[RFC] Restrict size of page_cgroup->flags

Balbir Singh balbir at linux.vnet.ibm.com
Wed Oct 6 21:08:02 PDT 2010


* nishimura at mxp.nes.nec.co.jp <nishimura at mxp.nes.nec.co.jp> [2010-10-07 12:47:06]:

> On Thu, 7 Oct 2010 08:44:59 +0530
> Balbir Singh <balbir at linux.vnet.ibm.com> wrote:
> 
> > * nishimura at mxp.nes.nec.co.jp <nishimura at mxp.nes.nec.co.jp> [2010-10-07 09:54:58]:
> > 
> > > On Wed, 6 Oct 2010 19:53:14 +0530
> > > Balbir Singh <balbir at 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 at 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.
>

Yes, correct we do. Your suggestions, IIUC is to reuse part of the
flags to store the section number where the pc belongs and then use
that to remove ->page pointer.

-- 
	Three Cheers,
	Balbir


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