Re: [PATCH] cgroup/cpuset: move PF_EXITING check before __GFP_HARDWALL in cpuset_current_node_allowed()

[Waiman Long <longman@redhat.com>]

On 5/7/26 8:33 AM, Michal Koutný wrote:
> On Thu, May 07, 2026 at 06:54:34PM +0800, Chen Wandun <chenwandun1@gmail.com> wrote:
>> This makes it unreachable in the common case, so dying tasks can get
>> stuck in direct reclaim or even trigger OOM while trying to exit,
>> despite being allowed to allocate from any node.
> (OTOH, the caused OOM could select this task and bypass the hardwall. So
> this should only expedite but no unblock the exit path.)
>
>> Move the PF_EXITING check before __GFP_HARDWALL so that dying tasks
>> can allocate memory from any node to exit quickly, even when cpusets
>> are enabled.
> This makes sense to me on its own (given other hardwall exemptions,
> namely the commit c596d9f320aaf ("cpusets: allow TIF_MEMDIE threads to
> allocate anywhere")).
>
> Acked-by: Michal Koutný <mkoutny@suse.com>

This looks good to me too.

Acked-by: Waiman Long <longman@redhat.com>

>
>
> At first, I wondered whether this could happen on cpuset v2 -- it can --
> because only per-cpuset hardwalling is absent but the generic logic for
> GFP_USER allocations is still meant to be in place. Nevertheless, it
> occured to me we can spare callback_lock in this function (a separate
> chaneg for cpuset_current_node_allowed()):
>
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -4213,6 +4213,9 @@ bool cpuset_current_node_allowed(int node, gfp_t gfp_mask)
>          if (current->flags & PF_EXITING) /* Let dying task have memory */
>                  return true;
>
> +       if (is_in_v2_mode())
> +               return true;
> +
>          /* Not hardwall and node outside mems_allowed: scan up cpusets */
>          spin_lock_irqsave(&callback_lock, flags);

Yes, it is a performance optimization that is worth to have as cgroup v2 
doesn't have the concept of memory hardwall yet.

Cheers,
Longman