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>
diff --git a/drivers/md/dm-cache-policy-mq.c b/drivers/md/dm-cache-policy-mq.c
index 084eec6..838665b 100644
--- a/drivers/md/dm-cache-policy-mq.c
+++ b/drivers/md/dm-cache-policy-mq.c
@@ -1283,7 +1283,7 @@
return r;
}
-static void mq_tick(struct dm_cache_policy *p)
+static void mq_tick(struct dm_cache_policy *p, bool can_block)
{
struct mq_policy *mq = to_mq_policy(p);
unsigned long flags;
@@ -1291,6 +1291,12 @@
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);
+ }
}
static int mq_set_config_value(struct dm_cache_policy *p,