linux-kernel - Re: [PATCH v2] cgroup/cpuset-v1: Add missing support for cpuset_v2

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Message-ID: <CABdmKX2zmQT=ZvRAHOjfxg9hgJ_9iCpQj_SDytHVG2UobdsfMw@mail.gmail.com>
Date: Wed, 16 Apr 2025 10:55:22 -0700
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Kamalesh Babulal <kamalesh.babulal@...cle.com>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Koutný <mkoutny@...e.com>, 
	Waiman Long <longman@...hat.com>, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cgroup/cpuset-v1: Add missing support for cpuset_v2_mode

On Wed, Apr 16, 2025 at 2:19 AM Kamalesh Babulal
<kamalesh.babulal@...cle.com> wrote:
>
> Hi,
>
> On 4/16/25 5:23 AM, T.J. Mercier wrote:
> > Android has mounted the v1 cpuset controller using filesystem type
> > "cpuset" (not "cgroup") since 2015 [1], and depends on the resulting
> > behavior where the controller name is not added as a prefix for cgroupfs
> > files. [2]
> >
> > Later, a problem was discovered where cpu hotplug onlining did not
> > affect the cpuset/cpus files, which Android carried an out-of-tree patch
> > to address for a while. An attempt was made to upstream this patch, but
> > the recommendation was to use the "cpuset_v2_mode" mount option
> > instead. [3]
> >
> > An effort was made to do so, but this fails with "cgroup: Unknown
> > parameter 'cpuset_v2_mode'" because commit e1cba4b85daa ("cgroup: Add
> > mount flag to enable cpuset to use v2 behavior in v1 cgroup") did not
> > update the special cased cpuset_mount(), and only the cgroup (v1)
> > filesystem type was updated.
> >
> > Add parameter parsing to the cpuset filesystem type so that
> > cpuset_v2_mode works like the cgroup filesystem type:
> >
> > $ mkdir /dev/cpuset
> > $ mount -t cpuset -ocpuset_v2_mode none /dev/cpuset
> > $ mount|grep cpuset
> > none on /dev/cpuset type cgroup (rw,relatime,cpuset,noprefix,cpuset_v2_mode,release_agent=/sbin/cpuset_release_agent)
> >
> > [1] https://cs.android.com/android/_/android/platform/system/core/+/b769c8d24fd7be96f8968aa4c80b669525b930d3
> > [2] https://cs.android.com/android/platform/superproject/main/+/main:system/core/libprocessgroup/setup/cgroup_map_write.cpp;drc=2dac5d89a0f024a2d0cc46a80ba4ee13472f1681;l=192
> > [3] https://lore.kernel.org/lkml/f795f8be-a184-408a-0b5a-553d26061385@redhat.com/T/
> >
> > Fixes: e1cba4b85daa ("cgroup: Add mount flag to enable cpuset to use v2 behavior in v1 cgroup")
> > Signed-off-by: T.J. Mercier <tjmercier@...gle.com>
>
> The patch looks good to me, please feel free to add
>
> Reviewed-by: Kamalesh Babulal <kamalesh.babulal@...cle.com>
>
> One nit below:
>
> > ---
> >  kernel/cgroup/cgroup.c | 29 +++++++++++++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> >
> > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> > index 27f08aa17b56..cf30ff2e7d60 100644
> > --- a/kernel/cgroup/cgroup.c
> > +++ b/kernel/cgroup/cgroup.c
> > @@ -2353,9 +2353,37 @@ static struct file_system_type cgroup2_fs_type = {
> >  };
> >
> >  #ifdef CONFIG_CPUSETS_V1
> > +enum cpuset_param {
> > +     Opt_cpuset_v2_mode,
> > +};
> > +
> > +const struct fs_parameter_spec cpuset_fs_parameters[] = {
> > +     fsparam_flag  ("cpuset_v2_mode", Opt_cpuset_v2_mode),
> > +     {}
> > +};
>
> A minor optimization you may want to convert the cpuset_fs_parameters into
> a static const.

Thanks, I copied from cgroup1_fs_parameters since that's where
cpuset_v2_mode lives, which doesn't have the static currently
(cgroup2_fs_parameters does). Let me update cpuset_fs_parameters in
v3, and add a second patch for cgroup1_fs_parameters.

> --
> Cheers,
> Kamalesh
>