linux-kernel - Re: [PATCH v2 15/23] mm: introduce bpf_task_is_oom

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Message-ID: <877bwevqxz.fsf@linux.dev>
Date: Tue, 28 Oct 2025 11:09:28 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Tejun Heo <tj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
  linux-kernel@...r.kernel.org,  Alexei Starovoitov <ast@...nel.org>,
  Suren Baghdasaryan <surenb@...gle.com>,  Michal Hocko
 <mhocko@...nel.org>,  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>
Subject: Re: [PATCH v2 15/23] mm: introduce bpf_task_is_oom_victim() kfunc

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

> On Mon, Oct 27, 2025 at 04:21:58PM -0700, Roman Gushchin wrote:
>> Export tsk_is_oom_victim() helper as a BPF kfunc.
>> It's very useful to avoid redundant oom kills.
>> 
>> Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
>> ---
>>  mm/oom_kill.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>> 
>> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
>> index 72a346261c79..90bb86dee3cf 100644
>> --- a/mm/oom_kill.c
>> +++ b/mm/oom_kill.c
>> @@ -1397,11 +1397,25 @@ __bpf_kfunc int bpf_out_of_memory(struct mem_cgroup *memcg__nullable,
>>  	return ret;
>>  }
>>  
>> +/**
>> + * bpf_task_is_oom_victim - Check if the task has been marked as an OOM victim
>> + * @task: task to check
>> + *
>> + * Returns true if the task has been previously selected by the OOM killer
>> + * to be killed. It's expected that the task will be destroyed soon and some
>> + * memory will be freed, so maybe no additional actions required.
>> + */
>> +__bpf_kfunc bool bpf_task_is_oom_victim(struct task_struct *task)
>> +{
>> +	return tsk_is_oom_victim(task);
>> +}
>
> In general, I'm not sure it's a good idea to add kfuncs for things which are
> trivially accessible. Why can't things like this be provided as BPF
> helpers?

I agree that this one might be too trivial, but I added it based on the
request from Michal Hocko. But with other helpers (e.g. for accessing
memcg stats) the idea is to provide a relatively stable interface for
bpf programs, which is not dependent on the implementation details. This
will simplify the maintenance of bpf programs across multiple kernel
versions.

Thanks!