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 16:24:17 +0100
Message-ID: <20200409152417.GB1040020@chrisdown.name>
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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:
>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=20
charged for the memory. Other cgroups may use them, but they are not accoun=
ted=20
for as part of that other cgroup. They may also still be "active" as a resu=
lt=20
of use by another cgroup.