md/raid5: add simple plugging infrastructure.

md/raid5 uses the plugging infrastructure provided by the block layer
and 'struct request_queue'.  However when we plug raid5 under dm there
is no request queue so we cannot use that.

So create a similar infrastructure that is much lighter weight and use
it for raid5.

Signed-off-by: NeilBrown <neilb@suse.de>

4 files changed, 93 insertions, 14 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index f8775699e15a..eec75f130708 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -386,6 +386,51 @@ void md_barrier_request(mddev_t *mddev, struct bio *bio)
 }
 EXPORT_SYMBOL(md_barrier_request);
 
+/* Support for plugging.
+ * This mirrors the plugging support in request_queue, but does not
+ * require having a whole queue
+ */
+static void plugger_work(struct work_struct *work)
+{
+        struct plug_handle *plug =
+                container_of(work, struct plug_handle, unplug_work);
+        plug->unplug_fn(plug);
+}
+static void plugger_timeout(unsigned long data)
+{
+        struct plug_handle *plug = (void *)data;
+        kblockd_schedule_work(NULL, &plug->unplug_work);
+}
+void plugger_init(struct plug_handle *plug,
+                  void (*unplug_fn)(struct plug_handle *))
+{
+        plug->unplug_flag = 0;
+        plug->unplug_fn = unplug_fn;
+        init_timer(&plug->unplug_timer);
+        plug->unplug_timer.function = plugger_timeout;
+        plug->unplug_timer.data = (unsigned long)plug;
+        INIT_WORK(&plug->unplug_work, plugger_work);
+}
+EXPORT_SYMBOL_GPL(plugger_init);
+
+void plugger_set_plug(struct plug_handle *plug)
+{
+        if (!test_and_set_bit(PLUGGED_FLAG, &plug->unplug_flag))
+                mod_timer(&plug->unplug_timer, jiffies + msecs_to_jiffies(3)+1);
+}
+EXPORT_SYMBOL_GPL(plugger_set_plug);
+
+int plugger_remove_plug(struct plug_handle *plug)
+{
+        if (test_and_clear_bit(PLUGGED_FLAG, &plug->unplug_flag)) {
+                del_timer(&plug->unplug_timer);
+                return 1;
+        } else
+                return 0;
+}
+EXPORT_SYMBOL_GPL(plugger_remove_plug);
+
+
 static inline mddev_t *mddev_get(mddev_t *mddev)
 {
         atomic_inc(&mddev->active);
diff --git a/drivers/md/md.h b/drivers/md/md.h
index c88b04745e85..5be0d6921b9d 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -29,6 +29,26 @@
 typedef struct mddev_s mddev_t;
 typedef struct mdk_rdev_s mdk_rdev_t;
 
+/* generic plugging support - like that provided with request_queue,
+ * but does not require a request_queue
+ */
+struct plug_handle {
+        void                    (*unplug_fn)(struct plug_handle *);
+        struct timer_list       unplug_timer;
+        struct work_struct      unplug_work;
+        unsigned long           unplug_flag;
+};
+#define PLUGGED_FLAG 1
+void plugger_init(struct plug_handle *plug,
+                  void (*unplug_fn)(struct plug_handle *));
+void plugger_set_plug(struct plug_handle *plug);
+int plugger_remove_plug(struct plug_handle *plug);
+static inline void plugger_flush(struct plug_handle *plug)
+{
+        del_timer_sync(&plug->unplug_timer);
+        cancel_work_sync(&plug->unplug_work);
+}
+
 /*
  * MD's 'extended' device
  */
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index ad6694f8a3a8..84bb9aec2211 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -201,11 +201,11 @@ static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
                 if (test_bit(STRIPE_HANDLE, &sh->state)) {
                         if (test_bit(STRIPE_DELAYED, &sh->state)) {
                                 list_add_tail(&sh->lru, &conf->delayed_list);
-                                blk_plug_device(conf->mddev->queue);
+                                plugger_set_plug(&conf->plug);
                         } else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
                                    sh->bm_seq - conf->seq_write > 0) {
                                 list_add_tail(&sh->lru, &conf->bitmap_list);
-                                blk_plug_device(conf->mddev->queue);
+                                plugger_set_plug(&conf->plug);
                         } else {
                                 clear_bit(STRIPE_BIT_DELAY, &sh->state);
                                 list_add_tail(&sh->lru, &conf->handle_list);
@@ -434,7 +434,7 @@ static int has_failed(raid5_conf_t *conf)
 }
 
 static void unplug_slaves(mddev_t *mddev);
-static void raid5_unplug_device(struct request_queue *q);
+static void raid5_unplug_device(raid5_conf_t *conf);
 
 static struct stripe_head *
 get_active_stripe(raid5_conf_t *conf, sector_t sector,
@@ -464,7 +464,7 @@ get_active_stripe(raid5_conf_t *conf, sector_t sector,
                                                      < (conf->max_nr_stripes *3/4)
                                                      || !conf->inactive_blocked),
                                                     conf->device_lock,
-                                                    raid5_unplug_device(conf->mddev->queue)
+                                                    raid5_unplug_device(conf)
                                         );
                                 conf->inactive_blocked = 0;
                         } else
@@ -3618,7 +3618,7 @@ static void raid5_activate_delayed(raid5_conf_t *conf)
                         list_add_tail(&sh->lru, &conf->hold_list);
                 }
         } else
-                blk_plug_device(conf->mddev->queue);
+                plugger_set_plug(&conf->plug);
 }
 
 static void activate_bit_delay(raid5_conf_t *conf)
@@ -3659,23 +3659,33 @@ static void unplug_slaves(mddev_t *mddev)
         rcu_read_unlock();
 }
 
-static void raid5_unplug_device(struct request_queue *q)
+static void raid5_unplug_device(raid5_conf_t *conf)
 {
-        mddev_t *mddev = q->queuedata;
-        raid5_conf_t *conf = mddev->private;
         unsigned long flags;
 
         spin_lock_irqsave(&conf->device_lock, flags);
 
-        if (blk_remove_plug(q)) {
+        if (plugger_remove_plug(&conf->plug)) {
                 conf->seq_flush++;
                 raid5_activate_delayed(conf);
         }
-        md_wakeup_thread(mddev->thread);
+        md_wakeup_thread(conf->mddev->thread);
 
         spin_unlock_irqrestore(&conf->device_lock, flags);
 
-        unplug_slaves(mddev);
+        unplug_slaves(conf->mddev);
+}
+
+static void raid5_unplug(struct plug_handle *plug)
+{
+        raid5_conf_t *conf = container_of(plug, raid5_conf_t, plug);
+        raid5_unplug_device(conf);
+}
+
+static void raid5_unplug_queue(struct request_queue *q)
+{
+        mddev_t *mddev = q->queuedata;
+        raid5_unplug_device(mddev->private);
 }
 
 int md_raid5_congested(mddev_t *mddev, int bits)
@@ -4085,7 +4095,7 @@ static int make_request(mddev_t *mddev, struct bio * bi)
                                  * add failed due to overlap.  Flush everything
                                  * and wait a while
                                  */
-                                raid5_unplug_device(mddev->queue);
+                                raid5_unplug_device(conf);
                                 release_stripe(sh);
                                 schedule();
                                 goto retry;
@@ -5178,6 +5188,7 @@ static int run(mddev_t *mddev)
                        mdname(mddev));
         md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
 
+        plugger_init(&conf->plug, raid5_unplug);
         if (mddev->queue) {
                 /* read-ahead size must cover two whole stripes, which
                  * is 2 * (datadisks) * chunksize where 'n' is the
@@ -5197,7 +5208,7 @@ static int run(mddev_t *mddev)
 
         mddev->queue->queue_lock = &conf->device_lock;
 
-        mddev->queue->unplug_fn = raid5_unplug_device;
+        mddev->queue->unplug_fn = raid5_unplug_queue;
 
         chunk_size = mddev->chunk_sectors << 9;
         blk_queue_io_min(mddev->queue, chunk_size);
@@ -5229,7 +5240,7 @@ static int stop(mddev_t *mddev)
         mddev->thread = NULL;
         if (mddev->queue)
                 mddev->queue->backing_dev_info.congested_fn = NULL;
-        blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
+        plugger_flush(&conf->plug); /* the unplug fn references 'conf'*/
         free_conf(conf);
         mddev->private = NULL;
         mddev->to_remove = &raid5_attrs_group;
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index d6470dec667a..6acd458f239d 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -398,6 +398,9 @@ struct raid5_private_data {
                                             * (fresh device added).
                                             * Cleared when a sync completes.
                                             */
+
+        struct plug_handle      plug;
+
         /* per cpu variables */
         struct raid5_percpu {
                 struct page     *spare_page; /* Used when checking P/Q in raid6 */