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>

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 0789c22..5485377 100644 (file)
--- 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 b6bf17e..5c9186b 100644 (file)
--- 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 {