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[PATCH] md: improve raid1 "IO Barrier" concept

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raid1 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>
This commit is contained in:
NeilBrown 2006-01-06 00:20:12 -08:00 committed by Linus Torvalds
parent ac81b2ee45
commit 17999be4aa
2 changed files with 92 additions and 81 deletions
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167
drivers/md/raid1.c
View File

@ -51,6 +51,8 @@ static mdk_personality_t raid1_personality;
static void unplug_slaves(mddev_t *mddev);
static void allow_barrier(conf_t *conf);
static void lower_barrier(conf_t *conf);
static void * r1bio_pool_alloc(gfp_t gfp_flags, void *data)
{
@ -160,20 +162,13 @@ static void put_all_bios(conf_t *conf, r1bio_t *r1_bio)
static inline void free_r1bio(r1bio_t *r1_bio)
{
unsigned long flags;
conf_t *conf = mddev_to_conf(r1_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, r1_bio);
mempool_free(r1_bio, conf->r1bio_pool);
@ -182,22 +177,10 @@ static inline void free_r1bio(r1bio_t *r1_bio)
static inline void put_buf(r1bio_t *r1_bio)
{
conf_t *conf = mddev_to_conf(r1_bio->mddev);
unsigned long flags;
mempool_free(r1_bio, conf->r1buf_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(r1bio_t *r1_bio)
@ -210,6 +193,7 @@ static void reschedule_retry(r1bio_t *r1_bio)
list_add(&r1_bio->retry_list, &conf->retry_list);
spin_unlock_irqrestore(&conf->device_lock, flags);
wake_up(&conf->wait_barrier);
md_wakeup_thread(mddev->thread);
}
@ -593,30 +577,83 @@ static int raid1_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, raid1_unplug(conf->mddev->queue));
if (!conf->barrier++) {
wait_event_lock_irq(conf->wait_idle, !conf->nr_pending,
conf->resync_lock, raid1_unplug(conf->mddev->queue));
if (conf->nr_pending)
BUG();
}
wait_event_lock_irq(conf->wait_resume, conf->barrier < RESYNC_DEPTH,
conf->resync_lock, raid1_unplug(conf->mddev->queue));
conf->next_resync = sect;
/* Wait until no block IO is waiting */
wait_event_lock_irq(conf->wait_barrier, !conf->nr_waiting,
conf->resync_lock,
raid1_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,
raid1_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,
raid1_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);
}
/* duplicate the data pages for behind I/O */
static struct page **alloc_behind_pages(struct bio *bio)
{
@ -678,10 +715,7 @@ static int make_request(request_queue_t *q, struct bio * bio)
*/
md_write_start(mddev, bio); /* wait on superblock update early */
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));
@ -909,13 +943,8 @@ 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, raid1_unplug(conf->mddev->queue));
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->r1buf_pool);
conf->r1buf_pool = NULL;
@ -1317,12 +1346,16 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
return sync_blocks;
}
/*
* If there is non-resync activity waiting for us then
* put in a delay to throttle resync.
* If there is non-resync activity waiting for a turn,
* and resync is going fast enough,
* then let it though before starting on this new sync request.
*/
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;
/*
* If reconstructing, and >1 working disc,
@ -1355,10 +1388,6 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
r1_bio = mempool_alloc(conf->r1buf_pool, GFP_NOIO);
spin_lock_irq(&conf->resync_lock);
conf->nr_pending++;
spin_unlock_irq(&conf->resync_lock);
r1_bio->mddev = mddev;
r1_bio->sector = sector_nr;
r1_bio->state = 0;
@ -1542,8 +1571,7 @@ static int run(mddev_t *mddev)
mddev->recovery_cp = MaxSector;
spin_lock_init(&conf->resync_lock);
init_waitqueue_head(&conf->wait_idle);
init_waitqueue_head(&conf->wait_resume);
init_waitqueue_head(&conf->wait_barrier);
bio_list_init(&conf->pending_bio_list);
bio_list_init(&conf->flushing_bio_list);
@ -1714,11 +1742,7 @@ static int raid1_reshape(mddev_t *mddev, int raid_disks)
}
memset(newmirrors, 0, sizeof(struct mirror_info)*raid_disks);
spin_lock_irq(&conf->resync_lock);
conf->barrier++;
wait_event_lock_irq(conf->wait_idle, !conf->nr_pending,
conf->resync_lock, raid1_unplug(mddev->queue));
spin_unlock_irq(&conf->resync_lock);
raise_barrier(conf);
/* ok, everything is stopped */
oldpool = conf->r1bio_pool;
@ -1738,12 +1762,7 @@ static int raid1_reshape(mddev_t *mddev, int raid_disks)
conf->raid_disks = mddev->raid_disks = raid_disks;
conf->last_used = 0; /* just make sure it is in-range */
spin_lock_irq(&conf->resync_lock);
conf->barrier--;
spin_unlock_irq(&conf->resync_lock);
wake_up(&conf->wait_resume);
wake_up(&conf->wait_idle);
lower_barrier(conf);
set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
md_wakeup_thread(mddev->thread);
@ -1758,18 +1777,10 @@ static void raid1_quiesce(mddev_t *mddev, int state)
switch(state) {
case 1:
spin_lock_irq(&conf->resync_lock);
conf->barrier++;
wait_event_lock_irq(conf->wait_idle, !conf->nr_pending,
conf->resync_lock, raid1_unplug(mddev->queue));
spin_unlock_irq(&conf->resync_lock);
raise_barrier(conf);
break;
case 0:
spin_lock_irq(&conf->resync_lock);
conf->barrier--;
spin_unlock_irq(&conf->resync_lock);
wake_up(&conf->wait_resume);
wake_up(&conf->wait_idle);
lower_barrier(conf);
break;
}
if (mddev->thread) {

4
include/linux/raid/raid1.h
View File

@ -45,6 +45,7 @@ struct r1_private_data_s {
spinlock_t resync_lock;
int nr_pending;
int nr_waiting;
int barrier;
sector_t next_resync;
int fullsync; /* set to 1 if a full sync is needed,
@ -52,8 +53,7 @@ struct r1_private_data_s {
* Cleared when a sync completes.
*/
wait_queue_head_t wait_idle;
wait_queue_head_t wait_resume;
wait_queue_head_t wait_barrier;
struct pool_info *poolinfo;