Re: [PATCH-next v3 3/5] cgroup/cpuset: Made cpuset_attach_old_cs track task group leaders

[Waiman Long]

On 5/28/26 10:19 PM, Guopeng Zhang wrote:
> 在 2026/5/27 23:37, Waiman Long 写道:
> > There are two possible ways that migration of tasks from multiple source
> > cpusets to a target cpuset can happen. Either a multithread application
> > with threads in different cpusets is wholely moved to a new cpuset
> > or disabling of v2 cpuset controller will move all the tasks in child
> > cpusets to the parent cpuset.
> >
> > In the former case, t is the mm setting of the group leader that really
> > matters. So cpuset_attach_old_cs should track the oldcs of the thread
> > leader. In the latter case, effective_mems of child cpusets must always
> > be a subset of the parent. So no real page migration will be necessary
> > no matter which child cpuset is selected as cpuset_attach_old_cs.
> >
> > IOW, cpuset_attach_old_cs should be updated to match the latest task
> > group leader in cpuset_can_attach().
> >
> > Suggested-by: Ridong Chen <ridong.chen@xxxxxxxxx>
> > Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> > ---
> >   kernel/cgroup/cpuset.c | 18 ++++++++++++++++++
> >   1 file changed, 18 insertions(+)
> >
> > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> > index 4457c4f11fce..b233a71f9b7c 100644
> > --- a/kernel/cgroup/cpuset.c
> > +++ b/kernel/cgroup/cpuset.c
> > @@ -2967,6 +2967,20 @@ static int update_prstate(struct cpuset *cs, int new_prs)
> >   /*
> >    * cpuset_can_attach() and cpuset_attach() specific internal data
> >    * Protected by cpuset_mutex
> > + *
> > + * The cpuset_attach_old_cs is used mainly by cpuset_migrate_mm() tp get the
> > + * old_mems_allowed value. There are two ways that many-to-one cpuset migration
> > + * can happen:
> Hi Waiman,
>
> I applied this series locally and ran some of my test cases. I didn't
> observe any issue so far.
>
> While doing a static/checkpatch pass, I noticed a few minor issues in
> patches 3, 4 and 5. They are all non-functional nits.
>
> For this patch, I only noticed a couple of small wording/typo nits in
> the new comment:
>
> s/tp get/to get/

Thanks for the review, will fix the typo in the next version.

Cheers,
Longman