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authorNeilBrown <neilb@suse.de>2011-10-11 16:50:01 +1100
committerNeilBrown <neilb@suse.de>2011-10-11 16:50:01 +1100
commit34db0cd60f8a1f4ab73d118a8be3797c20388223 (patch)
tree45d1d629d6b9195d47d30980595686c9a3ee92f9 /drivers/md/raid1.c
parent84fc4b56db85cb9e05326424049973a2036c9940 (diff)
downloadlinux-34db0cd60f8a1f4ab73d118a8be3797c20388223.tar.bz2
md: add proper write-congestion reporting to RAID1 and RAID10.
RAID1 and RAID10 handle write requests by queuing them for handling by a separate thread. This is because when a write-intent-bitmap is active we might need to update the bitmap first, so it is good to queue a lot of writes, then do one big bitmap update for them all. However writeback request devices to appear to be congested after a while so it can make some guesstimate of throughput. The infinite queue defeats that (note that RAID5 has already has a finite queue so it doesn't suffer from this problem). So impose a limit on the number of pending write requests. By default it is 1024 which seems to be generally suitable. Make it configurable via module option just in case someone finds a regression. Signed-off-by: NeilBrown <neilb@suse.de>
Diffstat (limited to 'drivers/md/raid1.c')
-rw-r--r--drivers/md/raid1.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index e023a25acf54..d8957d74fd25 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -45,6 +45,11 @@
*/
#define NR_RAID1_BIOS 256
+/* When there are this many requests queue to be written by
+ * the raid1 thread, we become 'congested' to provide back-pressure
+ * for writeback.
+ */
+static int max_queued_requests = 1024;
static void allow_barrier(struct r1conf *conf);
static void lower_barrier(struct r1conf *conf);
@@ -598,6 +603,10 @@ int md_raid1_congested(struct mddev *mddev, int bits)
struct r1conf *conf = mddev->private;
int i, ret = 0;
+ if ((bits & (1 << BDI_async_congested)) &&
+ conf->pending_count >= max_queued_requests)
+ return 1;
+
rcu_read_lock();
for (i = 0; i < mddev->raid_disks; i++) {
struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
@@ -638,10 +647,12 @@ static void flush_pending_writes(struct r1conf *conf)
if (conf->pending_bio_list.head) {
struct bio *bio;
bio = bio_list_get(&conf->pending_bio_list);
+ conf->pending_count = 0;
spin_unlock_irq(&conf->device_lock);
/* flush any pending bitmap writes to
* disk before proceeding w/ I/O */
bitmap_unplug(conf->mddev->bitmap);
+ wake_up(&conf->wait_barrier);
while (bio) { /* submit pending writes */
struct bio *next = bio->bi_next;
@@ -945,6 +956,11 @@ read_again:
/*
* WRITE:
*/
+ if (conf->pending_count >= max_queued_requests) {
+ md_wakeup_thread(mddev->thread);
+ wait_event(conf->wait_barrier,
+ conf->pending_count < max_queued_requests);
+ }
/* first select target devices under rcu_lock and
* inc refcount on their rdev. Record them by setting
* bios[x] to bio
@@ -1108,6 +1124,7 @@ read_again:
atomic_inc(&r1_bio->remaining);
spin_lock_irqsave(&conf->device_lock, flags);
bio_list_add(&conf->pending_bio_list, mbio);
+ conf->pending_count++;
spin_unlock_irqrestore(&conf->device_lock, flags);
}
/* Mustn't call r1_bio_write_done before this next test,
@@ -2418,6 +2435,7 @@ static struct r1conf *setup_conf(struct mddev *mddev)
init_waitqueue_head(&conf->wait_barrier);
bio_list_init(&conf->pending_bio_list);
+ conf->pending_count = 0;
conf->last_used = -1;
for (i = 0; i < conf->raid_disks; i++) {
@@ -2776,3 +2794,5 @@ MODULE_DESCRIPTION("RAID1 (mirroring) personality for MD");
MODULE_ALIAS("md-personality-3"); /* RAID1 */
MODULE_ALIAS("md-raid1");
MODULE_ALIAS("md-level-1");
+
+module_param(max_queued_requests, int, S_IRUGO|S_IWUSR);