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

[Hillf Danton]

On Sat, 5 Sep 2026 17:27:17 +0200 "Uladzislau Rezki (Sony)" 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.
>
If the dedicated worker will run for 4ms on CPU2 before the tick irq kicks it
off cpu, the system event worker on CPU2 has to wait at least for 4ms to handle
200 events for example in 1ms, the net effect is the same as the current scenario
where 200 events wait for the drain_vmap_area_work to complete on CPU1.

Different workers does not help to dramatically decrement the micro seconds
the drain_vmap_area_work takes.