linux-kernel - Re: oom killer and long-waiting processes

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Message-ID: <AANLkTinTm1kc1n_GS-nk6t46j1_ia8a8i0H7bHWlmVba@mail.gmail.com>
Date:	Fri, 11 Jun 2010 08:34:21 +0800
From:	Ryan Wang <openspace.wang@...il.com>
To:	rientjes@...gle.com, mulyadi.santosa@...il.com
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernelnewbies@...linux.org
Subject: Re: oom killer and long-waiting processes

2010/6/11 David Rientjes <rientjes@...gle.com>:
> On Thu, 10 Jun 2010, Ryan Wang wrote:
>
>> Hi all,
>>
>>         I have one question about oom killer:
>> If many processes dealing with network communications,
>> but due to bad network traffic, the processes have to wait
>> for a very long time. And meanwhile they may consume
>> some memeory separately for computation. The number
>> of such processes may be large.
>>
>>         I wonder whether oom killer will kill these processes
>> when the system is under high pressure?
>>
>
> The kernel can deal with "high pressure" quite well, but in some cases
> such as when all of your RAM or your memory controller is filled with
> anonymous memory and cannot be reclaimed, the oom killer may be called to
> kill "something".  It prefers to kill something that will free a large
> amount of memory to avoid having to subsequently kill additional tasks
> when it kills something small first.
>
> If there are tasks that you'd either like to protect from the oom killer
> or always prefer in oom conditions, you can influence its decision-making
> from userspace by tuning /proc/<pid>/oom_adj of the task in question.
> Users typically set an oom_adj value of "-17" to completely disable oom
> killing of pid (the kernel will even panic if it can't find anything
> killable as a result of this!), a value of "-16" to prefer that pid gets
> killed last, and a value of "15" to always prefer pid gets killed first.
>
> Lowering a /proc/<pid>/oom_adj value for a pid from its current value (it
> inherits its value from the parent, which is usually 0) is only allowed by
> root, more specifically, it may only be done by the CAP_SYS_RESOURCE
> capability.
>
> You can refer to Documentation/filesystems/proc.txt for information on
> oom_adj.
>

Thanks all!
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