Date:   Tue, 16 Nov 2021 00:32:51 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     NeilBrown <neilb@suse.de>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Chuck Lever <chuck.lever@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, linux-nfs@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 03/13] MM: reclaim mustn't enter FS for swap-over-NFS
Message-ID: <YZNss/ujX3yovr/k@infradead.org>
References: <163702956672.25805.16457749992977493579.stgit@noble.brown>
 <163703064452.25805.16932817889703270242.stgit@noble.brown>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <163703064452.25805.16932817889703270242.stgit@noble.brown>
Precedence: bulk

On Tue, Nov 16, 2021 at 01:44:04PM +1100, NeilBrown wrote:
> +		/* ->flags can be updated non-atomicially (scan_swap_map_slots),
> +		 * but that will never affect SWP_FS_OPS, so the data_race
> +		 * is safe.
> +		 */
>  		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
> +			(PageSwapCache(page) &&
> +			 !data_race(page_swap_info(page)->flags & SWP_FS_OPS) &&
> +			 (sc->gfp_mask & __GFP_IO));

You might want to move the comment and SWP_FS_OPS into a little
inline helper.  That makes it a lot more readable and also avoids the
overly long line in the second hunk.