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[PATCH] md: improve raid10 "IO Barrier" concept
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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: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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NeilBrown authored and Linus Torvalds committed Jan 6, 2006
1 parent 17999be commit 0a27ec9
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Showing 2 changed files with 81 additions and 58 deletions.
135 changes: 79 additions & 56 deletions drivers/md/raid10.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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);
Expand All @@ -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)
Expand Down Expand Up @@ -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);
}

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--;
}
wait_event_lock_irq(conf->wait_resume, conf->barrier < RESYNC_DEPTH,
conf->resync_lock, unplug_slaves(conf->mddev));
conf->next_resync = sect;
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;
Expand Down Expand Up @@ -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));
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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)) {
Expand Down
4 changes: 2 additions & 2 deletions include/linux/raid/raid10.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down

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