Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever

[Vlastimil Babka]

On 07/10/2017 09:48 AM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> Tetsuo Handa has reported [1][2][3]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
> unusable.
> 
> 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.
> 
> [1] http://lkml.kernel.org/r/201602092349.ACG81273.OSVtMJQHLOFOFF@xxxxxxxxxxxxxxxxxxx
> [2] http://lkml.kernel.org/r/201702212335.DJB30777.JOFMHSFtVLQOOF@xxxxxxxxxxxxxxxxxxx
> [3] http://lkml.kernel.org/r/201706300914.CEH95859.FMQOLVFHJFtOOS@xxxxxxxxxxxxxxxxxxx
> 
> Acked-by: Mel Gorman <mgorman@xxxxxxx>
> Tested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Let's hope there won't be premature OOM's then.

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>