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Date: Thu, 7 Oct 2010 12:47:06 +0900
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
To: balbir@linux.vnet.ibm.com
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        containers@lists.linux-foundation.org,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Subject: Re: [RFC] Restrict size of page_cgroup->flags
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On Thu, 7 Oct 2010 08:44:59 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> * nishimura@mxp.nes.nec.co.jp <nishimura@mxp.nes.nec.co.jp> [2010-10-07 09:54:58]:
> 
> > On Wed, 6 Oct 2010 19:53:14 +0530
> > Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> > 
> > > I propose restricting page_cgroup.flags to 16 bits. The patch for the
> > > same is below. Comments?
> > > 
> > > 
> > > Restrict the bits usage in page_cgroup.flags
> > > 
> > > From: Balbir Singh <balbir@linux.vnet.ibm.com>
> > > 
> > > Restricting the flags helps control growth of the flags unbound.
> > > Restriciting it to 16 bits gives us the possibility of merging
> > > cgroup id with flags (atomicity permitting) and saving a whole
> > > long word in page_cgroup
> > > 
> > I agree that reducing the size of page_cgroup would be good and important.
> > But, wouldn't it be better to remove ->page, if possible ?
> >
> 
> Without the page pointer, how do we go from pc to page for reclaim? 
> 
We store page_cgroups in arrays now, so I suppose we can implement pc_to_pfn()
using the similar calculation as page_to_pfn() does.
IIRC, KAMEZAWA-san talked about it in another thread.

Thanks,
Daisuke Nishimura.