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Commit 0a27ec96 authored by NeilBrown's avatar NeilBrown Committed by Linus Torvalds
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[PATCH] md: improve raid10 "IO Barrier" concept 



raid10 needs to put up a barrier to new requests while it does resync or other
background recovery.  The code for this is currently open-coded, slighty
obscure by its use of two waitqueues, and not documented.

This patch gathers all the related code into 4 functions, and includes a
comment which (hopefully) explains what is happening.

Signed-off-by: default avatarNeil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 17999be4

drivers/md/raid10.c

+79 −56
Original line number Diff line number Diff line
@@ -47,6 +47,9 @@ 


static void unplug_slaves(mddev_t *mddev);



static void allow_barrier(conf_t *conf);

static void lower_barrier(conf_t *conf);



static void * r10bio_pool_alloc(gfp_t gfp_flags, void *data)

{

	conf_t *conf = data;
@@ -175,20 +178,13 @@ static void put_all_bios(conf_t *conf, r10bio_t *r10_bio) 


static inline void free_r10bio(r10bio_t *r10_bio)

{

	unsigned long flags;



	conf_t *conf = mddev_to_conf(r10_bio->mddev);



	/*

	 * Wake up any possible resync thread that waits for the device

	 * to go idle.

	 */

	spin_lock_irqsave(&conf->resync_lock, flags);

	if (!--conf->nr_pending) {

		wake_up(&conf->wait_idle);

		wake_up(&conf->wait_resume);

	}

	spin_unlock_irqrestore(&conf->resync_lock, flags);

	allow_barrier(conf);



	put_all_bios(conf, r10_bio);

	mempool_free(r10_bio, conf->r10bio_pool);
@@ -197,22 +193,10 @@ static inline void free_r10bio(r10bio_t *r10_bio) 
static inline void put_buf(r10bio_t *r10_bio)

{

	conf_t *conf = mddev_to_conf(r10_bio->mddev);

	unsigned long flags;



	mempool_free(r10_bio, conf->r10buf_pool);



	spin_lock_irqsave(&conf->resync_lock, flags);

	if (!conf->barrier)

		BUG();

	--conf->barrier;

	wake_up(&conf->wait_resume);

	wake_up(&conf->wait_idle);



	if (!--conf->nr_pending) {

		wake_up(&conf->wait_idle);

		wake_up(&conf->wait_resume);

	}

	spin_unlock_irqrestore(&conf->resync_lock, flags);

	lower_barrier(conf);

}



static void reschedule_retry(r10bio_t *r10_bio)
@@ -640,30 +624,82 @@ static int raid10_issue_flush(request_queue_t *q, struct gendisk *disk, 
	return ret;

}



/*

 * Throttle resync depth, so that we can both get proper overlapping of

 * requests, but are still able to handle normal requests quickly.

/* Barriers....

 * Sometimes we need to suspend IO while we do something else,

 * either some resync/recovery, or reconfigure the array.

 * To do this we raise a 'barrier'.

 * The 'barrier' is a counter that can be raised multiple times

 * to count how many activities are happening which preclude

 * normal IO.

 * We can only raise the barrier if there is no pending IO.

 * i.e. if nr_pending == 0.

 * We choose only to raise the barrier if no-one is waiting for the

 * barrier to go down.  This means that as soon as an IO request

 * is ready, no other operations which require a barrier will start

 * until the IO request has had a chance.

 *

 * So: regular IO calls 'wait_barrier'.  When that returns there

 *    is no backgroup IO happening,  It must arrange to call

 *    allow_barrier when it has finished its IO.

 * backgroup IO calls must call raise_barrier.  Once that returns

 *    there is no normal IO happeing.  It must arrange to call

 *    lower_barrier when the particular background IO completes.

 */

#define RESYNC_DEPTH 32



static void device_barrier(conf_t *conf, sector_t sect)

static void raise_barrier(conf_t *conf)

{

	spin_lock_irq(&conf->resync_lock);

	wait_event_lock_irq(conf->wait_idle, !waitqueue_active(&conf->wait_resume),

			    conf->resync_lock, unplug_slaves(conf->mddev));



	if (!conf->barrier++) {

		wait_event_lock_irq(conf->wait_idle, !conf->nr_pending,

				    conf->resync_lock, unplug_slaves(conf->mddev));

		if (conf->nr_pending)

			BUG();

	/* Wait until no block IO is waiting */

	wait_event_lock_irq(conf->wait_barrier, !conf->nr_waiting,

			    conf->resync_lock,

			    raid10_unplug(conf->mddev->queue));



	/* block any new IO from starting */

	conf->barrier++;



	/* No wait for all pending IO to complete */

	wait_event_lock_irq(conf->wait_barrier,

			    !conf->nr_pending && conf->barrier < RESYNC_DEPTH,

			    conf->resync_lock,

			    raid10_unplug(conf->mddev->queue));



	spin_unlock_irq(&conf->resync_lock);

}

	wait_event_lock_irq(conf->wait_resume, conf->barrier < RESYNC_DEPTH,

			    conf->resync_lock, unplug_slaves(conf->mddev));

	conf->next_resync = sect;



static void lower_barrier(conf_t *conf)

{

	unsigned long flags;

	spin_lock_irqsave(&conf->resync_lock, flags);

	conf->barrier--;

	spin_unlock_irqrestore(&conf->resync_lock, flags);

	wake_up(&conf->wait_barrier);

}



static void wait_barrier(conf_t *conf)

{

	spin_lock_irq(&conf->resync_lock);

	if (conf->barrier) {

		conf->nr_waiting++;

		wait_event_lock_irq(conf->wait_barrier, !conf->barrier,

				    conf->resync_lock,

				    raid10_unplug(conf->mddev->queue));

		conf->nr_waiting--;

	}

	conf->nr_pending++;

	spin_unlock_irq(&conf->resync_lock);

}



static void allow_barrier(conf_t *conf)

{

	unsigned long flags;

	spin_lock_irqsave(&conf->resync_lock, flags);

	conf->nr_pending--;

	spin_unlock_irqrestore(&conf->resync_lock, flags);

	wake_up(&conf->wait_barrier);

}



static int make_request(request_queue_t *q, struct bio * bio)

{

	mddev_t *mddev = q->queuedata;
@@ -719,10 +755,7 @@ static int make_request(request_queue_t *q, struct bio * bio) 
	 * thread has put up a bar for new requests.

	 * Continue immediately if no resync is active currently.

	 */

	spin_lock_irq(&conf->resync_lock);

	wait_event_lock_irq(conf->wait_resume, !conf->barrier, conf->resync_lock, );

	conf->nr_pending++;

	spin_unlock_irq(&conf->resync_lock);

	wait_barrier(conf);



	disk_stat_inc(mddev->gendisk, ios[rw]);

	disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bio));
@@ -897,13 +930,8 @@ static void print_conf(conf_t *conf) 


static void close_sync(conf_t *conf)

{

	spin_lock_irq(&conf->resync_lock);

	wait_event_lock_irq(conf->wait_resume, !conf->barrier,

			    conf->resync_lock, 	unplug_slaves(conf->mddev));

	spin_unlock_irq(&conf->resync_lock);



	if (conf->barrier) BUG();

	if (waitqueue_active(&conf->wait_idle)) BUG();

	wait_barrier(conf);

	allow_barrier(conf);



	mempool_destroy(conf->r10buf_pool);

	conf->r10buf_pool = NULL;
@@ -1395,9 +1423,10 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i 
	 * If there is non-resync activity waiting for us then

	 * put in a delay to throttle resync.

	 */

	if (!go_faster && waitqueue_active(&conf->wait_resume))

	if (!go_faster && conf->nr_waiting)

		msleep_interruptible(1000);

	device_barrier(conf, sector_nr + RESYNC_SECTORS);

	raise_barrier(conf);

	conf->next_resync = sector_nr;



	/* Again, very different code for resync and recovery.

	 * Both must result in an r10bio with a list of bios that
@@ -1427,7 +1456,6 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i 


				r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);

				spin_lock_irq(&conf->resync_lock);

				conf->nr_pending++;

				if (rb2) conf->barrier++;

				spin_unlock_irq(&conf->resync_lock);

				atomic_set(&r10_bio->remaining, 0);
@@ -1500,10 +1528,6 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i 
		int count = 0;

		r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);



		spin_lock_irq(&conf->resync_lock);

		conf->nr_pending++;

		spin_unlock_irq(&conf->resync_lock);



		r10_bio->mddev = mddev;

		atomic_set(&r10_bio->remaining, 0);
@@ -1713,8 +1737,7 @@ static int run(mddev_t *mddev) 
	INIT_LIST_HEAD(&conf->retry_list);



	spin_lock_init(&conf->resync_lock);

	init_waitqueue_head(&conf->wait_idle);

	init_waitqueue_head(&conf->wait_resume);

	init_waitqueue_head(&conf->wait_barrier);



	/* need to check that every block has at least one working mirror */

	if (!enough(conf)) {

include/linux/raid/raid10.h

+2 −2
Original line number Diff line number Diff line
@@ -39,11 +39,11 @@ struct r10_private_data_s { 


	spinlock_t		resync_lock;

	int nr_pending;

	int nr_waiting;

	int barrier;

	sector_t		next_resync;



	wait_queue_head_t	wait_idle;

	wait_queue_head_t	wait_resume;

	wait_queue_head_t	wait_barrier;



	mempool_t *r10bio_pool;

	mempool_t *r10buf_pool;