[PATCH -next 6/8] md/md-bitmap: support to unplug bitmap asynchrously

[Yu Kuai]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

If bitmap is enabled, bitmap must update before submiting write io, this
is why unplug callback must move these io to 'conf->pending_io_list' if
'current->bio_list' is not empty, which will suffer performance
degeration.

This patch add a new helper md_bitmap_unplug_async() to submit bitmap io
in a kworker, so that submit bitmap io in raid10_unplug() doesn't require
that 'current->bio_list' is empty.

This patch prepare to limit the number of plugged bio.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 drivers/md/md-bitmap.c | 59 +++++++++++++++++++++++++++++++++++++++---
 drivers/md/md-bitmap.h |  3 +++
 drivers/md/raid1.c     |  3 ++-
 drivers/md/raid10.c    |  2 +-
 4 files changed, 62 insertions(+), 5 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 4bd980b272ef..da8ad2e95e88 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1000,10 +1000,18 @@ static int md_bitmap_file_test_bit(struct bitmap *bitmap, sector_t block)
 	return set;
 }
 
-/* this gets called when the md device is ready to unplug its underlying
+struct bitmap_unplug_work {
+	struct work_struct work;
+	struct bitmap *bitmap;
+	struct completion *done;
+};
+
+/*
+ * This gets called when the md device is ready to unplug its underlying
  * (slave) device queues -- before we let any writes go down, we need to
- * sync the dirty pages of the bitmap file to disk */
-void md_bitmap_unplug(struct bitmap *bitmap)
+ * sync the dirty pages of the bitmap file to disk.
+ */
+static void md_do_bitmap_unplug(struct bitmap *bitmap)
 {
 	unsigned long i;
 	int dirty, need_write;
@@ -1035,9 +1043,45 @@ void md_bitmap_unplug(struct bitmap *bitmap)
 
 	if (test_bit(BITMAP_WRITE_ERROR, &bitmap->flags))
 		md_bitmap_file_kick(bitmap);
+
+}
+static void md_bitmap_unplug_fn(struct work_struct *work)
+{
+	struct bitmap_unplug_work *unplug_work =
+		container_of(work, struct bitmap_unplug_work, work);
+
+	md_do_bitmap_unplug(unplug_work->bitmap);
+	complete(unplug_work->done);
+}
+
+static void __md_bitmap_unplug(struct bitmap *bitmap, bool async)
+{
+	DECLARE_COMPLETION_ONSTACK(done);
+	struct bitmap_unplug_work unplug_work;
+
+	if (!async)
+		return md_do_bitmap_unplug(bitmap);
+
+	INIT_WORK(&unplug_work.work, md_bitmap_unplug_fn);
+	unplug_work.bitmap = bitmap;
+	unplug_work.done = &done;
+
+	queue_work(bitmap->unplug_wq, &unplug_work.work);
+	wait_for_completion(&done);
+}
+
+void md_bitmap_unplug(struct bitmap *bitmap)
+{
+	return __md_bitmap_unplug(bitmap, false);
 }
 EXPORT_SYMBOL(md_bitmap_unplug);
 
+void md_bitmap_unplug_async(struct bitmap *bitmap)
+{
+	return __md_bitmap_unplug(bitmap, true);
+}
+EXPORT_SYMBOL(md_bitmap_unplug_async);
+
 static void md_bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset, int needed);
 /* * bitmap_init_from_disk -- called at bitmap_create time to initialize
  * the in-memory bitmap from the on-disk bitmap -- also, sets up the
@@ -1753,6 +1797,9 @@ void md_bitmap_free(struct bitmap *bitmap)
 	if (!bitmap) /* there was no bitmap */
 		return;
 
+	if (bitmap->unplug_wq)
+		destroy_workqueue(bitmap->unplug_wq);
+
 	if (bitmap->sysfs_can_clear)
 		sysfs_put(bitmap->sysfs_can_clear);
 
@@ -1843,6 +1890,12 @@ struct bitmap *md_bitmap_create(struct mddev *mddev, int slot)
 	if (!bitmap)
 		return ERR_PTR(-ENOMEM);
 
+	bitmap->unplug_wq = create_workqueue("md_bitmap");
+	if (!bitmap->unplug_wq) {
+		err  = -ENOMEM;
+		goto error;
+	}
+
 	spin_lock_init(&bitmap->counts.lock);
 	atomic_set(&bitmap->pending_writes, 0);
 	init_waitqueue_head(&bitmap->write_wait);
diff --git a/drivers/md/md-bitmap.h b/drivers/md/md-bitmap.h
index 3a4750952b3a..55531669db24 100644
--- a/drivers/md/md-bitmap.h
+++ b/drivers/md/md-bitmap.h
@@ -231,6 +231,8 @@ struct bitmap {
 
 	struct kernfs_node *sysfs_can_clear;
 	int cluster_slot;		/* Slot offset for clustered env */
+
+	struct workqueue_struct *unplug_wq;
 };
 
 /* the bitmap API */
@@ -264,6 +266,7 @@ void md_bitmap_sync_with_cluster(struct mddev *mddev,
 				 sector_t new_lo, sector_t new_hi);
 
 void md_bitmap_unplug(struct bitmap *bitmap);
+void md_bitmap_unplug_async(struct bitmap *bitmap);
 void md_bitmap_daemon_work(struct mddev *mddev);
 
 int md_bitmap_resize(struct bitmap *bitmap, sector_t blocks,
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index c068ed3e6c96..7389e599f34e 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -792,7 +792,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
 static void flush_bio_list(struct r1conf *conf, struct bio *bio)
 {
 	/* flush any pending bitmap writes to disk before proceeding w/ I/O */
-	md_bitmap_unplug(conf->mddev->bitmap);
 	wake_up(&conf->wait_barrier);
 
 	while (bio) { /* submit pending writes */
@@ -829,6 +828,7 @@ static void flush_pending_writes(struct r1conf *conf)
 		 */
 		__set_current_state(TASK_RUNNING);
 		blk_start_plug(&plug);
+		md_bitmap_unplug(conf->mddev->bitmap);
 		flush_bio_list(conf, bio);
 		blk_finish_plug(&plug);
 	} else
@@ -1176,6 +1176,7 @@ static void raid1_unplug(struct blk_plug_cb *cb, bool from_schedule)
 
 	/* we aren't scheduling, so we can do the write-out directly. */
 	bio = bio_list_get(&plug->pending);
+	md_bitmap_unplug_async(conf->mddev->bitmap);
 	flush_bio_list(conf, bio);
 	kfree(plug);
 }
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index fd625026c97b..9f307ff5d4f6 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1113,7 +1113,7 @@ static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)
 
 	/* we aren't scheduling, so we can do the write-out directly. */
 	bio = bio_list_get(&plug->pending);
-	md_bitmap_unplug(mddev->bitmap);
+	md_bitmap_unplug_async(mddev->bitmap);
 	wake_up(&conf->wait_barrier);
 
 	while (bio) { /* submit pending writes */
-- 
2.39.2