Re: [PATCH RESEND] mm/vmalloc: Use dedicated unbound workqueues for vmap drain

[Uladzislau Rezki <urezki@gmail.com>]

On Sat, Sep 05, 2026 at 03:37:04PM -0700, Andrew Morton wrote:
> On Sat,  5 Sep 2026 17:27:17 +0200 "Uladzislau Rezki (Sony)" <urezki@gmail.com> wrote:
> 
> > drain_vmap_area_work() function can take >10ms to complete
> > when there are many accumulated vmap areas in a system with
> > high CPU count, causing workqueue watchdog warnings when run
> > via schedule_work():
> > 
> >   workqueue: drain_vmap_area_work hogged CPU for >10000us
> > 
> > Move the top-level drain work to a dedicated WQ_UNBOUND
> > workqueue so the scheduler can run this background work
> > on any available CPU, improving responsiveness. Use the
> > WQ_MEM_RECLAIM to ensure forward progress under memory
> > pressure.
> > 
> > Move purge helpers to separate WQ_UNBOUND | WQ_MEM_RECLAIM
> > workqueue. This allows drain_vmap_work to wait for helpers
> > completion without creating dependency on the same rescuer
> > thread and avoid a potential parent/child deadlock.
> > 
> > Simplify purge helper scheduling by removing cpumask-based
> > iteration to iterating directly over vmap nodes checking
> > work_queued state.
> 
> Thanks.
> 
> > Cc: stable@vger.kernel.org
> > Cc: Dev Jain <dev.jain@arm.com>
> > Cc: Ye Liu <ye.liu@linux.dev>
> > Cc: lirongqing <lirongqing@baidu.com>
> > Fixes: 72210662c5a2 ("mm: vmalloc: offload free_vmap_area_lock lock")
> > Link: https://lore.kernel.org/all/20260319074307.2325-1-lirongqing@baidu.com/
> > Reviewed-by: Baoquan He <bhe@redhat.com>
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> 
> I think what we wanted here was
> 
> Reported-by: Li RongQing <lirongqing@baidu.com>
> Closes: https://lore.kernel.org/all/20260319074307.2325-1-lirongqing@baidu.com/
> 
> so I made that change.
> 
Yep :) Thank you!

--
Uladzislau Rezki