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authorJoe Thornber <ejt@redhat.com>2014-10-22 14:30:58 +0100
committerMike Snitzer <snitzer@redhat.com>2014-11-10 15:25:29 -0500
commitb155aa0e5a81ea1f05ff7aced0ec8e34c980c19e (patch)
tree56f73848b2e70f8a9eb4d97d51b742fc93c3ad0f /drivers/md
parent41abc4e1af369bb5438eaee398e3beee690cc8ca (diff)
dm cache policy mq: tweak algorithm that decides when to promote a block
Rather than maintaining a separate promote_threshold variable that we periodically update we now use the hit count of the oldest clean block. Also add a fudge factor to discourage demoting dirty blocks. With some tests this has a sizeable difference, because the old code was too eager to demote blocks. For example, device-mapper-test-suite's git_extract_cache_quick test goes from taking 190 seconds, to 142 (linear on spindle takes 250). Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/dm-cache-policy-mq.c75
1 files changed, 50 insertions, 25 deletions
diff --git a/drivers/md/dm-cache-policy-mq.c b/drivers/md/dm-cache-policy-mq.c
index 0e385e40909e..334d098d720d 100644
--- a/drivers/md/dm-cache-policy-mq.c
+++ b/drivers/md/dm-cache-policy-mq.c
@@ -181,24 +181,30 @@ static void queue_shift_down(struct queue *q)
* Gives us the oldest entry of the lowest popoulated level. If the first
* level is emptied then we shift down one level.
*/
-static struct list_head *queue_pop(struct queue *q)
+static struct list_head *queue_peek(struct queue *q)
{
unsigned level;
- struct list_head *r;
for (level = 0; level < NR_QUEUE_LEVELS; level++)
- if (!list_empty(q->qs + level)) {
- r = q->qs[level].next;
- list_del(r);
+ if (!list_empty(q->qs + level))
+ return q->qs[level].next;
- /* have we just emptied the bottom level? */
- if (level == 0 && list_empty(q->qs))
- queue_shift_down(q);
+ return NULL;
+}
- return r;
- }
+static struct list_head *queue_pop(struct queue *q)
+{
+ struct list_head *r = queue_peek(q);
- return NULL;
+ if (r) {
+ list_del(r);
+
+ /* have we just emptied the bottom level? */
+ if (list_empty(q->qs))
+ queue_shift_down(q);
+ }
+
+ return r;
}
static struct list_head *list_pop(struct list_head *lh)
@@ -383,13 +389,6 @@ struct mq_policy {
unsigned generation;
unsigned generation_period; /* in lookups (will probably change) */
- /*
- * Entries in the pre_cache whose hit count passes the promotion
- * threshold move to the cache proper. Working out the correct
- * value for the promotion_threshold is crucial to this policy.
- */
- unsigned promote_threshold;
-
unsigned discard_promote_adjustment;
unsigned read_promote_adjustment;
unsigned write_promote_adjustment;
@@ -406,6 +405,7 @@ struct mq_policy {
#define DEFAULT_DISCARD_PROMOTE_ADJUSTMENT 1
#define DEFAULT_READ_PROMOTE_ADJUSTMENT 4
#define DEFAULT_WRITE_PROMOTE_ADJUSTMENT 8
+#define DISCOURAGE_DEMOTING_DIRTY_THRESHOLD 128
/*----------------------------------------------------------------*/
@@ -518,6 +518,12 @@ static struct entry *pop(struct mq_policy *mq, struct queue *q)
return e;
}
+static struct entry *peek(struct queue *q)
+{
+ struct list_head *h = queue_peek(q);
+ return h ? container_of(h, struct entry, list) : NULL;
+}
+
/*
* Has this entry already been updated?
*/
@@ -570,10 +576,6 @@ static void check_generation(struct mq_policy *mq)
break;
}
}
-
- mq->promote_threshold = nr ? total / nr : 1;
- if (mq->promote_threshold * nr < total)
- mq->promote_threshold++;
}
}
@@ -641,6 +643,30 @@ static int demote_cblock(struct mq_policy *mq, dm_oblock_t *oblock)
}
/*
+ * Entries in the pre_cache whose hit count passes the promotion
+ * threshold move to the cache proper. Working out the correct
+ * value for the promotion_threshold is crucial to this policy.
+ */
+static unsigned promote_threshold(struct mq_policy *mq)
+{
+ struct entry *e;
+
+ if (any_free_cblocks(mq))
+ return 0;
+
+ e = peek(&mq->cache_clean);
+ if (e)
+ return e->hit_count;
+
+ e = peek(&mq->cache_dirty);
+ if (e)
+ return e->hit_count + DISCOURAGE_DEMOTING_DIRTY_THRESHOLD;
+
+ /* This should never happen */
+ return 0;
+}
+
+/*
* We modify the basic promotion_threshold depending on the specific io.
*
* If the origin block has been discarded then there's no cost to copy it
@@ -653,7 +679,7 @@ static unsigned adjusted_promote_threshold(struct mq_policy *mq,
bool discarded_oblock, int data_dir)
{
if (data_dir == READ)
- return mq->promote_threshold + mq->read_promote_adjustment;
+ return promote_threshold(mq) + mq->read_promote_adjustment;
if (discarded_oblock && (any_free_cblocks(mq) || any_clean_cblocks(mq))) {
/*
@@ -663,7 +689,7 @@ static unsigned adjusted_promote_threshold(struct mq_policy *mq,
return mq->discard_promote_adjustment;
}
- return mq->promote_threshold + mq->write_promote_adjustment;
+ return promote_threshold(mq) + mq->write_promote_adjustment;
}
static bool should_promote(struct mq_policy *mq, struct entry *e,
@@ -1230,7 +1256,6 @@ static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
mq->tick = 0;
mq->hit_count = 0;
mq->generation = 0;
- mq->promote_threshold = 0;
mq->discard_promote_adjustment = DEFAULT_DISCARD_PROMOTE_ADJUSTMENT;
mq->read_promote_adjustment = DEFAULT_READ_PROMOTE_ADJUSTMENT;
mq->write_promote_adjustment = DEFAULT_WRITE_PROMOTE_ADJUSTMENT;

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