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

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Message-ID: <ZAj+hMFcr4NeclZs@bombadil.infradead.org>
Date:   Wed, 8 Mar 2023 13:30:44 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     hughd@...gle.com, akpm@...ux-foundation.org, willy@...radead.org,
        brauner@...nel.org, linux-mm@...ck.org, p.raghav@...sung.com,
        da.gomez@...sung.com, a.manzanares@...sung.com, dave@...olabs.net,
        yosryahmed@...gle.com, keescook@...omium.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] shmem: move reclaim check early on writepages()

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@...hat.com>

Great thanks,

  Luis