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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@kernel.org
Cc: linux-mm@kvack.org, rientjes@google.com,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	oleg@redhat.com
Subject: Re: [PATCH 2/3] oom, oom_reaper: Try to reap tasks which skip regular OOM killer path
Date: Mon, 11 Apr 2016 22:26:09 +0900	[thread overview]
Message-ID: <201604112226.IFC52662.FOFVtQSJLOFMOH@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20160411120238.GF23157@dhcp22.suse.cz>

Michal Hocko wrote:
> On Sat 09-04-16 13:39:30, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Fri 08-04-16 20:19:28, Tetsuo Handa wrote:
> > > > I looked at next-20160408 but I again came to think that we should remove
> > > > these shortcuts (something like a patch shown bottom).
> > >
> > > feel free to send the patch with the full description. But I would
> > > really encourage you to check the history to learn why those have been
> > > added and describe why those concerns are not valid/important anymore.
> > 
> > I believe that past discussions and decisions about current code are too
> > optimistic because they did not take 'The "too small to fail" memory-
> > allocation rule' problem into account.
> 
> In most cases they were driven by _real_ usecases though. And that
> is what matters. Theoretically possible issues which happen under
> crazy workloads which are DoSing the machine already are not something
> to optimize for. Sure we should try to cope with them as gracefully
> as possible, no questions about that, but we should try hard not to
> reintroduce previous issues during _sensible_ workloads.

I'm not requesting you to optimize for crazy workloads. None of my
customers intentionally put crazy workloads, but they are getting silent
hangups and I'm suspecting that something went wrong with memory management.
But there is no evidence because memory management subsystem remains silent.
You call my testcases DoS, but there is no evidence that my customers
are not hitting the same problem my testcases found.

I'm suggesting you to at least emit diagnostic messages when something went
wrong. That is what kmallocwd is for. And if you do not want to emit
diagnostic messages, I'm fine with timeout based approach.

WARNING: multiple messages have this Message-ID (diff)
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@kernel.org
Cc: linux-mm@kvack.org, rientjes@google.com,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	oleg@redhat.com
Subject: Re: [PATCH 2/3] oom, oom_reaper: Try to reap tasks which skip regular OOM killer path
Date: Mon, 11 Apr 2016 22:26:09 +0900	[thread overview]
Message-ID: <201604112226.IFC52662.FOFVtQSJLOFMOH@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20160411120238.GF23157@dhcp22.suse.cz>

Michal Hocko wrote:
> On Sat 09-04-16 13:39:30, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Fri 08-04-16 20:19:28, Tetsuo Handa wrote:
> > > > I looked at next-20160408 but I again came to think that we should remove
> > > > these shortcuts (something like a patch shown bottom).
> > >
> > > feel free to send the patch with the full description. But I would
> > > really encourage you to check the history to learn why those have been
> > > added and describe why those concerns are not valid/important anymore.
> > 
> > I believe that past discussions and decisions about current code are too
> > optimistic because they did not take 'The "too small to fail" memory-
> > allocation rule' problem into account.
> 
> In most cases they were driven by _real_ usecases though. And that
> is what matters. Theoretically possible issues which happen under
> crazy workloads which are DoSing the machine already are not something
> to optimize for. Sure we should try to cope with them as gracefully
> as possible, no questions about that, but we should try hard not to
> reintroduce previous issues during _sensible_ workloads.

I'm not requesting you to optimize for crazy workloads. None of my
customers intentionally put crazy workloads, but they are getting silent
hangups and I'm suspecting that something went wrong with memory management.
But there is no evidence because memory management subsystem remains silent.
You call my testcases DoS, but there is no evidence that my customers
are not hitting the same problem my testcases found.

I'm suggesting you to at least emit diagnostic messages when something went
wrong. That is what kmallocwd is for. And if you do not want to emit
diagnostic messages, I'm fine with timeout based approach.

--
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  reply	other threads:[~2016-04-11 13:26 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-06 14:13 [PATCH 0/3] oom reaper follow ups v1 Michal Hocko
2016-04-06 14:13 ` Michal Hocko
2016-04-06 14:13 ` [PATCH 1/3] mm, oom: move GFP_NOFS check to out_of_memory Michal Hocko
2016-04-06 14:13   ` Michal Hocko
2016-04-06 14:13 ` [PATCH 2/3] oom, oom_reaper: Try to reap tasks which skip regular OOM killer path Michal Hocko
2016-04-06 14:13   ` Michal Hocko
2016-04-07 11:38   ` Tetsuo Handa
2016-04-07 11:38     ` Tetsuo Handa
2016-04-08 11:19     ` Tetsuo Handa
2016-04-08 11:19       ` Tetsuo Handa
2016-04-08 11:50       ` Michal Hocko
2016-04-08 11:50         ` Michal Hocko
2016-04-09  4:39         ` [PATCH 2/3] oom, oom_reaper: Try to reap tasks which skipregular " Tetsuo Handa
2016-04-09  4:39           ` Tetsuo Handa
2016-04-11 12:02           ` Michal Hocko
2016-04-11 12:02             ` Michal Hocko
2016-04-11 13:26             ` Tetsuo Handa [this message]
2016-04-11 13:26               ` [PATCH 2/3] oom, oom_reaper: Try to reap tasks which skip regular " Tetsuo Handa
2016-04-11 13:43               ` Michal Hocko
2016-04-11 13:43                 ` Michal Hocko
2016-04-13 11:08                 ` Tetsuo Handa
2016-04-13 11:08                   ` Tetsuo Handa
2016-04-08 11:34     ` Michal Hocko
2016-04-08 11:34       ` Michal Hocko
2016-04-08 13:14   ` Michal Hocko
2016-04-08 13:14     ` Michal Hocko
2016-04-06 14:13 ` [PATCH 3/3] mm, oom_reaper: clear TIF_MEMDIE for all tasks queued for oom_reaper Michal Hocko
2016-04-06 14:13   ` Michal Hocko
2016-04-07 11:55   ` Tetsuo Handa
2016-04-07 11:55     ` Tetsuo Handa
2016-04-08 11:34     ` Michal Hocko
2016-04-08 11:34       ` Michal Hocko
2016-04-16  2:51       ` Tetsuo Handa
2016-04-17 11:54         ` Michal Hocko
2016-04-18 11:59           ` Tetsuo Handa
2016-04-19 14:17             ` Michal Hocko
2016-04-19 15:07               ` Tetsuo Handa
2016-04-19 19:32                 ` Michal Hocko
2016-04-08 13:07   ` Michal Hocko
2016-04-08 13:07     ` Michal Hocko

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