linux-kernel - Re: [PATCH v1 1/3] mm: memcg: deprecate the non-hierarchical mode

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Message-ID: <20201112163119.GC873621@cmpxchg.org>
Date:   Thu, 12 Nov 2020 11:31:19 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
        David Rientjes <rientjes@...gle.com>, kernel-team@...com,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v1 1/3] mm: memcg: deprecate the non-hierarchical mode

On Tue, Nov 10, 2020 at 02:07:58PM -0800, Roman Gushchin 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@...com>
> Acked-by: Michal Hocko <mhocko@...e.com>
> Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
> Acked-by: David Rientjes <rientjes@...gle.com>

...and don't let the door hit you on the way out ;-)

Acked-by: Johannes Weiner <hannes@...xchg.org>