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Date:   Tue, 10 May 2022 20:11:16 -0700
From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Shakeel Butt <shakeelb@google.com>
Cc:     CGEL <cgel.zte@gmail.com>, Yang Shi <shy828301@gmail.com>,
        Michal Hocko <mhocko@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Matthew Wilcox <willy@infradead.org>,
        Miaohe Lin <linmiaohe@huawei.com>,
        William Kucharski <william.kucharski@oracle.com>,
        Peter Xu <peterx@redhat.com>, Hugh Dickins <hughd@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Muchun Song <songmuchun@bytedance.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Cgroups <cgroups@vger.kernel.org>,
        Yang Yang <yang.yang29@zte.com.cn>
Subject: Re: [PATCH] mm/memcg: support control THP behaviour in cgroup
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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@gmail.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!