dm thin: use per thin device deferred bio lists

The thin-pool previously only had a single deferred_bios list that would
collect bios for all thin devices in the pool.  Split this per-pool
deferred_bios list out to per-thin deferred_bios_list -- doing so
enables increased parallelism when processing deferred bios.  And now
that each thin device has it's own deferred_bios_list we can sort all
bios in the list using logical sector.  The requeue code in error
handling path is also cleaner as a side-effect.

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

1 files changed, 104 insertions, 61 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index af871fd48eb4..08e62aef361d 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -12,6 +12,7 @@
 #include <linux/dm-io.h>
 #include <linux/dm-kcopyd.h>
 #include <linux/list.h>
+#include <linux/rculist.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/slab.h>
@@ -178,12 +179,10 @@ struct pool {
         unsigned ref_count;
 
         spinlock_t lock;
-        struct bio_list deferred_bios;
         struct bio_list deferred_flush_bios;
         struct list_head prepared_mappings;
         struct list_head prepared_discards;
-
-        struct bio_list retry_on_resume_list;
+        struct list_head active_thins;
 
         struct dm_deferred_set *shared_read_ds;
         struct dm_deferred_set *all_io_ds;
@@ -220,6 +219,7 @@ struct pool_c {
  * Target context for a thin.
  */
 struct thin_c {
+        struct list_head list;
         struct dm_dev *pool_dev;
         struct dm_dev *origin_dev;
         dm_thin_id dev_id;
@@ -227,6 +227,9 @@ struct thin_c {
         struct pool *pool;
         struct dm_thin_device *td;
         bool requeue_mode:1;
+        spinlock_t lock;
+        struct bio_list deferred_bio_list;
+        struct bio_list retry_on_resume_list;
 };
 
 /*----------------------------------------------------------------*/
@@ -287,9 +290,9 @@ static void cell_defer_no_holder_no_free(struct thin_c *tc,
         struct pool *pool = tc->pool;
         unsigned long flags;
 
-        spin_lock_irqsave(&pool->lock, flags);
-        dm_cell_release_no_holder(pool->prison, cell, &pool->deferred_bios);
-        spin_unlock_irqrestore(&pool->lock, flags);
+        spin_lock_irqsave(&tc->lock, flags);
+        dm_cell_release_no_holder(pool->prison, cell, &tc->deferred_bio_list);
+        spin_unlock_irqrestore(&tc->lock, flags);
 
         wake_worker(pool);
 }
@@ -378,30 +381,22 @@ static void requeue_bio_list(struct thin_c *tc, struct bio_list *master)
 
         bio_list_init(&bios);
 
-        spin_lock_irqsave(&tc->pool->lock, flags);
+        spin_lock_irqsave(&tc->lock, flags);
         bio_list_merge(&bios, master);
         bio_list_init(master);
-        spin_unlock_irqrestore(&tc->pool->lock, flags);
+        spin_unlock_irqrestore(&tc->lock, flags);
 
-        while ((bio = bio_list_pop(&bios))) {
-                struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
-
-                if (h->tc == tc)
-                        bio_endio(bio, DM_ENDIO_REQUEUE);
-                else
-                        bio_list_add(master, bio);
-        }
+        while ((bio = bio_list_pop(&bios)))
+                bio_endio(bio, DM_ENDIO_REQUEUE);
 }
 
 static void requeue_io(struct thin_c *tc)
 {
-        struct pool *pool = tc->pool;
-
-        requeue_bio_list(tc, &pool->deferred_bios);
-        requeue_bio_list(tc, &pool->retry_on_resume_list);
+        requeue_bio_list(tc, &tc->deferred_bio_list);
+        requeue_bio_list(tc, &tc->retry_on_resume_list);
 }
 
-static void error_retry_list(struct pool *pool)
+static void error_thin_retry_list(struct thin_c *tc)
 {
         struct bio *bio;
         unsigned long flags;
@@ -409,15 +404,25 @@ static void error_retry_list(struct pool *pool)
 
         bio_list_init(&bios);
 
-        spin_lock_irqsave(&pool->lock, flags);
-        bio_list_merge(&bios, &pool->retry_on_resume_list);
-        bio_list_init(&pool->retry_on_resume_list);
-        spin_unlock_irqrestore(&pool->lock, flags);
+        spin_lock_irqsave(&tc->lock, flags);
+        bio_list_merge(&bios, &tc->retry_on_resume_list);
+        bio_list_init(&tc->retry_on_resume_list);
+        spin_unlock_irqrestore(&tc->lock, flags);
 
         while ((bio = bio_list_pop(&bios)))
                 bio_io_error(bio);
 }
 
+static void error_retry_list(struct pool *pool)
+{
+        struct thin_c *tc;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(tc, &pool->active_thins, list)
+                error_thin_retry_list(tc);
+        rcu_read_unlock();
+}
+
 /*
  * This section of code contains the logic for processing a thin device's IO.
  * Much of the code depends on pool object resources (lists, workqueues, etc)
@@ -608,9 +613,9 @@ static void cell_defer(struct thin_c *tc, struct dm_bio_prison_cell *cell)
         struct pool *pool = tc->pool;
         unsigned long flags;
 
-        spin_lock_irqsave(&pool->lock, flags);
-        cell_release(pool, cell, &pool->deferred_bios);
-        spin_unlock_irqrestore(&tc->pool->lock, flags);
+        spin_lock_irqsave(&tc->lock, flags);
+        cell_release(pool, cell, &tc->deferred_bio_list);
+        spin_unlock_irqrestore(&tc->lock, flags);
 
         wake_worker(pool);
 }
@@ -623,9 +628,9 @@ static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *c
         struct pool *pool = tc->pool;
         unsigned long flags;
 
-        spin_lock_irqsave(&pool->lock, flags);
-        cell_release_no_holder(pool, cell, &pool->deferred_bios);
-        spin_unlock_irqrestore(&pool->lock, flags);
+        spin_lock_irqsave(&tc->lock, flags);
+        cell_release_no_holder(pool, cell, &tc->deferred_bio_list);
+        spin_unlock_irqrestore(&tc->lock, flags);
 
         wake_worker(pool);
 }
@@ -1001,12 +1006,11 @@ static void retry_on_resume(struct bio *bio)
 {
         struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
         struct thin_c *tc = h->tc;
-        struct pool *pool = tc->pool;
         unsigned long flags;
 
-        spin_lock_irqsave(&pool->lock, flags);
-        bio_list_add(&pool->retry_on_resume_list, bio);
-        spin_unlock_irqrestore(&pool->lock, flags);
+        spin_lock_irqsave(&tc->lock, flags);
+        bio_list_add(&tc->retry_on_resume_list, bio);
+        spin_unlock_irqrestore(&tc->lock, flags);
 }
 
 static bool should_error_unserviceable_bio(struct pool *pool)
@@ -1363,38 +1367,36 @@ static int need_commit_due_to_time(struct pool *pool)
                jiffies > pool->last_commit_jiffies + COMMIT_PERIOD;
 }
 
-static void process_deferred_bios(struct pool *pool)
+static void process_thin_deferred_bios(struct thin_c *tc)
 {
+        struct pool *pool = tc->pool;
         unsigned long flags;
         struct bio *bio;
         struct bio_list bios;
 
+        if (tc->requeue_mode) {
+                requeue_bio_list(tc, &tc->deferred_bio_list);
+                return;
+        }
+
         bio_list_init(&bios);
 
-        spin_lock_irqsave(&pool->lock, flags);
-        bio_list_merge(&bios, &pool->deferred_bios);
-        bio_list_init(&pool->deferred_bios);
-        spin_unlock_irqrestore(&pool->lock, flags);
+        spin_lock_irqsave(&tc->lock, flags);
+        bio_list_merge(&bios, &tc->deferred_bio_list);
+        bio_list_init(&tc->deferred_bio_list);
+        spin_unlock_irqrestore(&tc->lock, flags);
 
         while ((bio = bio_list_pop(&bios))) {
-                struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
-                struct thin_c *tc = h->tc;
-
-                if (tc->requeue_mode) {
-                        bio_endio(bio, DM_ENDIO_REQUEUE);
-                        continue;
-                }
-
                 /*
                  * If we've got no free new_mapping structs, and processing
                  * this bio might require one, we pause until there are some
                  * prepared mappings to process.
                  */
                 if (ensure_next_mapping(pool)) {
-                        spin_lock_irqsave(&pool->lock, flags);
-                        bio_list_add(&pool->deferred_bios, bio);
-                        bio_list_merge(&pool->deferred_bios, &bios);
-                        spin_unlock_irqrestore(&pool->lock, flags);
+                        spin_lock_irqsave(&tc->lock, flags);
+                        bio_list_add(&tc->deferred_bio_list, bio);
+                        bio_list_merge(&tc->deferred_bio_list, &bios);
+                        spin_unlock_irqrestore(&tc->lock, flags);
                         break;
                 }
 
@@ -1403,6 +1405,19 @@ static void process_deferred_bios(struct pool *pool)
                 else
                         pool->process_bio(tc, bio);
         }
+}
+
+static void process_deferred_bios(struct pool *pool)
+{
+        unsigned long flags;
+        struct bio *bio;
+        struct bio_list bios;
+        struct thin_c *tc;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(tc, &pool->active_thins, list)
+                process_thin_deferred_bios(tc);
+        rcu_read_unlock();
 
         /*
          * If there are any deferred flush bios, we must commit
@@ -1634,9 +1649,9 @@ static void thin_defer_bio(struct thin_c *tc, struct bio *bio)
         unsigned long flags;
         struct pool *pool = tc->pool;
 
-        spin_lock_irqsave(&pool->lock, flags);
-        bio_list_add(&pool->deferred_bios, bio);
-        spin_unlock_irqrestore(&pool->lock, flags);
+        spin_lock_irqsave(&tc->lock, flags);
+        bio_list_add(&tc->deferred_bio_list, bio);
+        spin_unlock_irqrestore(&tc->lock, flags);
 
         wake_worker(pool);
 }
@@ -1767,10 +1782,19 @@ static int pool_is_congested(struct dm_target_callbacks *cb, int bdi_bits)
         return bdi_congested(&q->backing_dev_info, bdi_bits);
 }
 
-static void __requeue_bios(struct pool *pool)
+static void requeue_bios(struct pool *pool)
 {
-        bio_list_merge(&pool->deferred_bios, &pool->retry_on_resume_list);
-        bio_list_init(&pool->retry_on_resume_list);
+        unsigned long flags;
+        struct thin_c *tc;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(tc, &pool->active_thins, list) {
+                spin_lock_irqsave(&tc->lock, flags);
+                bio_list_merge(&tc->deferred_bio_list, &tc->retry_on_resume_list);
+                bio_list_init(&tc->retry_on_resume_list);
+                spin_unlock_irqrestore(&tc->lock, flags);
+        }
+        rcu_read_unlock();
 }
 
 /*----------------------------------------------------------------
@@ -1951,12 +1975,11 @@ static struct pool *pool_create(struct mapped_device *pool_md,
         INIT_WORK(&pool->worker, do_worker);
         INIT_DELAYED_WORK(&pool->waker, do_waker);
         spin_lock_init(&pool->lock);
-        bio_list_init(&pool->deferred_bios);
         bio_list_init(&pool->deferred_flush_bios);
         INIT_LIST_HEAD(&pool->prepared_mappings);
         INIT_LIST_HEAD(&pool->prepared_discards);
+        INIT_LIST_HEAD(&pool->active_thins);
         pool->low_water_triggered = false;
-        bio_list_init(&pool->retry_on_resume_list);
 
         pool->shared_read_ds = dm_deferred_set_create();
         if (!pool->shared_read_ds) {
@@ -2501,8 +2524,8 @@ static void pool_resume(struct dm_target *ti)
 
         spin_lock_irqsave(&pool->lock, flags);
         pool->low_water_triggered = false;
-        __requeue_bios(pool);
         spin_unlock_irqrestore(&pool->lock, flags);
+        requeue_bios(pool);
 
         do_waker(&pool->waker.work);
 }
@@ -2962,6 +2985,12 @@ static struct target_type pool_target = {
 static void thin_dtr(struct dm_target *ti)
 {
         struct thin_c *tc = ti->private;
+        unsigned long flags;
+
+        spin_lock_irqsave(&tc->pool->lock, flags);
+        list_del_rcu(&tc->list);
+        spin_unlock_irqrestore(&tc->pool->lock, flags);
+        synchronize_rcu();
 
         mutex_lock(&dm_thin_pool_table.mutex);
 
@@ -3008,6 +3037,9 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
                 r = -ENOMEM;
                 goto out_unlock;
         }
+        spin_lock_init(&tc->lock);
+        bio_list_init(&tc->deferred_bio_list);
+        bio_list_init(&tc->retry_on_resume_list);
 
         if (argc == 3) {
                 r = dm_get_device(ti, argv[2], FMODE_READ, &origin_dev);
@@ -3079,6 +3111,17 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
 
         mutex_unlock(&dm_thin_pool_table.mutex);
 
+        spin_lock(&tc->pool->lock);
+        list_add_tail_rcu(&tc->list, &tc->pool->active_thins);
+        spin_unlock(&tc->pool->lock);
+        /*
+         * This synchronize_rcu() call is needed here otherwise we risk a
+         * wake_worker() call finding no bios to process (because the newly
+         * added tc isn't yet visible).  So this reduces latency since we
+         * aren't then dependent on the periodic commit to wake_worker().
+         */
+        synchronize_rcu();
+
         return 0;
 
 bad_target_max_io_len: