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Subject: Re: [PATCH resend] memcg: introduce per-memcg reclaim interface
From:   Roman Gushchin <roman.gushchin@linux.dev>
In-Reply-To: <YkdrEG5FlL7Gq2Vi@cmpxchg.org>
Date:   Fri, 1 Apr 2022 14:21:52 -0700
Cc:     Yosry Ahmed <yosryahmed@google.com>,
        Michal Hocko <mhocko@kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        cgroups@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
        Jonathan Corbet <corbet@lwn.net>, Yu Zhao <yuzhao@google.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Wei Xu <weixugc@google.com>, Greg Thelen <gthelen@google.com>
Message-Id: <243A0156-D26A-47C9-982A-C8B0CDD69DA2@linux.dev>
References: <YkdrEG5FlL7Gq2Vi@cmpxchg.org>
To:     Johannes Weiner <hannes@cmpxchg.org>
Precedence: bulk

> On Apr 1, 2022, at 2:13 PM, Johannes Weiner <hannes@cmpxchg.org> wrote:
>=20
> =EF=BB=BFOn Fri, Apr 01, 2022 at 11:39:30AM -0700, Roman Gushchin wrote:
>> The interface you're proposing is not really extensible, so we'll likely n=
eed to
>> introduce a new interface like memory.reclaim_ext very soon. Why not crea=
te
>> an extensible API from scratch?
>>=20
>> I'm looking at cgroup v2 documentation which describes various interface f=
iles
>> formats and it seems like given the number of potential optional argument=
s
>> the best option is nested keyed (please, refer to the Interface Files sec=
tion).
>>=20
>> E.g. the format can be:
>> echo "1G type=3Dfile nodemask=3D1-2 timeout=3D30s" > memory.reclaim
>=20
> Yeah, that syntax looks perfect.
>=20
> But why do you think it's not extensible from the current patch? We
> can add those arguments one by one as we agree on them, and return
> -EINVAL if somebody passes an unknown parameter.
>=20
> It seems to me the current proposal is forward-compatible that way
> (with the current set of keyword pararms being the empty set :-))

It wasn=E2=80=99t obvious to me. We spoke about positional arguments and the=
n it wasn=E2=80=99t clear how to add them in a backward-compatible way. The l=
ast thing we want is a bunch of memory.reclaim* interfaces :)

So yeah, let=E2=80=99s just describe it properly in the documentation, no co=
de changes are needed.=