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Date: Thu, 17 Apr 2008 20:22:21 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: LKML <linux-kernel@vger.kernel.org>, shiwh@cn.fujitsu.com,
       "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>,
       "xemul@openvz.org" <xemul@openvz.org>
Subject: Re: [PATCH] fix page_reset_bad_cgroup
Message-Id: <20080417202221.063aa171.akpm@linux-foundation.org>
In-Reply-To: <20080418121046.892c44a5.kamezawa.hiroyu@jp.fujitsu.com>
References: <20080418121046.892c44a5.kamezawa.hiroyu@jp.fujitsu.com>
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On Fri, 18 Apr 2008 12:10:46 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> page->page_cgroup is unsigned long. Should be cleared by 0UL.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> 
> Index: linux-2.6.25/include/linux/memcontrol.h
> ===================================================================
> --- linux-2.6.25.orig/include/linux/memcontrol.h
> +++ linux-2.6.25/include/linux/memcontrol.h
> @@ -30,7 +30,7 @@ struct mm_struct;
>  extern void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p);
>  extern void mm_free_cgroup(struct mm_struct *mm);
>  
> -#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0)
> +#define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0UL)

That's pretty cosmetic.

In fact it could be argued that we shouldn't do this.  "0" is zero
regardless of the type of the LHS.  So if we later change page_cgroup to
u32 or u16 or `struct superblock *', the old page_reset_bad_cgroup() will
happily continue to work.  There's no need to make this code aware of
page_cgroup's type, to this extent?