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

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Date:   Tue, 25 Jan 2022 16:50:14 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH v2 1/1] mm/vmalloc: Move draining areas out of caller
 context

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.