linux-kernel - Re: [PATCH 2/12] mm: let swap use exceptional entries

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Message-Id: <20110618145254.1b333344.akpm@linux-foundation.org>
Date:	Sat, 18 Jun 2011 14:52:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/12] mm: let swap use exceptional entries

On Tue, 14 Jun 2011 03:43:47 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:

> --- linux.orig/mm/filemap.c	2011-06-13 13:26:44.430284135 -0700
> +++ linux/mm/filemap.c	2011-06-13 13:27:34.526532556 -0700
> @@ -717,9 +717,12 @@ repeat:
>  		page = radix_tree_deref_slot(pagep);
>  		if (unlikely(!page))
>  			goto out;
> -		if (radix_tree_deref_retry(page))
> +		if (radix_tree_exception(page)) {
> +			if (radix_tree_exceptional_entry(page))
> +				goto out;
> +			/* radix_tree_deref_retry(page) */
>  			goto repeat;
> -
> +		}
>  		if (!page_cache_get_speculative(page))
>  			goto repeat;

All the crap^Wnice changes made to filemap.c really need some comments,
please.  Particularly when they're keyed off the bland-sounding
"radix_tree_exception()".  Apparently they have something to do with
swap, but how is the poor reader to know this?

Also, commenting out a function call might be meaningful information for
Hugh-right-now, but for other people later on, they're just a big WTF.

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