Commit 34db0cd6 authored by NeilBrown's avatar NeilBrown
Browse files

md: add proper write-congestion reporting to RAID1 and RAID10. 



RAID1 and RAID10 handle write requests by queuing them for handling by
a separate thread.  This is because when a write-intent-bitmap is
active we might need to update the bitmap first, so it is good to
queue a lot of writes, then do one big bitmap update for them all.

However writeback request devices to appear to be congested after a
while so it can make some guesstimate of throughput.  The infinite
queue defeats that (note that RAID5 has already has a finite queue so
it doesn't suffer from this problem).

So impose a limit on the number of pending write requests.  By default
it is 1024 which seems to be generally suitable.  Make it configurable
via module option just in case someone finds a regression.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 84fc4b56

drivers/md/raid1.c

+20 −0
Original line number Diff line number Diff line
@@ -45,6 +45,11 @@ 
 */

#define	NR_RAID1_BIOS 256



/* When there are this many requests queue to be written by

 * the raid1 thread, we become 'congested' to provide back-pressure

 * for writeback.

 */

static int max_queued_requests = 1024;



static void allow_barrier(struct r1conf *conf);

static void lower_barrier(struct r1conf *conf);
@@ -598,6 +603,10 @@ int md_raid1_congested(struct mddev *mddev, int bits) 
	struct r1conf *conf = mddev->private;

	int i, ret = 0;



	if ((bits & (1 << BDI_async_congested)) &&

	    conf->pending_count >= max_queued_requests)

		return 1;



	rcu_read_lock();

	for (i = 0; i < mddev->raid_disks; i++) {

		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
@@ -638,10 +647,12 @@ static void flush_pending_writes(struct r1conf *conf) 
	if (conf->pending_bio_list.head) {

		struct bio *bio;

		bio = bio_list_get(&conf->pending_bio_list);

		conf->pending_count = 0;

		spin_unlock_irq(&conf->device_lock);

		/* flush any pending bitmap writes to

		 * disk before proceeding w/ I/O */

		bitmap_unplug(conf->mddev->bitmap);

		wake_up(&conf->wait_barrier);



		while (bio) { /* submit pending writes */

			struct bio *next = bio->bi_next;
@@ -945,6 +956,11 @@ read_again: 
	/*

	 * WRITE:

	 */

	if (conf->pending_count >= max_queued_requests) {

		md_wakeup_thread(mddev->thread);

		wait_event(conf->wait_barrier,

			   conf->pending_count < max_queued_requests);

	}

	/* first select target devices under rcu_lock and

	 * inc refcount on their rdev.  Record them by setting

	 * bios[x] to bio
@@ -1108,6 +1124,7 @@ read_again: 
		atomic_inc(&r1_bio->remaining);

		spin_lock_irqsave(&conf->device_lock, flags);

		bio_list_add(&conf->pending_bio_list, mbio);

		conf->pending_count++;

		spin_unlock_irqrestore(&conf->device_lock, flags);

	}

	/* Mustn't call r1_bio_write_done before this next test,
@@ -2418,6 +2435,7 @@ static struct r1conf *setup_conf(struct mddev *mddev) 
	init_waitqueue_head(&conf->wait_barrier);



	bio_list_init(&conf->pending_bio_list);

	conf->pending_count = 0;



	conf->last_used = -1;

	for (i = 0; i < conf->raid_disks; i++) {
@@ -2776,3 +2794,5 @@ MODULE_DESCRIPTION("RAID1 (mirroring) personality for MD"); 
MODULE_ALIAS("md-personality-3"); /* RAID1 */

MODULE_ALIAS("md-raid1");

MODULE_ALIAS("md-level-1");



module_param(max_queued_requests, int, S_IRUGO|S_IWUSR);

drivers/md/raid1.h

+1 −0
Original line number Diff line number Diff line
@@ -46,6 +46,7 @@ struct r1conf { 


	/* queue pending writes to be submitted on unplug */

	struct bio_list		pending_bio_list;

	int			pending_count;



	/* for use when syncing mirrors:

	 * We don't allow both normal IO and resync/recovery IO at

drivers/md/raid10.c

+20 −0
Original line number Diff line number Diff line
@@ -58,6 +58,12 @@ 
 */

#define	NR_RAID10_BIOS 256



/* When there are this many requests queue to be written by

 * the raid10 thread, we become 'congested' to provide back-pressure

 * for writeback.

 */

static int max_queued_requests = 1024;



static void allow_barrier(struct r10conf *conf);

static void lower_barrier(struct r10conf *conf);
@@ -681,6 +687,10 @@ static int raid10_congested(void *data, int bits) 
	struct r10conf *conf = mddev->private;

	int i, ret = 0;



	if ((bits & (1 << BDI_async_congested)) &&

	    conf->pending_count >= max_queued_requests)

		return 1;



	if (mddev_congested(mddev, bits))

		return 1;

	rcu_read_lock();
@@ -706,10 +716,12 @@ static void flush_pending_writes(struct r10conf *conf) 
	if (conf->pending_bio_list.head) {

		struct bio *bio;

		bio = bio_list_get(&conf->pending_bio_list);

		conf->pending_count = 0;

		spin_unlock_irq(&conf->device_lock);

		/* flush any pending bitmap writes to disk

		 * before proceeding w/ I/O */

		bitmap_unplug(conf->mddev->bitmap);

		wake_up(&conf->wait_barrier);



		while (bio) { /* submit pending writes */

			struct bio *next = bio->bi_next;
@@ -996,6 +1008,11 @@ read_again: 
	/*

	 * WRITE:

	 */

	if (conf->pending_count >= max_queued_requests) {

		md_wakeup_thread(mddev->thread);

		wait_event(conf->wait_barrier,

			   conf->pending_count < max_queued_requests);

	}

	/* first select target devices under rcu_lock and

	 * inc refcount on their rdev.  Record them by setting

	 * bios[x] to bio
@@ -1129,6 +1146,7 @@ retry_write: 
		atomic_inc(&r10_bio->remaining);

		spin_lock_irqsave(&conf->device_lock, flags);

		bio_list_add(&conf->pending_bio_list, mbio);

		conf->pending_count++;

		spin_unlock_irqrestore(&conf->device_lock, flags);

	}
@@ -3086,3 +3104,5 @@ MODULE_DESCRIPTION("RAID10 (striped mirror) personality for MD"); 
MODULE_ALIAS("md-personality-9"); /* RAID10 */

MODULE_ALIAS("md-raid10");

MODULE_ALIAS("md-level-10");



module_param(max_queued_requests, int, S_IRUGO|S_IWUSR);

drivers/md/raid10.h

+1 −1
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ struct r10conf { 
	struct list_head	retry_list;

	/* queue pending writes and submit them on unplug */

	struct bio_list		pending_bio_list;



	int			pending_count;



	spinlock_t		resync_lock;

	int nr_pending;

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