Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever
From: Mel Gorman
Date: Thu Mar 09 2017 - 09:33:23 EST
On Tue, Mar 07, 2017 at 02:30:57PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> Tetsuo Handa has reported  that direct reclaimers might get stuck
> in too_many_isolated loop basically for ever because the last few pages
> on the LRU lists are isolated by the kswapd which is stuck on fs locks
> when doing the pageout or slab reclaim. This in turn means that there is
> nobody to actually trigger the oom killer and the system is basically
> too_many_isolated has been introduced by 35cd78156c49 ("vmscan: throttle
> direct reclaim when too many pages are isolated already") to prevent
> from pre-mature oom killer invocations because back then no reclaim
> progress could indeed trigger the OOM killer too early. But since the
> oom detection rework 0a0337e0d1d1 ("mm, oom: rework oom detection")
> the allocation/reclaim retry loop considers all the reclaimable pages
> and throttles the allocation at that layer so we can loosen the direct
> reclaim throttling.
> Make shrink_inactive_list loop over too_many_isolated bounded and returns
> immediately when the situation hasn't resolved after the first sleep.
> Replace congestion_wait by a simple schedule_timeout_interruptible because
> we are not really waiting on the IO congestion in this path.
> Please note that this patch can theoretically cause the OOM killer to
> trigger earlier while there are many pages isolated for the reclaim
> which makes progress only very slowly. This would be obvious from the oom
> report as the number of isolated pages are printed there. If we ever hit
> this should_reclaim_retry should consider those numbers in the evaluation
> in one way or another.
>  http://lkml.kernel.org/r/201602092349.ACG81273.OSVtMJQHLOFOFF@xxxxxxxxxxxxxxxxxxx
>  http://lkml.kernel.org/r/201702212335.DJB30777.JOFMHSFtVLQOOF@xxxxxxxxxxxxxxxxxxx
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>