dm thin: add mappings to end of prepared_* lists

Mappings could be processed in descending logical block order,
particularly if buffered IO is used.  This could adversely affect the
latency of IO processing.  Fix this by adding mappings to the end of the
'prepared_mappings' and 'prepared_discards' lists.

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

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index b721d7a636292a837b7787afebb2a1a480538002..850e7cddb7afed7906f7014af505fc08ac7a1820 100644 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -535,7 +535,7 @@ static void __maybe_add_mapping(struct dm_thin_new_mapping *m)
        struct pool *pool = m->tc->pool;
 
        if (m->quiesced && m->prepared) {
-               list_add(&m->list, &pool->prepared_mappings);
+               list_add_tail(&m->list, &pool->prepared_mappings);
                wake_worker(pool);
        }
 }
@@ -1062,7 +1062,7 @@ static void process_discard(struct thin_c *tc, struct bio *bio)
 
                        if (!dm_deferred_set_add_work(pool->all_io_ds, &m->list)) {
                                spin_lock_irqsave(&pool->lock, flags);
-                               list_add(&m->list, &pool->prepared_discards);
+                               list_add_tail(&m->list, &pool->prepared_discards);
                                spin_unlock_irqrestore(&pool->lock, flags);
                                wake_worker(pool);
                        }
@@ -2923,7 +2923,7 @@ static int thin_endio(struct dm_target *ti, struct bio *bio, int err)
                if (!list_empty(&work)) {
                        spin_lock_irqsave(&pool->lock, flags);
                        list_for_each_entry_safe(m, tmp, &work, list)
-                               list_add(&m->list, &pool->prepared_discards);
+                               list_add_tail(&m->list, &pool->prepared_discards);
                        spin_unlock_irqrestore(&pool->lock, flags);
                        wake_worker(pool);
                }