netdev - Re: [PATCH bpf-next v3 00/13] bpf: Introduce selectable memcg for bpf map

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Date:   Thu, 8 Sep 2022 10:44:18 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Zefan Li <lizefan.x@...edance.com>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH bpf-next v3 00/13] bpf: Introduce selectable memcg for bpf map

On Thu, Sep 8, 2022 at 1:01 AM Tejun Heo <tj@...nel.org> wrote:
>
> On Wed, Sep 07, 2022 at 09:27:09AM -0700, Alexei Starovoitov wrote:
> > On Wed, Sep 7, 2022 at 9:18 AM Tejun Heo <tj@...nel.org> wrote:
> > >
> > > Hello,
> > >
> > > On Wed, Sep 07, 2022 at 09:13:09AM -0700, Alexei Starovoitov wrote:
> > > > Hmm. We discussed this option already. We definitely don't want
> > > > to introduce an uapi knob that will allow anyone to skip memcg
> > > > accounting today and in the future.
> > >
> > > cgroup.memory boot parameter is how memcg provides last-resort workarounds
> > > for this sort of problems / regressions while they're being addressed. It's
> > > not a dynamically changeable or programmable thing. Just a boot time
> > > opt-out. That said, if you don't want it, you don't want it.
> >
> > ahh. boot param.
> > Are you suggesting a global off switch ? Like nosocket and nokmem.
> > That would be a different story.
> > Need to think more about it. It could be ok.
>
> Yeah, nobpf or sth like that. An equivalent cgroup.memory parameter.
>

It may be a useful feature for some cases, but it can't help container users.
The memcg works well to limit the non-pinned bpf-map, that's the
reason why we, a container user, switch to memcg-based bpf charging.
Our goal is to make it also work for pinned bpf-map.

That said,  your proposal may be a useful feature,  but it should be
another different patchset.

-- 
Regards
Yafang