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

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Message-ID: <87wm6rwd4d.fsf@linux.dev>
Date: Mon, 25 Aug 2025 10:00:02 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Kumar Kartikeya Dwivedi <memxor@...il.com>,  linux-mm@...ck.org,
  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>,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 01/14] mm: introduce bpf struct ops for OOM handling

Martin KaFai Lau <martin.lau@...ux.dev> writes:

> On 8/20/25 5:24 PM, Roman Gushchin wrote:
>>> How is it decided who gets to run before the other? Is it based on
>>> order of attachment (which can be non-deterministic)?
>> Yeah, now it's the order of attachment.
>> 
>>> There was a lot of discussion on something similar for tc progs, and
>>> we went with specific flags that capture partial ordering constraints
>>> (instead of priorities that may collide).
>>> https://lore.kernel.org/all/20230719140858.13224-2-daniel@iogearbox.net
>>> It would be nice if we can find a way of making this consistent.
>
> +1
>
> The cgroup bpf prog has recently added the mprog api support also. If
> the simple order of attachment is not enough and needs to have
> specific ordering, we should make the bpf struct_ops support the same
> mprog api instead of asking each subsystem creating its own.
>
> fyi, another need for struct_ops ordering is to upgrade the
> BPF_PROG_TYPE_SOCK_OPS api to struct_ops for easier extension in the
> future. Slide 13 in
> https://drive.google.com/file/d/1wjKZth6T0llLJ_ONPAL_6Q_jbxbAjByp/view

Does it mean it's better now to keep it simple in the context of oom
patches with the plan to later reuse the generic struct_ops
infrastructure?

Honestly, I believe that the simple order of attachment should be
good enough for quite a while, so I'd not over-complicate this,
unless it's not fixable later.

Thanks!