Re: [PATCH 3/6] shmem: move reclaim check early on writepages()

From: Luis Chamberlain <mcgrof@kernel.org>
To: David Hildenbrand <david@redhat.com>
Cc: hughd@google.com, akpm@linux-foundation.org, willy@infradead.org,
	brauner@kernel.org, linux-mm@kvack.org, p.raghav@samsung.com,
	da.gomez@samsung.com, a.manzanares@samsung.com,
	dave@stgolabs.net, yosryahmed@google.com, keescook@chromium.org,
	patches@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/6] shmem: move reclaim check early on writepages()
Date: Wed, 8 Mar 2023 13:30:44 -0800	[thread overview]
Message-ID: <ZAj+hMFcr4NeclZs@bombadil.infradead.org> (raw)
In-Reply-To: <2a3386e7-9b09-f22e-ee39-a37a046d54ec@redhat.com>

On Mon, Mar 06, 2023 at 03:01:52PM +0100, David Hildenbrand wrote:
> On 03.03.23 00:27, Luis Chamberlain wrote:
> > @@ -1340,6 +1340,18 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
> >   	swp_entry_t swap;
> >   	pgoff_t index;
> > +	/*
> > +	 * Our capabilities prevent regular writeback or sync from ever calling
> > +	 * shmem_writepage; but a stacking filesystem might use ->writepage of
> > +	 * its underlying filesystem, in which case tmpfs should write out to
> > +	 * swap only in response to memory pressure, and not for the writeback
> > +	 * threads or sync.
> > +	 */
> > +	if (!wbc->for_reclaim) {
> 
> if (WARN_ON_ONCE(!wbc->for_reclaim))
> 
> > +		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */
> 
> And drop the comment :) That's what WARN_ON_ONCE is all about.

Good call, will add that to v2.

> Acked-by: David Hildenbrand <david@redhat.com>

Great thanks,

  Luis