Re: [PATCH v2 1/1] mm/vmalloc: Move draining areas out of caller context

[Matthew Wilcox]

On Tue, Jan 25, 2022 at 05:39:12PM +0100, Uladzislau Rezki (Sony) wrote:
> @@ -1768,7 +1776,8 @@ static void free_vmap_area_noflush(struct vmap_area *va)
>  
>  	/* After this point, we may free va at any time */
>  	if (unlikely(nr_lazy > lazy_max_pages()))
> -		try_purge_vmap_area_lazy();
> +		if (!atomic_xchg(&drain_vmap_work_in_progress, 1))
> +			schedule_work(&drain_vmap_work);
>  }

Is it necessary to have drain_vmap_work_in_progress?  The documentation
says:

 * This puts a job in the kernel-global workqueue if it was not already
 * queued and leaves it in the same position on the kernel-global
 * workqueue otherwise.

and the implementation seems to use test_and_set_bit() to ensure this
is true.