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authorNeilBrown <neilb@suse.de>2006-01-06 00:20:12 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-01-06 08:34:01 -0800
commit17999be4aa408e7ff3b9d32c735649676567a3cd (patch)
tree14f9fd4ef0299f16274ce2980baef7b96f111bea /drivers/md
parentac81b2ee45eb811fdb0aa1cfb71d468d944d00ce (diff)
downloadop-kernel-dev-17999be4aa408e7ff3b9d32c735649676567a3cd.zip
op-kernel-dev-17999be4aa408e7ff3b9d32c735649676567a3cd.tar.gz
[PATCH] md: improve raid1 "IO Barrier" concept
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>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/raid1.c167
1 files changed, 89 insertions, 78 deletions
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 229d7b2..f520414 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -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 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--;
}
- wait_event_lock_irq(conf->wait_resume, conf->barrier < RESYNC_DEPTH,
- conf->resync_lock, raid1_unplug(conf->mddev->queue));
- 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);
+}
+
+
/* 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) {
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