mm/vmalloc: use dedicated unbound workqueues for vmap drain

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.

Link: https://lore.kernel.org/20260905152717.11711-1-urezki@gmail.com
Fixes: 72210662c5a2 ("mm: vmalloc: offload free_vmap_area_lock lock")
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Li RongQing <lirongqing@baidu.com>
Closes: https://lore.kernel.org/all/20260319074307.2325-1-lirongqing@baidu.com/
Reviewed-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Ye Liu <liuye@kylinos.cn>
Cc: Dev Jain <dev.jain@arm.com>
Cc: <stable@vger.kernel.org>

0 files changed, 0 insertions, 0 deletions