From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Down <chris-6Bi1550iOqEnzZ6mRAm98g@public.gmane.org>
Subject: Re: Memory CG and 5.1 to 5.6 uprade slows backup
Date: Thu, 9 Apr 2020 18:50:44 +0100
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To: Bruno =?iso-8859-1?Q?Pr=E9mont?= <bonbons-ud5FBsm0p/xEiooADzr8i9i2O/JbrIOy@public.gmane.org>
Cc: Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Vladimir Davydov <vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

Bruno Pr=E9mont writes:
>On Thu, 9 Apr 2020 16:24:17 +0100 wrote:
>
>> Bruno Pr=E9mont writes:
>> >Could it be that cache is being prevented from being reclaimed by a task
>> >in another cgroup?
>> >
>> >e.g.
>> >  cgroup/system/backup
>> >    first reads $files (reads each once)
>> >  cgroup/workload/bla
>> >    second&more reads $files
>> >
>> >Would $files remain associated to cgroup/system/backup and not
>> >reclaimed there instead of being reassigned to cgroup/workload/bla?
>>
>> Yes, that's entirely possible. The first cgroup to fault in the pages is
>> charged for the memory. Other cgroups may use them, but they are not acc=
ounted
>> for as part of that other cgroup. They may also still be "active" as a r=
esult
>> of use by another cgroup.
>
>But the memory would then be 'active' in the original cgroup? which is
>not the case here I feel.

Yes, that's correct. I don't think it's the case here (since active_file is=
 not=20
that large in the affected cgroup), but it's certainly generally a possibil=
ity.