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From:   Shakeel Butt <shakeelb@google.com>
Date:   Wed, 4 Nov 2020 06:58:34 -0800
Message-ID: <CALvZod5Bdkvz+zWY1TsiVO2ApriC2dkOLAbcRn7A9mFzOCFs0w@mail.gmail.com>
Subject: Re: [PATCH rfc 1/3] mm: memcg: deprecate the non-hierarchical mode
To:     Roman Gushchin <guro@fb.com>
Cc:     Linux MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>, Tejun Heo <tj@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kernel Team <kernel-team@fb.com>
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On Tue, Nov 3, 2020 at 1:27 PM Roman Gushchin <guro@fb.com> wrote:
>
> The non-hierarchical cgroup v1 mode is a legacy of early days
> of the memory controller and doesn't bring any value today.
> However, it complicates the code and creates many edge cases
> all over the memory controller code.
>
> It's a good time to deprecate it completely.
>
> Functionally this patch enabled is by default for all cgroups
> and forbids switching it off. Nothing changes if cgroup v2 is used:
> hierarchical mode was enforced from scratch.
>
> To protect the ABI memory.use_hierarchy interface is preserved
> with a limited functionality: reading always returns "1", writing
> of "1" passes silently, writing of any other value fails with
> -EINVAL and a warning to dmesg (on the first occasion).
>
> Signed-off-by: Roman Gushchin <guro@fb.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>