Patch "blk-throttle: make sure expire time isn't too big" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

blk-throttle: make sure expire time isn't too big

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
blk-throttle-make-sure-expire-time-isn-t-too-big.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Shaohua Li <[email protected]>
Date: Mon, 27 Mar 2017 10:51:36 -0700
Subject: blk-throttle: make sure expire time isn't too big

From: Shaohua Li <[email protected]>

[ Upstream commit 06cceedcca67a93ac7f7aa93bbd9980c7496d14e ]

cgroup could be throttled to a limit but when all cgroups cross high limit, queue enters a higher state and so the group should be throttled to a higher limit. It's possible the cgroup is sleeping because of throttle and other cgroups don't dispatch IO any more. In this case, nobody can trigger current downgrade/upgrade logic. To fix this issue, we could either set up a timer to wakeup the cgroup if other cgroups are idle or make sure this cgroup doesn't sleep too long. Setting up a timer means we must change the timer very frequently. This patch chooses the latter. Making cgroup sleep time not too big wouldn't change cgroup bps/iops, but could make it wakeup more frequently, which isn't a big issue because throtl_slice * 8 is already quite big.

---
 block/blk-throttle.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

@@ -648,6 +648,17 @@ static void throtl_dequeue_tg(struct thr
 static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
 					  unsigned long expires)
 {
+	unsigned long max_expire = jiffies + 8 * throtl_slice;
+
+	/*
+	 * Since we are adjusting the throttle limit dynamically, the sleep
+	 * time calculated according to previous limit might be invalid. It's
+	 * possible the cgroup sleep time is very long and no other cgroups
+	 * have IO running so notify the limit changes. Make sure the cgroup
+	 * doesn't sleep too long to avoid the missed notification.
+	 */
+	if (time_after(expires, max_expire))
+		expires = max_expire;
 	mod_timer(&sq->pending_timer, expires);
 	throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
 		   expires - jiffies, jiffies);

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/blk-throttle-make-sure-expire-time-isn-t-too-big.patch