linux-kernel - Re: [PATCH v3] exit: move trace_sched_process_exit earlier in do

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Date: Tue, 19 Mar 2024 14:57:18 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: wenyang.linux@...mail.com
Cc: Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.org>,
 Oleg Nesterov <oleg@...hat.com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Masami Hiramatsu <mhiramat@...nel.org>,
 Christian Brauner <brauner@...nel.org>, Mel Gorman
 <mgorman@...hsingularity.net>, Peter Zijlstra <peterz@...radead.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] exit: move trace_sched_process_exit earlier in
 do_exit()

On Sun, 10 Mar 2024 13:25:29 +0800 wenyang.linux@...mail.com wrote:

> From: Wen Yang <wenyang.linux@...mail.com>
> 
> Currently coredump_task_exit() takes some time to wait for the generation
> of the dump file. But if the user-space wants to receive a notification
> as soon as possible it maybe inconvenient.

If userspace is awaiting this notification to say "it's now OK to read
the dump file" then it could break things?

> Move trace_sched_process_exit() earlier in do_exit().
> This way a user-space monitor could detect the exits and
> potentially make some preparations in advance.
> 
> Oleg initially proposed this suggestion, and Steven further provided some
> detailed suggestions, and Mathieu carefully checked the historical code
> and said:
> : I've checked with Matthew Khouzam (maintainer of Trace Compass)
> : which care about this tracepoint, and we have not identified any
> : significant impact of moving it on its model of the scheduler, other
> : than slightly changing its timing.
> : I've also checked quickly in lttng-analyses and have not found
> : any code that care about its specific placement.
> : So I would say go ahead and move it earlier in do_exit(), it's
> : fine by me.

I'm not seeing a clear need for this change.  "maybe inconveniant" is
quite thin.  Please fully describe what motivated you to work on this?