linux-kernel - Re: [PATCH v3 2/6] exit: hoist get_pid() in release_task() outside of tasklist

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Message-Id: <20250203175128.80319b42c9739f0d420080a4@linux-foundation.org>
Date: Mon, 3 Feb 2025 17:51:28 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>, ebiederm@...ssion.com,
 oleg@...hat.com, brauner@...nel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/6] exit: hoist get_pid() in release_task() outside
 of tasklist_lock

On Mon, 3 Feb 2025 21:22:31 +0100 Mateusz Guzik <mjguzik@...il.com> wrote:

> On Mon, Feb 3, 2025 at 9:14 PM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
> >
> > * Mateusz Guzik <mjguzik@...il.com> [250203 14:36]:
> > > On Mon, Feb 3, 2025 at 8:27 PM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
> > > >
> > > > * Mateusz Guzik <mjguzik@...il.com> [250201 11:31]:
> > > > > Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
> > > >
> > > > Change log is a bit sparse?  I get that the subject spells out what is
> > > > done, but anything to say here at all?  Reduces lock contention by
> > > > reducing lock time or something?  Maybe even some numbers you have in
> > > > the cover letter?
> > > >
> > >
> > > I did not measure this bit *specifically*.
> > >
> > > As one can expect get_pid issues an atomic and that's slow. And since
> > > it can happen *prior* to taking the global lock it seems like an
> > > obvious little nit to sort out.
> > >
> > > I would argue the change is self-explanatory given the cover-letter.
> >
> > But when you git blame on the file, you will not see that cover letter.
> 
> if this lands, I presume it is going to go through Andrew who uses
> tooling pulling in the cover letter for each commit

No, I copy the [0/n] description into the [1/n] changelog only.

> but i'm not going to argue this bit, just provide with a commit
> message which you think works and I'll use it

It's rather irregular to ask Liam to explain your patch!

The Subject: describes what the patch does (which was obvious from the
code anyway) but the changelog fails to explain *why* the change was
made.  You've explained "why" adequately within this discussion so I
suggest you condense those words into this patch's changelog.

General muse: if a reviewer asks questions regarding a patch then we
should treat those questions as bug reports against the changelogs and
code comments: required information is missing.  So please let's go
through reviewer questions as we prepare the next revision of a
patchset and make sure that all those questions are fully answered,