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dm cache: fix problematic dual use of a single migration count variable 

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@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
hifive-unleashed-5.1
Joe Thornber 2015-01-23 10:16:16 +00:00 committed by Mike Snitzer
parent 9b1cc9f251
commit a59db67656
1 changed files with 50 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

89
drivers/md/dm-cache-target.c
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@ -221,7 +221,13 @@ 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;
@ -350,10 +355,31 @@ 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;
}
@ -382,7 +408,7 @@ 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)
@ -854,24 +880,14 @@ 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)
static void inc_io_migrations(struct cache *cache)
{
mempool_free(mg, mg->cache->migration_pool);
atomic_inc(&cache->nr_io_migrations);
}
static void inc_nr_migrations(struct cache *cache)
static void dec_io_migrations(struct cache *cache)
{
atomic_inc(&cache->nr_migrations);
}
static void dec_nr_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,
@ -894,11 +910,10 @@ 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)
@ -923,7 +938,7 @@ 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)
@ -934,7 +949,7 @@ 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) {
@ -944,14 +959,14 @@ 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;
}
}
@ -984,7 +999,7 @@ 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 {
@ -999,7 +1014,7 @@ 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);
}
}
@ -1251,7 +1266,7 @@ 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);
}
@ -1275,7 +1290,7 @@ 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);
}
@ -1302,7 +1317,7 @@ 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);
}
@ -1330,7 +1345,7 @@ 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);
}
@ -1412,7 +1427,7 @@ static void process_discard_bio(struct cache *cache, struct prealloc *structs,
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;
}
@ -1764,7 +1779,7 @@ 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)
@ -1876,9 +1891,6 @@ 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);
@ -2424,7 +2436,8 @@ 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);
@ -2487,8 +2500,6 @@ 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;