dm cache: age and write back cache entries even without active IO

The policy tick() method is normally called from interrupt context.
Both the mq and smq policies do some bottom half work for the tick
method in their map functions.  However if no IO is going through the
cache, then that bottom half work doesn't occur.  With these policies
this means recently hit entries do not age and do not get written
back as early as we'd like.

Fix this by introducing a new 'can_block' parameter to the tick()
method.  When this is set the bottom half work occurs immediately.
'can_block' is set when the tick method is called every second by the
core target (not in interrupt context).

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

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/md/dm-cache-policy-smq.c b/drivers/md/dm-cache-policy-smq.c
index 55a657f78f00..66feb307e697 100644
--- a/drivers/md/dm-cache-policy-smq.c
+++ b/drivers/md/dm-cache-policy-smq.c
@@ -1581,7 +1581,7 @@ static dm_cblock_t smq_residency(struct dm_cache_policy *p)
 	return r;
 }
 
-static void smq_tick(struct dm_cache_policy *p)
+static void smq_tick(struct dm_cache_policy *p, bool can_block)
 {
 	struct smq_policy *mq = to_smq_policy(p);
 	unsigned long flags;
@@ -1589,6 +1589,12 @@ static void smq_tick(struct dm_cache_policy *p)
 	spin_lock_irqsave(&mq->tick_lock, flags);
 	mq->tick_protected++;
 	spin_unlock_irqrestore(&mq->tick_lock, flags);
+
+	if (can_block) {
+		mutex_lock(&mq->lock);
+		copy_tick(mq);
+		mutex_unlock(&mq->lock);
+	}
 }
 
 /* Init the policy plugin interface function pointers. */