linux-kernel - Re: [PATCH] mm/memcg: support control THP behaviour in cgroup

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Date:   Wed, 18 May 2022 18:14:45 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     CGEL <cgel.zte@...il.com>
Cc:     Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Yang Shi <shy828301@...il.com>, Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Peter Xu <peterx@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Muchun Song <songmuchun@...edance.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        Yang Yang <yang.yang29@....com.cn>
Subject: Re: [PATCH] mm/memcg: support control THP behaviour in cgroup

On Wed, May 11, 2022 at 03:31:00AM +0000, CGEL wrote:
> On Tue, May 10, 2022 at 08:11:16PM -0700, Roman Gushchin wrote:
> > 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@...il.com> 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! If no other suggesting we will submit a bpf version of this patch.
>

What is your proposal for BPF? How do you intend to add attach points
(attach_type) for policy? Is it still going to be per cgroup?

Balbir Singh