linux-kernel - Re: [PATCH v2] mm: Update mark

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Date: Wed, 21 Feb 2024 08:55:49 +0100
From: Michal Hocko <mhocko@...e.com>
To: Carlos Galo <carlosgalo@...gle.com>
Cc: rostedt@...dmis.org, akpm@...ux-foundation.org, surenb@...gle.com,
	android-mm@...gle.com, kernel-team@...roid.com,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: Update mark_victim tracepoints fields

Hi,
sorry I have missed this before.

On Thu 11-01-24 21:05:30, Carlos Galo wrote:
> The current implementation of the mark_victim tracepoint provides only
> the process ID (pid) of the victim process. This limitation poses
> challenges for userspace tools that need additional information
> about the OOM victim. The association between pid and the additional
> data may be lost after the kill, making it difficult for userspace to
> correlate the OOM event with the specific process.

You are correct that post OOM all per-process information is lost. On
the other hand we do dump all this information to the kernel log. Could
you explain why that is not suitable for your purpose?

> In order to mitigate this limitation, add the following fields:
> 
> - UID
>    In Android each installed application has a unique UID. Including
>    the `uid` assists in correlating OOM events with specific apps.
> 
> - Process Name (comm)
>    Enables identification of the affected process.
> 
> - OOM Score
>    Allows userspace to get additional insights of the relative kill
>    priority of the OOM victim.

What is the oom score useful for?

Is there any reason to provide a different information from the one
reported to the kernel log?
__oom_kill_process:
pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%hd\n",
                message, task_pid_nr(victim), victim->comm, K(mm->total_vm),
                K(get_mm_counter(mm, MM_ANONPAGES)),
                K(get_mm_counter(mm, MM_FILEPAGES)),
                K(get_mm_counter(mm, MM_SHMEMPAGES)),
                from_kuid(&init_user_ns, task_uid(victim)),
                mm_pgtables_bytes(mm) >> 10, victim->signal->oom_score_adj);

-- 
Michal Hocko
SUSE Labs