dm cache: improve efficiency of quiescing flag management

Make the quiescing flag an atomic_t and stop protecting it with a spin
lock.

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

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 25d3253e72d09b3c2263d4dfa4d68355b7ebbce1..50afdf72285beb61ab4609083711bfbc1f5dfdef 100644 (file)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -149,6 +149,7 @@ struct cache {
        atomic_t nr_migrations;
 
        wait_queue_head_t quiescing_wait;
+       atomic_t quiescing;
        atomic_t quiescing_ack;
 
        /*
@@ -189,7 +190,6 @@ struct cache {
 
        bool need_tick_bio:1;
        bool sized:1;
-       bool quiescing:1;
        bool commit_requested:1;
        bool loaded_mappings:1;
        bool loaded_discards:1;
@@ -1353,14 +1353,7 @@ static void writeback_some_dirty_blocks(struct cache *cache)
  *--------------------------------------------------------------*/
 static bool is_quiescing(struct cache *cache)
 {
-       int r;
-       unsigned long flags;
-
-       spin_lock_irqsave(&cache->lock, flags);
-       r = cache->quiescing;
-       spin_unlock_irqrestore(&cache->lock, flags);
-
-       return r;
+       return atomic_read(&cache->quiescing);
 }
 
 static void ack_quiescing(struct cache *cache)
@@ -1378,23 +1371,13 @@ static void wait_for_quiescing_ack(struct cache *cache)
 
 static void start_quiescing(struct cache *cache)
 {
-       unsigned long flags;
-
-       spin_lock_irqsave(&cache->lock, flags);
-       cache->quiescing = true;
-       spin_unlock_irqrestore(&cache->lock, flags);
-
+       atomic_inc(&cache->quiescing);
        wait_for_quiescing_ack(cache);
 }
 
 static void stop_quiescing(struct cache *cache)
 {
-       unsigned long flags;
-
-       spin_lock_irqsave(&cache->lock, flags);
-       cache->quiescing = false;
-       spin_unlock_irqrestore(&cache->lock, flags);
-
+       atomic_set(&cache->quiescing, 0);
        atomic_set(&cache->quiescing_ack, 0);
 }
 
@@ -2030,6 +2013,7 @@ static int cache_create(struct cache_args *ca, struct cache **result)
        init_waitqueue_head(&cache->migration_wait);
 
        init_waitqueue_head(&cache->quiescing_wait);
+       atomic_set(&cache->quiescing, 0);
        atomic_set(&cache->quiescing_ack, 0);
 
        r = -ENOMEM;
@@ -2091,7 +2075,6 @@ static int cache_create(struct cache_args *ca, struct cache **result)
 
        cache->need_tick_bio = true;
        cache->sized = false;
-       cache->quiescing = false;
        cache->commit_requested = false;
        cache->loaded_mappings = false;
        cache->loaded_discards = false;