 1);
+                        split_bvec(tio, bio, ci->sector, ci->idx,
+                                   bv->bv_offset + offset, len, ci->md->bs);
 
-                        __map_bio(ti, clone, tio);
+                        __map_bio(ti, tio);
 
                         ci->sector += len;
                         ci->sector_count -= len;
@@ -1955,7 +1942,7 @@ static void __bind_mempools(struct mapped_device *md, struct dm_table *t)
 {
         struct dm_md_mempools *p;
 
-        if (md->io_pool && md->tio_pool && md->bs)
+        if (md->io_pool && (md->tio_pool || dm_table_get_type(t) == DM_TYPE_BIO_BASED) && md->bs)
                 /* the md already has necessary mempools */
                 goto out;
 
@@ -2732,14 +2719,16 @@ struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity)
         if (!pools->io_pool)
                 goto free_pools_and_out;
 
-        pools->tio_pool = (type == DM_TYPE_BIO_BASED) ?
-                          mempool_create_slab_pool(MIN_IOS, _tio_cache) :
-                          mempool_create_slab_pool(MIN_IOS, _rq_tio_cache);
-        if (!pools->tio_pool)
-                goto free_io_pool_and_out;
+        pools->tio_pool = NULL;
+        if (type == DM_TYPE_REQUEST_BASED) {
+                pools->tio_pool = mempool_create_slab_pool(MIN_IOS, _rq_tio_cache);
+                if (!pools->tio_pool)
+                        goto free_io_pool_and_out;
+        }
 
         pools->bs = (type == DM_TYPE_BIO_BASED) ?
-                bioset_create(pool_size, 0) :
+                bioset_create(pool_size,
+                              offsetof(struct dm_target_io, clone)) :
                 bioset_create(pool_size,
                               offsetof(struct dm_rq_clone_bio_info, clone));
         if (!pools->bs)
@@ -2754,7 +2743,8 @@ free_bioset_and_out:
         bioset_free(pools->bs);
 
 free_tio_pool_and_out:
-        mempool_destroy(pools->tio_pool);
+        if (pools->tio_pool)
+                mempool_destroy(pools->tio_pool);
 
 free_io_pool_and_out:
         mempool_destroy(pools->io_pool);