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Date: Wed, 19 Jan 2011 10:11:12 +0900
From: nishimura@mxp.nes.nec.co.jp
Subject: Re: [PATCH v4] mm: add replace_page_cache_page() function
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
cc: Andrew Morton <akpm@linux-foundation.org>,
        Miklos Szeredi <miklos@szeredi.hu>, minchan.kim@gmail.com,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
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> On Wed, 19 Jan 2011 09:27:33 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> 
>> On Tue, 18 Jan 2011 15:28:44 -0800
>> Andrew Morton <akpm@linux-foundation.org> wrote:
>> 
>> > On Tue, 18 Jan 2011 12:18:11 +0100
>> > Miklos Szeredi <miklos@szeredi.hu> wrote:
>> > 
>> > > +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
>> > > +{
>> > > +	int error;
>> > > +	struct mem_cgroup *memcg = NULL;
>> > 
>> > I'm suspecting that the unneeded initialisation was added to suppress a
>> > warning?
>> > 
>> No.
>> It's necessary for mem_cgroup_{prepare|end}_migration().
>> mem_cgroup_prepare_migration() will return without doing anything in
>> "if (mem_cgroup_disabled()" case(iow, "memcg" is not overwritten),
>> but mem_cgroup_end_migration() depends on the value of "memcg" to decide
>> whether prepare_migration has succeeded or not.
>> This may not be a good implementation, but IMHO I'd like to to initialize
>> valuable before using it in general.
>> 
> 
> I think it can be initlized in mem_cgroup_prepare_migration().
> I'll send patch later.
> 
I see, thanks.

I think you know it, but just a note:
mem_cgroup_{try_charge|commit_charge}_swapin()
use the same logic, so try_charge_swapin() should also be changed
for consistency.

Thanks,
Daisuke Nishimura.