From: Michal Hocko <mhocko@suse.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Vasily Averin <vvs@virtuozzo.com>, Roman Gushchin <guro@fb.com>,
Uladzislau Rezki <urezki@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
Shakeel Butt <shakeelb@google.com>,
Mel Gorman <mgorman@techsingularity.net>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, kernel@openvz.org,
Johannes Weiner <hannes@cmpxchg.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH memcg v3 2/3] mm, oom: do not trigger out_of_memory from the #PF
Date: Tue, 26 Oct 2021 16:07:41 +0200 [thread overview]
Message-ID: <YXgLrQwC/gKZAusv@dhcp22.suse.cz> (raw)
In-Reply-To: <62a326bc-37d2-b8c9-ddbf-7adaeaadf341@i-love.sakura.ne.jp>
On Tue 26-10-21 22:56:44, Tetsuo Handa wrote:
> On 2021/10/25 17:04, Michal Hocko wrote:
> > I do not think there is any guarantee. This code has meant to be a
> > safeguard but it turns out to be adding more harm than a safety. There
> > are several scenarios mentioned in this thread where this would be
> > counter productive or outright wrong thing to do.
>
> Setting PR_IO_FLUSHER via prctl(PR_SET_IO_FLUSHER) + hitting legacy kmem
> charge limit might be an unexpected combination?
I am not sure I follow or why PR_SET_IO_FLUSHER should be relevant. But
triggering the global OOM killer on kmem charge limit failure is
certainly not the right thing to do. Quite opposite because this would
be effectivelly a global DoS as a result of a local memory constrain.
> > On the other hand it is hard to imagine any legitimate situation where
> > this would be a right thing to do. Maybe you have something more
> > specific in mind? What would be the legit code to rely on OOM handling
> > out of the line (where the details about the allocation scope is lost)?
>
> I don't have specific scenario, but I feel that it might be a chance to
> retry killable vmalloc(). Commit b8c8a338f75e ("Revert "vmalloc: back off
> when the current task is killed"") was 4.5 years ago, and fuzz testing found
> many bugs triggered by memory allocation fault injection. Thus, I think that
> the direction is going towards "we can fail memory allocation upon SIGKILL
> (rather than worrying about depleting memory reserves and/or escalating to
> global OOM killer invocations)". Most memory allocation requests which
> allocate memory for userspace process are willing to give up upon SIGKILL.
>
> Like you are trying to add NOFS, NOIO, NOFAIL support to vmalloc(), you could
> consider KILLABLE support as well. Of course, direct reclaim makes it difficult
> to immediately give up upon SIGKILL, but killable allocation sounds still nice
> even if best-effort basis.
This is all fine but I am not sure how this is realated to this patch.
The previous patch already gives up in pagefault_out_of_memory on fatal
signal pending. So this code is not really reachable.
Also alowing more allocations to fail doesn't really suggest that we
should trigger OOM killer from #PF. I would argue that the opposite is
the case actually. Or I just haven't understood your concern?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-10-26 14:07 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-18 8:13 [PATCH memcg 0/1] false global OOM triggered by memcg-limited task Vasily Averin
2021-10-18 9:04 ` Michal Hocko
2021-10-18 10:05 ` Vasily Averin
2021-10-18 10:12 ` Vasily Averin
2021-10-18 11:53 ` Michal Hocko
[not found] ` <27dc0c49-a0d6-875b-49c6-0ef5c0cc3ac8@virtuozzo.com>
2021-10-18 12:27 ` Michal Hocko
2021-10-18 15:07 ` Shakeel Butt
2021-10-18 16:51 ` Michal Hocko
2021-10-18 17:13 ` Shakeel Butt
2021-10-18 18:52 ` Vasily Averin
2021-10-18 19:18 ` Vasily Averin
2021-10-19 5:34 ` Shakeel Butt
2021-10-19 5:33 ` Shakeel Butt
2021-10-19 6:42 ` Vasily Averin
2021-10-19 8:47 ` Michal Hocko
2021-10-19 6:30 ` Vasily Averin
2021-10-19 8:49 ` Michal Hocko
2021-10-19 10:30 ` Vasily Averin
2021-10-19 11:54 ` Michal Hocko
2021-10-19 12:04 ` Michal Hocko
2021-10-19 13:26 ` Vasily Averin
2021-10-19 14:13 ` Michal Hocko
2021-10-19 14:19 ` Michal Hocko
2021-10-19 19:09 ` Vasily Averin
2021-10-20 8:07 ` [PATCH memcg v4] memcg: prohibit unconditional exceeding the limit of dying tasks Vasily Averin
2021-10-20 8:43 ` Michal Hocko
2021-10-20 12:11 ` [PATCH memcg RFC 0/3] " Vasily Averin
[not found] ` <cover.1634730787.git.vvs@virtuozzo.com>
2021-10-20 12:12 ` [PATCH memcg 1/3] mm: do not firce global OOM from inside " Vasily Averin
2021-10-20 12:33 ` Michal Hocko
2021-10-20 13:52 ` Vasily Averin
2021-10-20 12:13 ` [PATCH memcg 2/3] memcg: remove charge forcinig for " Vasily Averin
2021-10-20 12:41 ` Michal Hocko
2021-10-20 14:21 ` Vasily Averin
2021-10-20 14:57 ` Michal Hocko
2021-10-20 15:20 ` Tetsuo Handa
2021-10-21 10:03 ` Michal Hocko
2021-10-20 12:14 ` [PATCH memcg 3/3] memcg: handle memcg oom failures Vasily Averin
2021-10-20 13:02 ` Michal Hocko
2021-10-20 15:46 ` Vasily Averin
2021-10-21 11:49 ` Michal Hocko
2021-10-21 15:05 ` Vasily Averin
2021-10-21 16:47 ` Michal Hocko
2021-10-22 8:10 ` [PATCH memcg v2 0/2] memcg: prohibit unconditional exceeding the limit of dying tasks Vasily Averin
[not found] ` <cover.1634889066.git.vvs@virtuozzo.com>
2021-10-22 8:11 ` [PATCH memcg v2 1/2] mm, oom: do not trigger out_of_memory from the #PF Vasily Averin
2021-10-22 8:55 ` Michal Hocko
2021-10-22 8:11 ` [PATCH memcg v2 2/2] memcg: prohibit unconditional exceeding the limit of dying tasks Vasily Averin
2021-10-22 9:10 ` Michal Hocko
2021-10-23 13:18 ` [PATCH memcg v3 0/3] " Vasily Averin
[not found] ` <cover.1634994605.git.vvs@virtuozzo.com>
2021-10-23 13:19 ` [PATCH memcg v3 1/3] mm, oom: pagefault_out_of_memory: don't force global OOM for " Vasily Averin
2021-10-25 9:27 ` Michal Hocko
2021-10-23 13:20 ` [PATCH memcg v3 2/3] mm, oom: do not trigger out_of_memory from the #PF Vasily Averin
2021-10-23 15:01 ` Tetsuo Handa
2021-10-23 19:15 ` Vasily Averin
2021-10-25 8:04 ` Michal Hocko
2021-10-26 13:56 ` Tetsuo Handa
2021-10-26 14:07 ` Michal Hocko [this message]
2021-10-25 9:34 ` Michal Hocko
2021-10-23 13:20 ` [PATCH memcg v3 3/3] memcg: prohibit unconditional exceeding the limit of dying tasks Vasily Averin
2021-10-25 9:36 ` Michal Hocko
2021-10-27 22:36 ` Andrew Morton
2021-10-28 7:22 ` Vasily Averin
2021-10-29 7:46 ` Greg Kroah-Hartman
2021-10-29 7:58 ` Michal Hocko
2021-10-21 8:03 ` [PATCH memcg 0/1] false global OOM triggered by memcg-limited task Vasily Averin
2021-10-21 11:49 ` Michal Hocko
2021-10-21 13:24 ` Vasily Averin
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