linux-kernel - Re: [PATCH 6/6] memcg: make mem_cgroup_page

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Message-ID: <20101112082921.GH9131@cmpxchg.org>
Date:	Fri, 12 Nov 2010 09:29:21 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Minchan Kim <minchan.kim@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] memcg: make mem_cgroup_page_stat() return value
 unsigned

On Tue, Nov 09, 2010 at 01:24:31AM -0800, Greg Thelen wrote:
> mem_cgroup_page_stat() used to return a negative page count
> value to indicate value.

Whoops :)

> mem_cgroup_page_stat() has changed so it never returns
> error so convert the return value to the traditional page
> count type (unsigned long).

This changelog feels a bit beside the point.

What's really interesting is that we now don't consider negative sums
to be invalid anymore, but just assume zero!  There is a real
semantical change here.

That the return type can then be changed to unsigned long is a nice
follow-up cleanup that happens to be folded into this patch.
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