linux-kernel - Re: [PATCH 03/13] MM: reclaim mustn't enter FS for swap-over-NFS

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Date:   Tue, 16 Nov 2021 00:32:51 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     NeilBrown <neilb@...e.de>
Cc:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Chuck Lever <chuck.lever@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/13] MM: reclaim mustn't enter FS for swap-over-NFS

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.