From: Andrew Morton <akpm@linux-foundation.org>
To: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
minchan.kim@gmail.com, kamezawa.hiroyu@jp.fujitsu.com,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] mm: add replace_page_cache_page() function
Date: Tue, 18 Jan 2011 16:41:33 -0800 [thread overview]
Message-ID: <20110118164133.9fecc2c6.akpm@linux-foundation.org> (raw)
In-Reply-To: <20110119092733.4927f935.nishimura@mxp.nes.nec.co.jp>
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,
It's a *surprising* implementation, in the context of kernel
conventions. At least, it fooled me :)
Which makes it a not-good implementation, really. Also, it's
undocumented.
> but IMHO I'd like to to initialize
> valuable before using it in general.
mem_cgroup_prepare_migration() performs the initialisation! We do this
in many places - it's the basic "function with more than one return
value" mechanism.
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next prev parent reply other threads:[~2011-01-19 0:41 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-18 11:18 [PATCH v4] mm: add replace_page_cache_page() function Miklos Szeredi
2011-01-18 23:28 ` Andrew Morton
2011-01-19 0:27 ` Daisuke Nishimura
2011-01-19 0:41 ` Andrew Morton [this message]
2011-01-19 0:48 ` KAMEZAWA Hiroyuki
2011-01-19 1:11 ` nishimura
2011-01-19 1:23 ` KAMEZAWA Hiroyuki
2011-01-21 5:52 ` Daisuke Nishimura
2011-01-21 6:17 ` KAMEZAWA Hiroyuki
2011-01-19 0:33 ` KAMEZAWA Hiroyuki
2011-01-19 1:24 ` Minchan Kim
2011-01-19 1:48 ` Andrew Morton
2011-01-19 2:17 ` Minchan Kim
2011-09-08 23:52 ` Andrew Morton
2011-09-09 1:43 ` KAMEZAWA Hiroyuki
2011-01-19 1:17 ` Minchan Kim
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