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@xxxxxxx>
### Diffstat output
./drivers/md/raid1.c | 169 ++++++++++++++++++++++---------------------
./include/linux/raid/raid1.h | 4 -
2 files changed, 92 insertions(+), 81 deletions(-)
diff ./drivers/md/raid1.c~current~ ./drivers/md/raid1.c
--- ./drivers/md/raid1.c~current~ 2005-11-28 10:11:52.000000000 +1100
+++ ./drivers/md/raid1.c 2005-11-28 10:12:17.000000000 +1100
@@ -51,6 +51,8 @@ static mdk_personality_t raid1_personali
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, r
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 *r
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
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);
}
@@ -592,30 +576,83 @@ static int raid1_issue_flush(request_que
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)
{
@@ -677,10 +714,7 @@ static int make_request(request_queue_t
*/
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));
@@ -908,13 +942,8 @@ 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;
@@ -1316,12 +1345,16 @@ static sector_t sync_request(mddev_t *md
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,
@@ -1354,10 +1387,6 @@ static sector_t sync_request(mddev_t *md
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;
@@ -1541,8 +1570,7 @@ 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);
@@ -1713,11 +1741,7 @@ static int raid1_reshape(mddev_t *mddev,
}
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;
@@ -1737,12 +1761,7 @@ static int raid1_reshape(mddev_t *mddev,
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);
@@ -1757,18 +1776,10 @@ static void raid1_quiesce(mddev_t *mddev
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) {
diff ./include/linux/raid/raid1.h~current~ ./include/linux/raid/raid1.h
--- ./include/linux/raid/raid1.h~current~ 2005-11-28 10:08:19.000000000 +1100
+++ ./include/linux/raid/raid1.h 2005-11-28 10:12:17.000000000 +1100
@@ -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;
-
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
