From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f51.google.com (mail-oi0-f51.google.com [209.85.218.51]) by kanga.kvack.org (Postfix) with ESMTP id E38BF829BE for ; Fri, 13 Mar 2015 11:27:03 -0400 (EDT) Received: by oifu20 with SMTP id u20so20190220oif.11 for ; Fri, 13 Mar 2015 08:27:03 -0700 (PDT) Received: from mail-ob0-x22e.google.com (mail-ob0-x22e.google.com. [2607:f8b0:4003:c01::22e]) by mx.google.com with ESMTPS id ix8si1222449obc.59.2015.03.13.08.27.03 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 13 Mar 2015 08:27:03 -0700 (PDT) Received: by obcuz6 with SMTP id uz6so20414194obc.7 for ; Fri, 13 Mar 2015 08:27:03 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <5502F9BC.2020001@redhat.com> References: <5502F9BC.2020001@redhat.com> Date: Fri, 13 Mar 2015 20:57:03 +0530 Message-ID: Subject: Re: kswapd hogging in lowmem_shrink From: Vaibhav Shinde Content-Type: multipart/alternative; boundary=001a1135e1eae1d04805112d21fc Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Mel Gorman --001a1135e1eae1d04805112d21fc Content-Type: text/plain; charset=UTF-8 On Fri, Mar 13, 2015 at 8:22 PM, Rik van Riel 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. --001a1135e1eae1d04805112d21fc Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On F= ri, Mar 13, 2015 at 8:22 PM, Rik van Riel <riel@redhat.com> wr= ote:
On 03/13/2015 10:25 AM, Vaibhav S= hinde wrote:
>
> On low memory situation, I see various shrinkers being invoked, but in=
> lowmem_shrink() case, kswapd is found to be hogging for around 150msec= s.
>
> 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 it= s oom_score, I am using a embedded device with 2GB memory, there are task r= unning that cause lowmemory situation - no issue about it.

But my concern is kswapd takes too long to iterate through all the= processes(lowmem_shrink() =3D> for_each_process()), the time taken is a= round 150msec, due to which my high priority application suffer system late= ncy that cause malfunctioning.
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