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.

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>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 66ceaff6455c9dec8de3680cb7ececc49bef896f..8cdc108ef67dfa7d8322f968b530a0c7ae3ae834 100644 (file)
--- 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;
 };
 
 /*
@@ -463,7 +464,7 @@ 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 +683,6 @@ static void clone_endio(struct bio *bio, int error)
        }
 
        free_tio(md, tio);
-       bio_put(bio);
        dec_pending(io, error);
 }
 
@@ -1002,12 +1002,12 @@ 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 +1031,6 @@ 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 +1051,13 @@ 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 +1074,18 @@ 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 +1100,16 @@ 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 +1121,8 @@ 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 +1131,13 @@ 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);
 
        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 +1166,13 @@ 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 +1210,7 @@ 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 +1250,10 @@ 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 +1278,11 @@ 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;
@@ -2739,7 +2734,8 @@ struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity)
                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)