From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH RESEND 3/3 cgroup/for-5.20] cgroup: Make !percpu
 threadgroup_rwsem operations optional
Date: Tue, 26 Jul 2022 07:33:22 -1000
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To: Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny-IBi9RG/b67k@public.gmane.org>
Cc: Christian Brauner <brauner-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, John Stultz <john.stultz-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Dmitry Shmidt <dimitrysh-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

Hello,

On Tue, Jul 26, 2022 at 04:32:57PM +0200, Michal Koutn=FD wrote:
> On Sat, Jul 23, 2022 at 04:28:28AM -1000, Tejun Heo <tj-DgEjT+Ai2ygdnm+yR=
OfE0A@public.gmane.org> wrote:
> > This makes the hotter paths - fork and exit - slower as they're always
> > forced into the slow path. There is no reason to force this on everyone
> > especially given that more common static usage pattern can now complete=
ly
> > avoid write-locking the rwsem. Write-locking is elided when turning on =
and
> > off controllers on empty sub-trees and CLONE_INTO_CGROUP enables seedin=
g a
> > cgroup without grabbing the rwsem.
>=20
> Just a practical note that CLONE_INTO_CGROUP may not be so widespread
> yet [1][2].
> But generally, the change makes sense to me.

Yeah, I was disappoinetd that it wasn't being used by systemd already. It'd
be great if the glibc situation can be rectified soon because this is a much
better interface.

> > +	CGRP_ROOT_FAVOR_DYNMODS =3D (1 << 4),
> > +
> > +	/*
> >  	 * Enable cpuset controller in v1 cgroup to use v2 behavior.
> >  	 */
> > -	CGRP_ROOT_CPUSET_V2_MODE =3D (1 << 4),
> > +	CGRP_ROOT_CPUSET_V2_MODE =3D (1 << 16),
> > =20
> >  	/*
> >  	 * Enable legacy local memory.events.
> >  	 */
> > -	CGRP_ROOT_MEMORY_LOCAL_EVENTS =3D (1 << 5),
> > +	CGRP_ROOT_MEMORY_LOCAL_EVENTS =3D (1 << 17),
> > =20
> >  	/*
> >  	 * Enable recursive subtree protection
> >  	 */
> > -	CGRP_ROOT_MEMORY_RECURSIVE_PROT =3D (1 << 6),
> > +	CGRP_ROOT_MEMORY_RECURSIVE_PROT =3D (1 << 18),
>=20
> Why this new gap in flag bits?

To distinguish core and per-controller flags.

Thanks.

--=20
tejun