linux-kernel - Re: [RFC PATCH 0/3] Memory Controller eBPF support

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Message-ID: <aSckUNAfVokeC_2F@tiehlicka>
Date: Wed, 26 Nov 2025 17:01:20 +0100
From: Michal Hocko <mhocko@...e.com>
To: hui.zhu@...ux.dev
Cc: Roman Gushchin <roman.gushchin@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Shuah Khan <shuah@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>, Kees Cook <kees@...nel.org>,
	Tejun Heo <tj@...nel.org>, Jeff Xu <jeffxu@...omium.org>,
	mkoutny@...e.com, Jan Hendrik Farr <kernel@...rr.cc>,
	Christian Brauner <brauner@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Brian Gerst <brgerst@...il.com>,
	Masahiro Yamada <masahiroy@...nel.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org, Hui Zhu <zhuhui@...inos.cn>
Subject: Re: [RFC PATCH 0/3] Memory Controller eBPF support

On Wed 26-11-25 03:05:32, hui.zhu@...ux.dev wrote:
> 2025年11月25日 20:55, "Michal Hocko" <mhocko@...e.com mailto:mhocko@...e.com?to=%22Michal%20Hocko%22%20%3Cmhocko%40suse.com%3E > 写到:
> 
> 
> > 
> > On Tue 25-11-25 12:39:11, hui.zhu@...ux.dev wrote:
> > 
> > > 
> > > My goal is implement dynamic memory reclamation for memcgs without limits,
> > >  triggered by specific conditions.
> > >  
> > >  For instance, with memcg A and memcg B both unlimited, when memcg A faces
> > >  high PSI pressure, ebpf control memcg B do some memory reclaim work when
> > >  it try charge.
> > > 
> > Understood. Please also think whether this is already possible with
> > existing interfaces and if not what are roadblocks in that direction.
> 
> I think it's possible to implement a userspace program using the existing
> PSI userspace interfaces and the control interfaces provided by memcg to
> accomplish this task.
> However, this approach has several limitations:
> the entire process depends on the continuous execution of the userspace
> program, response latency is higher, and we cannot perform fine-grained
> operations on target memcg.

I will need to back these arguments by some actual numbers.

> Now that Roman has provided PSI eBPF functionality at
> https://lore.kernel.org/lkml/20251027231727.472628-1-roman.gushchin@linux.dev/
> Maybe we could add eBPF support to memcg as well, allowing us to implement
> the entire functionality directly in the kernel through eBPF.

His usecase is very specific to OOM handling and we have agreed that
this specific usecase is really tricky to achieve from userspace. I
haven't see sound arguments for this usecase yet.
-- 
Michal Hocko
SUSE Labs