linux-kernel - Re: kswapd hogging in lowmem

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Date:	Mon, 16 Mar 2015 07:43:50 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Vaibhav Shinde <v.bhav.shinde@...il.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: kswapd hogging in lowmem_shrink

On 03/16/2015 03:45 AM, Vaibhav Shinde wrote:
> 
> 
> On Fri, Mar 13, 2015 at 7:52 AM, Rik van Riel <riel@...hat.com
> <mailto:riel@...hat.com>> wrote:
>>
>> On 03/13/2015 10:25 AM, Vaibhav Shinde wrote:
>> >
>> > On low memory situation, I see various shrinkers being invoked, but in
>> > lowmem_shrink() case, kswapd is found to be hogging for around 150msecs.
>> >
>> > Due to this my application suffer latency issue, as the cpu was not
>> > released by kswapd0.
>> >
>> > I took below traces with vmscan events, that show lowmem_shrink taking
>> > such long time for execution.
>>
>> This is the Android low memory killer, which kills the
>> task with the lowest priority in the system.
>>
>> The low memory killer will iterate over all the tasks
>> in the system to identify the task to kill.
>>
>> This is not a problem in Android systems, and other
>> small systems where this piece of code is used.
>>
>> What kind of system are you trying to use the low
>> memory killer on?
>>
>> How many tasks are you running?
>>
> yes, lowmemorykiller kills the task depending on its oom_score, I am
> using a embedded device with 2GB memory, there are task running that
> cause lowmemory situation - no issue about it.
> 
> But my concern is kswapd takes too long to iterate through all the
> processes(lowmem_shrink() => for_each_process()), the time taken is
> around 150msec, due to which my high priority application suffer system
> latency that cause malfunctioning.

If it is an issue for you, you will have to fix that.

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