linux-kernel - Re: [PATCH v2 23/23] bpf: selftests: PSI struct ops test

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Message-ID: <aRG1AX0tQjAJU6lT@tiehlicka>
Date: Mon, 10 Nov 2025 10:48:49 +0100
From: Michal Hocko <mhocko@...e.com>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	Alexei Starovoitov <ast@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	JP Kobryn <inwardvessel@...il.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, bpf@...r.kernel.org,
	Martin KaFai Lau <martin.lau@...nel.org>,
	Song Liu <song@...nel.org>,
	Kumar Kartikeya Dwivedi <memxor@...il.com>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v2 23/23] bpf: selftests: PSI struct ops test

On Mon 27-10-25 16:22:06, Roman Gushchin wrote:
> Add a PSI struct ops test.
> 
> The test creates a cgroup with two child sub-cgroups, sets up
> memory.high for one of those and puts there a memory hungry
> process (initially frozen).
> 
> Then it creates 2 PSI triggers from within a init() BPF callback and
> attaches them to these cgroups.  Then it deletes the first cgroup,
> creates another one and runs the memory hungry task. From the cgroup
> creation callback the test is creating another trigger.
> 
> The memory hungry task is creating a high memory pressure in one
> memory cgroup, which triggers a PSI event. The PSI BPF handler
> declares a memcg oom in the corresponding cgroup. Finally the checks
> that both handle_cgroup_free() and handle_psi_event() handlers were
> executed, the correct process was killed and oom counters were
> updated.

I might be just dense but what is behind that deleted cgroup
(deleted_cgroup_id etc) dance?

-- 
Michal Hocko
SUSE Labs