linux-kernel - Re: [PATCH v1 01/14] mm: introduce bpf struct ops for OOM handling

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Message-ID: <87h5xi1e6p.fsf@linux.dev>
Date: Thu, 04 Sep 2025 07:32:14 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Tejun Heo <tj@...nel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,  Martin KaFai Lau
 <martin.lau@...ux.dev>,  Kumar Kartikeya Dwivedi <memxor@...il.com>,
  linux-mm <linux-mm@...ck.org>,  bpf <bpf@...r.kernel.org>,  Suren
 Baghdasaryan <surenb@...gle.com>,  Johannes Weiner <hannes@...xchg.org>,
  Michal Hocko <mhocko@...e.com>,  David Rientjes <rientjes@...gle.com>,
  Matt Bobrowski <mattbobrowski@...gle.com>,  Song Liu <song@...nel.org>,
  Alexei Starovoitov <ast@...nel.org>,  Andrew Morton
 <akpm@...ux-foundation.org>,  LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 01/14] mm: introduce bpf struct ops for OOM handling

Tejun Heo <tj@...nel.org> writes:

> Hello,
>
> On Wed, Sep 03, 2025 at 04:30:16PM -0700, Roman Gushchin wrote:
> ...
>> > - I'm passing in cgroup_id as an optional field in struct_ops and then in
>> >   enable path, look up the matching cgroup, verify it can attach there and
>> >   insert and update data structures accordingly:
>> >
>> >   https://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git/tree/kernel/sched/ext.c?h=scx-hier-prototype#n5280
>> 
>> Yeah, we discussed this option with Martin up in this thread. It doesn't
>> look as the best possible solution, but maybe the best we have at the moment.
>> 
>> Ideally, I want something like this:
>> 
>> void test_oom(void)
>> {
>> 	struct test_oom *skel;
>> 	int err, cgroup_fd;
>> 
>>         cgroup_fd = open(...);
>>         if (cgroup_fd < 0)
>> 		goto cleanup;
>> 
>> 	skel = test_oom__open_and_load();
>>         if (!skel)
>> 		goto cleanup;
>> 
>> 	err = test_oom__attach_cgroup(skel, cgroup_fd);
>> 	if (CHECK_FAIL(err))
>> 		goto cleanup;
>
> Yeah, that'd look better but are there practical differences? The only one I
> can think of is fs based permission check but that can be done separately
> too.

The practical difference is that a single struct ops can be attached
to multiple cgroups.