linux-kernel - Re: [PATCH] mm: migrate: One less atomic operation

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Message-Id: <20111108145706.11da104e.akpm@linux-foundation.org>
Date:	Tue, 8 Nov 2011 14:57:06 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jacobo Giralt <jacobo.giralt@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, mgorman@...e.de,
	minchan.kim@...il.com, hughd@...gle.com, hannes@...xchg.org,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [PATCH] mm: migrate: One less atomic operation

On Sat, 05 Nov 2011 15:38:17 +0100
Jacobo Giralt <jacobo.giralt@...il.com> wrote:

> >From 3754c8617ef4377ce2ca2e3b28bdc28f8de1aa0d Mon Sep 17 00:00:00 2001
> From: Jacobo Giralt <jacobo.giralt@...il.com>
> Date: Sat, 5 Nov 2011 13:12:50 +0100
> Subject: [PATCH] mm: migrate: One less atomic operation
> 
> migrate_page_move_mapping drops a reference from the
> old page after unfreezing its counter. Both operations
> can be merged into a single atomic operation by
> directly unfreezing to one less reference.
> 
> The same applies to migrate_huge_page_move_mapping.
> 

Fair enough.

urgh, you made me look at stuff :(

page_unfreeze_refs() and set_page_refcounted() are fishily similar.

page_unfreeze_refs() should use set_page_count().

set_page_count() is defined in the wrong file.

set_page_refcounted() should use page_count().

iow, a bit of a mess.
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