dm: improve performance by moving dm_io structure to per-bio-data

Eliminates need for a separate mempool to allocate 'struct dm_io'
objects from.  As such, it saves an extra mempool allocation for each
original bio that DM core is issued.

This complicates the per-bio-data accessor functions by needing to
conditonally add extra padding to get to a target's per-bio-data.  But
in the end this provides a decent performance improvement for all
bio-based DM devices.

On an NVMe-loop based testbed to a ramdisk (~3100 MB/s): bio-based
DM linear performance improved by 2% (went from 2665 to 2777 MB/s).

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 3 insertions, 29 deletions

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 5a68b366e664..0e518d2ee280 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -314,35 +314,9 @@ struct dm_target_callbacks {
         int (*congested_fn) (struct dm_target_callbacks *, int);
 };
 
-/*
- * For bio-based dm.
- * One of these is allocated for each bio.
- * This structure shouldn't be touched directly by target drivers.
- * It is here so that we can inline dm_per_bio_data and
- * dm_bio_from_per_bio_data
- */
-struct dm_target_io {
-        struct dm_io *io;
-        struct dm_target *ti;
-        unsigned target_bio_nr;
-        unsigned *len_ptr;
-        struct bio clone;
-};
-
-static inline void *dm_per_bio_data(struct bio *bio, size_t data_size)
-{
-        return (char *)bio - offsetof(struct dm_target_io, clone) - data_size;
-}
-
-static inline struct bio *dm_bio_from_per_bio_data(void *data, size_t data_size)
-{
-        return (struct bio *)((char *)data + data_size + offsetof(struct dm_target_io, clone));
-}
-
-static inline unsigned dm_bio_get_target_bio_nr(const struct bio *bio)
-{
-        return container_of(bio, struct dm_target_io, clone)->target_bio_nr;
-}
+void *dm_per_bio_data(struct bio *bio, size_t data_size);
+struct bio *dm_bio_from_per_bio_data(void *data, size_t data_size);
+unsigned dm_bio_get_target_bio_nr(const struct bio *bio);
 
 int dm_register_target(struct target_type *t);
 void dm_unregister_target(struct target_type *t);