[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: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 713dc9c..50bd7b1 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -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 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 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 @@
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_event_lock_irq(conf->wait_resume, conf->barrier < RESYNC_DEPTH,
- conf->resync_lock, unplug_slaves(conf->mddev));
- conf->next_resync = sect;
+ /* 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--;
+ }
+ 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 @@
* 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 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 @@
* 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 @@
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 @@
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 @@
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)) {