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Message-Id: <1423224113-10958-57-git-send-email-luis.henriques@canonical.com>
Date: Fri, 6 Feb 2015 12:00:34 +0000
From: Luis Henriques <luis.henriques@...onical.com>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
kernel-team@...ts.ubuntu.com
Cc: Joe Thornber <ejt@...hat.com>, Mike Snitzer <snitzer@...hat.com>,
Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 056/135] dm cache: fix problematic dual use of a single migration count variable
3.16.7-ckt6 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Joe Thornber <ejt@...hat.com>
commit a59db67656021fa212e9b95a583f13c34eb67cd9 upstream.
Introduce a new variable to count the number of allocated migration
structures. The existing variable cache->nr_migrations became
overloaded. It was used to:
i) track of the number of migrations in flight for the purposes of
quiescing during suspend.
ii) to estimate the amount of background IO occuring.
Recent discard changes meant that REQ_DISCARD bios are processed with
a migration. Discards are not background IO so nr_migrations was not
incremented. However this could cause quiescing to complete early.
(i) is now handled with a new variable cache->nr_allocated_migrations.
cache->nr_migrations has been renamed cache->nr_io_migrations.
cleanup_migration() is now called free_io_migration(), since it
decrements that variable.
Also, remove the unused cache->next_migration variable that got replaced
with with prealloc_structs a while ago.
Signed-off-by: Joe Thornber <ejt@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
drivers/md/dm-cache-target.c | 89 +++++++++++++++++++++++++-------------------
1 file changed, 50 insertions(+), 39 deletions(-)
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index e5308b8b4043..401af32ce1e2 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -222,7 +222,13 @@ struct cache {
struct list_head need_commit_migrations;
sector_t migration_threshold;
wait_queue_head_t migration_wait;
- atomic_t nr_migrations;
+ atomic_t nr_allocated_migrations;
+
+ /*
+ * The number of in flight migrations that are performing
+ * background io. eg, promotion, writeback.
+ */
+ atomic_t nr_io_migrations;
wait_queue_head_t quiescing_wait;
atomic_t quiescing;
@@ -258,7 +264,6 @@ struct cache {
struct dm_deferred_set *all_io_ds;
mempool_t *migration_pool;
- struct dm_cache_migration *next_migration;
struct dm_cache_policy *policy;
unsigned policy_nr_args;
@@ -349,10 +354,31 @@ static void free_prison_cell(struct cache *cache, struct dm_bio_prison_cell *cel
dm_bio_prison_free_cell(cache->prison, cell);
}
+static struct dm_cache_migration *alloc_migration(struct cache *cache)
+{
+ struct dm_cache_migration *mg;
+
+ mg = mempool_alloc(cache->migration_pool, GFP_NOWAIT);
+ if (mg) {
+ mg->cache = cache;
+ atomic_inc(&mg->cache->nr_allocated_migrations);
+ }
+
+ return mg;
+}
+
+static void free_migration(struct dm_cache_migration *mg)
+{
+ if (atomic_dec_and_test(&mg->cache->nr_allocated_migrations))
+ wake_up(&mg->cache->migration_wait);
+
+ mempool_free(mg, mg->cache->migration_pool);
+}
+
static int prealloc_data_structs(struct cache *cache, struct prealloc *p)
{
if (!p->mg) {
- p->mg = mempool_alloc(cache->migration_pool, GFP_NOWAIT);
+ p->mg = alloc_migration(cache);
if (!p->mg)
return -ENOMEM;
}
@@ -381,7 +407,7 @@ static void prealloc_free_structs(struct cache *cache, struct prealloc *p)
free_prison_cell(cache, p->cell1);
if (p->mg)
- mempool_free(p->mg, cache->migration_pool);
+ free_migration(p->mg);
}
static struct dm_cache_migration *prealloc_get_migration(struct prealloc *p)
@@ -795,24 +821,14 @@ static void remap_to_origin_then_cache(struct cache *cache, struct bio *bio,
* Migration covers moving data from the origin device to the cache, or
* vice versa.
*--------------------------------------------------------------*/
-static void free_migration(struct dm_cache_migration *mg)
-{
- mempool_free(mg, mg->cache->migration_pool);
-}
-
-static void inc_nr_migrations(struct cache *cache)
+static void inc_io_migrations(struct cache *cache)
{
- atomic_inc(&cache->nr_migrations);
+ atomic_inc(&cache->nr_io_migrations);
}
-static void dec_nr_migrations(struct cache *cache)
+static void dec_io_migrations(struct cache *cache)
{
- atomic_dec(&cache->nr_migrations);
-
- /*
- * Wake the worker in case we're suspending the target.
- */
- wake_up(&cache->migration_wait);
+ atomic_dec(&cache->nr_io_migrations);
}
static void __cell_defer(struct cache *cache, struct dm_bio_prison_cell *cell,
@@ -835,11 +851,10 @@ static void cell_defer(struct cache *cache, struct dm_bio_prison_cell *cell,
wake_worker(cache);
}
-static void cleanup_migration(struct dm_cache_migration *mg)
+static void free_io_migration(struct dm_cache_migration *mg)
{
- struct cache *cache = mg->cache;
+ dec_io_migrations(mg->cache);
free_migration(mg);
- dec_nr_migrations(cache);
}
static void migration_failure(struct dm_cache_migration *mg)
@@ -864,7 +879,7 @@ static void migration_failure(struct dm_cache_migration *mg)
cell_defer(cache, mg->new_ocell, true);
}
- cleanup_migration(mg);
+ free_io_migration(mg);
}
static void migration_success_pre_commit(struct dm_cache_migration *mg)
@@ -875,7 +890,7 @@ static void migration_success_pre_commit(struct dm_cache_migration *mg)
if (mg->writeback) {
clear_dirty(cache, mg->old_oblock, mg->cblock);
cell_defer(cache, mg->old_ocell, false);
- cleanup_migration(mg);
+ free_io_migration(mg);
return;
} else if (mg->demote) {
@@ -885,14 +900,14 @@ static void migration_success_pre_commit(struct dm_cache_migration *mg)
mg->old_oblock);
if (mg->promote)
cell_defer(cache, mg->new_ocell, true);
- cleanup_migration(mg);
+ free_io_migration(mg);
return;
}
} else {
if (dm_cache_insert_mapping(cache->cmd, mg->cblock, mg->new_oblock)) {
DMWARN_LIMIT("promotion failed; couldn't update on disk metadata");
policy_remove_mapping(cache->policy, mg->new_oblock);
- cleanup_migration(mg);
+ free_io_migration(mg);
return;
}
}
@@ -925,7 +940,7 @@ static void migration_success_post_commit(struct dm_cache_migration *mg)
} else {
if (mg->invalidate)
policy_remove_mapping(cache->policy, mg->old_oblock);
- cleanup_migration(mg);
+ free_io_migration(mg);
}
} else {
@@ -940,7 +955,7 @@ static void migration_success_post_commit(struct dm_cache_migration *mg)
bio_endio(mg->new_ocell->holder, 0);
cell_defer(cache, mg->new_ocell, false);
}
- cleanup_migration(mg);
+ free_io_migration(mg);
}
}
@@ -1152,7 +1167,7 @@ static void promote(struct cache *cache, struct prealloc *structs,
mg->new_ocell = cell;
mg->start_jiffies = jiffies;
- inc_nr_migrations(cache);
+ inc_io_migrations(cache);
quiesce_migration(mg);
}
@@ -1175,7 +1190,7 @@ static void writeback(struct cache *cache, struct prealloc *structs,
mg->new_ocell = NULL;
mg->start_jiffies = jiffies;
- inc_nr_migrations(cache);
+ inc_io_migrations(cache);
quiesce_migration(mg);
}
@@ -1201,7 +1216,7 @@ static void demote_then_promote(struct cache *cache, struct prealloc *structs,
mg->new_ocell = new_ocell;
mg->start_jiffies = jiffies;
- inc_nr_migrations(cache);
+ inc_io_migrations(cache);
quiesce_migration(mg);
}
@@ -1228,7 +1243,7 @@ static void invalidate(struct cache *cache, struct prealloc *structs,
mg->new_ocell = NULL;
mg->start_jiffies = jiffies;
- inc_nr_migrations(cache);
+ inc_io_migrations(cache);
quiesce_migration(mg);
}
@@ -1289,7 +1304,7 @@ static void process_discard_bio(struct cache *cache, struct bio *bio)
static bool spare_migration_bandwidth(struct cache *cache)
{
- sector_t current_volume = (atomic_read(&cache->nr_migrations) + 1) *
+ sector_t current_volume = (atomic_read(&cache->nr_io_migrations) + 1) *
cache->sectors_per_block;
return current_volume < cache->migration_threshold;
}
@@ -1644,7 +1659,7 @@ static void stop_quiescing(struct cache *cache)
static void wait_for_migrations(struct cache *cache)
{
- wait_event(cache->migration_wait, !atomic_read(&cache->nr_migrations));
+ wait_event(cache->migration_wait, !atomic_read(&cache->nr_allocated_migrations));
}
static void stop_worker(struct cache *cache)
@@ -1755,9 +1770,6 @@ static void destroy(struct cache *cache)
{
unsigned i;
- if (cache->next_migration)
- mempool_free(cache->next_migration, cache->migration_pool);
-
if (cache->migration_pool)
mempool_destroy(cache->migration_pool);
@@ -2265,7 +2277,8 @@ static int cache_create(struct cache_args *ca, struct cache **result)
INIT_LIST_HEAD(&cache->quiesced_migrations);
INIT_LIST_HEAD(&cache->completed_migrations);
INIT_LIST_HEAD(&cache->need_commit_migrations);
- atomic_set(&cache->nr_migrations, 0);
+ atomic_set(&cache->nr_allocated_migrations, 0);
+ atomic_set(&cache->nr_io_migrations, 0);
init_waitqueue_head(&cache->migration_wait);
init_waitqueue_head(&cache->quiescing_wait);
@@ -2324,8 +2337,6 @@ static int cache_create(struct cache_args *ca, struct cache **result)
goto bad;
}
- cache->next_migration = NULL;
-
cache->need_tick_bio = true;
cache->sized = false;
cache->invalidate = false;
--
2.1.4
--
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