linux-kernel - Re: [PATCH] exit: add trace_task_exit() tracepoint before current->mm is reset

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Message-ID: <20250402095850.1f617dd4@gandalf.local.home>
Date: Wed, 2 Apr 2025 09:58:50 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Michal Hocko <mhocko@...e.com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>, Andrii Nakryiko
 <andrii@...nel.org>, linux-trace-kernel@...r.kernel.org,
 peterz@...radead.org, mingo@...nel.org, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, kernel-team@...a.com, oleg@...hat.com,
 brauner@...nel.org, glider@...gle.com, mhiramat@...nel.org,
 mathieu.desnoyers@...icios.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] exit: add trace_task_exit() tracepoint before
 current->mm is reset

On Wed, 2 Apr 2025 09:20:37 +0200
Michal Hocko <mhocko@...e.com> wrote:

> Is it important to tell the difference between thread and the
> whole process group exiting?
> 
> Please keep in mind that even group exit doesn't really imply the mm is
> going away (clone allows CLONE_VM without CLONE_SIGNAL - i.e. mm could
> be shared outside of thread group).

The main reason I'm OK with just updating the sched_process_exit()
tracepoint is because it is in an arbitrary location. The process is
exiting, but because the tracepoint is basically in the middle of the
routine, it doesn't really give us any information about the actual exit.

This tracepoint does give us if a task is exiting from an mm. You are
correct, it doesn't tell us if the mm is going away. If that is the
purpose, then here should be a tracepoint in the exit_mm() code or perhaps
even in the mput() function.

-- Steve