dm: eliminate some holes data structures

Eliminate a 4-byte hole in 'struct dm_io_memory' by moving 'offset' above the
'ptr' to which it applies (size reduced from 24 to 16 bytes).  And by
association, 1-4 byte hole is eliminated in 'struct dm_io_request' (size
reduced from 56 to 48 bytes).

Eliminate all 6 4-byte holes and 1 cache-line in 'struct dm_snapshot' (size
reduced from 392 to 368 bytes).

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

2 files changed, 15 insertions, 15 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 0789c22ff0d4..54853773510c 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -83,10 +83,10 @@ struct dm_snapshot {
         /* Whether or not owning mapped_device is suspended */
         int suspended;
 
-        mempool_t *pending_pool;
-
         atomic_t pending_exceptions_count;
 
+        mempool_t *pending_pool;
+
         struct dm_exception_table pending;
         struct dm_exception_table complete;
 
@@ -96,6 +96,11 @@ struct dm_snapshot {
          */
         spinlock_t pe_lock;
 
+        /* Chunks with outstanding reads */
+        spinlock_t tracked_chunk_lock;
+        mempool_t *tracked_chunk_pool;
+        struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
+
         /* The on disk metadata handler */
         struct dm_exception_store *store;
 
@@ -105,10 +110,12 @@ struct dm_snapshot {
         struct bio_list queued_bios;
         struct work_struct queued_bios_work;
 
-        /* Chunks with outstanding reads */
-        mempool_t *tracked_chunk_pool;
-        spinlock_t tracked_chunk_lock;
-        struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
+        /* Wait for events based on state_bits */
+        unsigned long state_bits;
+
+        /* Range of chunks currently being merged. */
+        chunk_t first_merging_chunk;
+        int num_merging_chunks;
 
         /*
          * The merge operation failed if this flag is set.
@@ -125,13 +132,6 @@ struct dm_snapshot {
          */
         int merge_failed;
 
-        /* Wait for events based on state_bits */
-        unsigned long state_bits;
-
-        /* Range of chunks currently being merged. */
-        chunk_t first_merging_chunk;
-        int num_merging_chunks;
-
         /*
          * Incoming bios that overlap with chunks being merged must wait
          * for them to be committed.
diff --git a/include/linux/dm-io.h b/include/linux/dm-io.h
index b6bf17ee2f61..5c9186b93fff 100644
--- a/include/linux/dm-io.h
+++ b/include/linux/dm-io.h
@@ -37,14 +37,14 @@ enum dm_io_mem_type {
 struct dm_io_memory {
         enum dm_io_mem_type type;
 
+        unsigned offset;
+
         union {
                 struct page_list *pl;
                 struct bio_vec *bvec;
                 void *vma;
                 void *addr;
         } ptr;
-
-        unsigned offset;
 };
 
 struct dm_io_notify {