dm cache: eliminate holes in cache structure

Reorder members in the cache structure to eliminate 6 out of 7 holes
(reclaiming 24 bytes).  Also, the 'worker' and 'waker' members no longer
straddle cachelines.

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

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 22ff650..2956976 100644 (file)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -103,6 +103,8 @@ struct cache {
        struct dm_target *ti;
        struct dm_target_callbacks callbacks;
 
+       struct dm_cache_metadata *cmd;
+
        /*
         * Metadata is written to this device.
         */
@@ -118,11 +120,6 @@ struct cache {
         */
        struct dm_dev *cache_dev;
 
-       /*
-        * Cache features such as write-through.
-        */
-       struct cache_features features;
-
        /*
         * Size of the origin device in _complete_ blocks and native sectors.
         */
@@ -140,8 +137,6 @@ struct cache {
        uint32_t sectors_per_block;
        int sectors_per_block_shift;
 
-       struct dm_cache_metadata *cmd;
-
        spinlock_t lock;
        struct bio_list deferred_bios;
        struct bio_list deferred_flush_bios;
@@ -150,8 +145,8 @@ struct cache {
        struct list_head completed_migrations;
        struct list_head need_commit_migrations;
        sector_t migration_threshold;
-       atomic_t nr_migrations;
        wait_queue_head_t migration_wait;
+       atomic_t nr_migrations;
 
        /*
         * cache_size entries, dirty if set
@@ -162,9 +157,16 @@ struct cache {
        /*
         * origin_blocks entries, discarded if set.
         */
-       uint32_t discard_block_size; /* a power of 2 times sectors per block */
        dm_dblock_t discard_nr_blocks;
        unsigned long *discard_bitset;
+       uint32_t discard_block_size; /* a power of 2 times sectors per block */
+
+       /*
+        * Rather than reconstructing the table line for the status we just
+        * save it and regurgitate.
+        */
+       unsigned nr_ctr_args;
+       const char **ctr_args;
 
        struct dm_kcopyd_client *copier;
        struct workqueue_struct *wq;
@@ -189,14 +191,12 @@ struct cache {
        bool loaded_mappings:1;
        bool loaded_discards:1;
 
-       struct cache_stats stats;
-
        /*
-        * Rather than reconstructing the table line for the status we just
-        * save it and regurgitate.
+        * Cache features such as write-through.
         */
-       unsigned nr_ctr_args;
-       const char **ctr_args;
+       struct cache_features features;
+
+       struct cache_stats stats;
 };
 
 struct per_bio_data {