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From: Roman Gushchin <roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>
Subject: Re: [PATCH] mm/memcg: support control THP behaviour in cgroup
Date: Tue, 10 May 2022 20:11:16 -0700
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To: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: CGEL <cgel.zte-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Yang Shi <shy828301-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Matthew Wilcox <willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Miaohe Lin <linmiaohe-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, William Kucharski <william.kucharski-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>, Peter Xu <peterx-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Hugh Dickins <hughd-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>, Muchun Song <songmuchun-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Suren Baghdasaryan <surenb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Linux Kernel Mailing List <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux MM <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Yang Yang <yang.yang29-Th6q7B73Y6EnDS1+zs4M5A@public.gmane.org>

On Tue, May 10, 2022 at 07:47:29PM -0700, Shakeel Butt wrote:
> On Tue, May 10, 2022 at 7:19 PM CGEL <cgel.zte-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >
> [...]
> > > > >
> > > > > All controls in cgroup v2 should be hierarchical. This is really
> > > > > required for a proper delegation semantic.
> > > > >
> > > >
> > > > Could we align to the semantic of /sys/fs/cgroup/memory.swappiness?
> > > > Some distributions like Ubuntu is still using cgroup v1.
> > >
> > > Other than enable flag, how would you handle the defrag flag
> > > hierarchically? It is much more complicated.
> >
> > Refer to memory.swappiness for cgroup, this new interface better be independent.
> 
> Let me give my 0.02. I buy the use-case of Admin restricting THPs to
> low priority jobs but I don't think memory controller is the right
> place to enforce that policy. Michal gave one way (prctl()) to enforce
> that policy. Have you explored the BPF way to enforce this policy?

+1 for bpf

I think these THP hints are too implementation-dependent and unstable to become
a part of cgroup API.

Thanks!