linux-kernel - Re: [PATCH] mm: terminate shrink

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Date:   Thu, 7 Dec 2017 07:46:07 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, hillf.zj@...baba-inc.com,
        minchan@...nel.org, mgorman@...hsingularity.net,
        ying.huang@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Tim Murray <timmurray@...gle.com>,
        Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH] mm: terminate shrink_slab loop if signal is pending

I'm, terribly sorry. My original code was checking for additional
condition which I realized is not useful here because it would mean
the signal was already processed. Should have missed the error while
removing it. Will address Michal's comments and fix the problem.

On Thu, Dec 7, 2017 at 1:58 AM, Michal Hocko <mhocko@...nel.org> wrote:
> On Thu 07-12-17 18:52:23, Sergey Senozhatsky wrote:
>> On (12/06/17 11:20), Suren Baghdasaryan wrote:
>> > Slab shrinkers can be quite time consuming and when signal
>> > is pending they can delay handling of the signal. If fatal
>> > signal is pending there is no point in shrinking that process
>> > since it will be killed anyway. This change checks for pending
>> > fatal signals inside shrink_slab loop and if one is detected
>> > terminates this loop early.
>> >
>> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
>> > ---
>> >  mm/vmscan.c | 7 +++++++
>> >  1 file changed, 7 insertions(+)
>> >
>> > diff --git a/mm/vmscan.c b/mm/vmscan.c
>> > index c02c850ea349..69296528ff33 100644
>> > --- a/mm/vmscan.c
>> > +++ b/mm/vmscan.c
>> > @@ -486,6 +486,13 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
>> >                     .memcg = memcg,
>> >             };
>> >
>> > +           /*
>> > +            * We are about to die and free our memory.
>> > +            * Stop shrinking which might delay signal handling.
>> > +            */
>> > +           if (unlikely(fatal_signal_pending(current))
>>
>> -               if (unlikely(fatal_signal_pending(current))
>> +               if (unlikely(fatal_signal_pending(current)))
>
> Heh, well, spotted. This begs a question how this has been tested, if at
> all?
> --
> Michal Hocko
> SUSE Labs