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

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Message-ID: <nkwn5nap777ebra37cubkxwqitrcx6ykjflz7gixmsvls3risn@4ss5ogyupi3o>
Date: Mon, 3 Feb 2025 15:28:24 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: ebiederm@...ssion.com, oleg@...hat.com, brauner@...nel.org,
        akpm@...ux-foundation.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

* Mateusz Guzik <mjguzik@...il.com> [250203 15:22]:
> 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
> 
> but i'm not going to argue this bit, just provide with a commit
> message which you think works and I'll use it

Your comment above states why this is beneficial.  Why not use a
variation of your statement of get_pid issuing an atomic which can be
removed from the locking area?  This seems like an important detail to
capture.

> 
> -- 
> Mateusz Guzik <mjguzik gmail.com>