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Date: Wed, 13 Jul 2011 16:11:21 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Hugh Dickins <hughd@google.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/12] mm: let swap use exceptional entries
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On Tue, 12 Jul 2011 15:08:58 -0700 (PDT)
Hugh Dickins <hughd@google.com> wrote:

> > 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?
> 
> The naming was intentionally bland, because other filesystems might
> in future have other uses for such exceptional entries.
> 
> (I think the field size would generally defeat it, but you can,
> for example, imagine a small filesystem wanting to save sector number
> there when a page is evicted.)
> 
> But let's go bland when it's more familiar, and such uses materialize -
> particularly since I only placed those checks in places where they're
> needed now for shmem/tmpfs/swap.
> 
> I'll keep the bland naming, if that's okay, but send a patch adding
> a line of comment in such places.  Mentioning shmem, tmpfs, swap.

A better fix would be to create a nicely-documented filemap-specific
function with a non-bland name which simply wraps
radix_tree_exception().