From: Shakeel Butt <shakeelb@google.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Linux MM <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Cgroups <cgroups@vger.kernel.org>,
David Rientjes <rientjes@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Greg Thelen <gthelen@google.com>,
Dragos Sbirlea <dragoss@google.com>,
Priya Duraisamy <padmapriyad@google.com>
Subject: Re: [RFC] memory reserve for userspace oom-killer
Date: Wed, 21 Apr 2021 07:13:45 -0700 [thread overview]
Message-ID: <CALvZod6oCBB6tDh5wABSwdHfcDzLX7S7cOTLp_4Qk4DCi50X_A@mail.gmail.com> (raw)
In-Reply-To: <YH/S2dVxk2le8SMw@dhcp22.suse.cz>
On Wed, Apr 21, 2021 at 12:23 AM Michal Hocko <mhocko@suse.com> wrote:
>
[...]
> > In our observation the global reclaim is very non-deterministic at the
> > tail and dramatically impacts the reliability of the system. We are
> > looking for a solution which is independent of the global reclaim.
>
> I believe it is worth purusing a solution that would make the memory
> reclaim more predictable. I have seen direct reclaim memory throttling
> in the past. For some reason which I haven't tried to examine this has
> become less of a problem with newer kernels. Maybe the memory access
> patterns have changed or those problems got replaced by other issues but
> an excessive throttling is definitely something that we want to address
> rather than work around by some user visible APIs.
>
I agree we want to address the excessive throttling but for everyone
on the machine and most importantly it is a moving target. The reclaim
code continues to evolve and in addition it has callbacks to diverse
sets of subsystems.
The user visible APIs is for one specific use-case i.e. oom-killer
which will indirectly help in reducing the excessive throttling.
[...]
> > So, the suggestion is to have a per-task flag to (1) indicate to not
> > throttle and (2) fail allocations easily on significant memory
> > pressure.
> >
> > For (1), the challenge I see is that there are a lot of places in the
> > reclaim code paths where a task can get throttled. There are
> > filesystems that block/throttle in slab shrinking. Any process can get
> > blocked on an unrelated page or inode writeback within reclaim.
> >
> > For (2), I am not sure how to deterministically define "significant
> > memory pressure". One idea is to follow the __GFP_NORETRY semantics
> > and along with (1) the userspace oom-killer will see ENOMEM more
> > reliably than stucking in the reclaim.
>
> Some of the interfaces (e.g. seq_file uses GFP_KERNEL reclaim strength)
> could be more relaxed and rather fail than OOM kill but wouldn't your
> OOM handler be effectivelly dysfunctional when not able to collect data
> to make a decision?
>
Yes it would be. Roman is suggesting to have a precomputed kill-list
(pidfds ready to send SIGKILL) and whenever oom-killer gets ENOMEM, it
would go with the kill-list. Though we are still contemplating the
ways and side-effects of preferably returning ENOMEM in slowpath for
oom-killer and in addition the complexity to maintain the kill-list
and keeping it up to date.
thanks,
Shakeel
next prev parent reply other threads:[~2021-04-21 14:14 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 1:44 [RFC] memory reserve for userspace oom-killer Shakeel Butt
2021-04-20 6:45 ` Michal Hocko
2021-04-20 16:04 ` Shakeel Butt
2021-04-21 7:16 ` Michal Hocko
2021-04-21 13:57 ` Shakeel Butt
2021-04-21 14:29 ` Michal Hocko
2021-04-22 12:33 ` [RFC PATCH] Android OOM helper proof of concept peter enderborg
2021-04-22 13:03 ` Michal Hocko
2021-05-05 0:37 ` [RFC] memory reserve for userspace oom-killer Shakeel Butt
2021-05-05 1:26 ` Suren Baghdasaryan
2021-05-05 2:45 ` Shakeel Butt
2021-05-05 2:59 ` Suren Baghdasaryan
2021-04-20 19:17 ` Roman Gushchin
2021-04-20 19:36 ` Suren Baghdasaryan
2021-04-21 1:18 ` Shakeel Butt
2021-04-21 2:58 ` Roman Gushchin
2021-04-21 13:26 ` Shakeel Butt
2021-04-21 19:04 ` Roman Gushchin
2021-04-21 7:23 ` Michal Hocko
2021-04-21 14:13 ` Shakeel Butt [this message]
2021-04-21 17:05 ` peter enderborg
2021-04-21 18:28 ` Shakeel Butt
2021-04-21 18:46 ` Peter.Enderborg
2021-04-21 19:18 ` Shakeel Butt
2021-04-22 5:38 ` Peter.Enderborg
2021-04-22 14:27 ` Shakeel Butt
2021-04-22 15:41 ` Peter.Enderborg
2021-04-22 13:08 ` Michal Hocko
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