4.4-stable review patch. If anyone has any objections, please let me know.
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From: Shaohua Li shli@fb.com
[ 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.
Signed-off-by: Shaohua Li shli@fb.com Signed-off-by: Jens Axboe axboe@fb.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/blk-throttle.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
--- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -505,6 +505,17 @@ 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);