linux-kernel - Re: [PATCH v2 13/23] mm: introduce bpf_out_of

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Message-ID: <aRG0ZyL93jWm4TAa@tiehlicka>
Date: Mon, 10 Nov 2025 10:46:15 +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 13/23] mm: introduce bpf_out_of_memory() BPF kfunc

On Mon 27-10-25 16:21:56, Roman Gushchin wrote:
> Introduce bpf_out_of_memory() bpf kfunc, which allows to declare
> an out of memory events and trigger the corresponding kernel OOM
> handling mechanism.
> 
> It takes a trusted memcg pointer (or NULL for system-wide OOMs)
> as an argument, as well as the page order.
> 
> If the BPF_OOM_FLAGS_WAIT_ON_OOM_LOCK flag is not set, only one OOM
> can be declared and handled in the system at once, so if the function
> is called in parallel to another OOM handling, it bails out with -EBUSY.
> This mode is suited for global OOM's: any concurrent OOMs will likely
> do the job and release some memory. In a blocking mode (which is
> suited for memcg OOMs) the execution will wait on the oom_lock mutex.

Rather than relying on BPF_OOM_FLAGS_WAIT_ON_OOM_LOCK would it make
sense to take the oom_lock based on the oc->memcg so that this is
completely transparent to specific oom bpf handlers?
-- 
Michal Hocko
SUSE Labs