linux-kernel - RE: [RFC V2] mm:add zero_page _mapcount when mapped into user space

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Date:	Fri, 5 Dec 2014 16:08:42 +0800
From:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>
To:	'Konstantin Khlebnikov' <koct9i@...il.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [RFC V2] mm:add zero_page _mapcount when mapped into user space

> -----Original Message-----
> From: Konstantin Khlebnikov [mailto:koct9i@...il.com]
> Sent: Friday, December 05, 2014 2:39 PM
> To: Kirill A. Shutemov
> Cc: Wang, Yalin; linux-kernel@...r.kernel.org; linux-mm@...ck.org; linux-
> arm-kernel@...ts.infradead.org
> Subject: Re: [RFC V2] mm:add zero_page _mapcount when mapped into user
> space
> 
> On Thu, Dec 4, 2014 at 3:28 PM, Kirill A. Shutemov <kirill@...temov.name>
> wrote:
> > On Thu, Dec 04, 2014 at 02:10:53PM +0800, Wang, Yalin wrote:
> >> > -----Original Message-----
> >> > From: Kirill A. Shutemov [mailto:kirill@...temov.name]
> >> > Sent: Tuesday, December 02, 2014 7:30 PM
> >> > To: Wang, Yalin
> >> > Cc: 'linux-kernel@...r.kernel.org'; 'linux-mm@...ck.org';
> >> > 'linux-arm- kernel@...ts.infradead.org'
> >> > Subject: Re: [RFC V2] mm:add zero_page _mapcount when mapped into
> >> > user space
> >> >
> >> > On Tue, Dec 02, 2014 at 05:27:36PM +0800, Wang, Yalin wrote:
> >> > > This patch add/dec zero_page's _mapcount to make sure the
> >> > > mapcount is correct for zero_page, so that when read from
> >> > > /proc/kpagecount, zero_page's mapcount is also correct, userspace
> >> > > process like procrank can calculate PSS correctly.
> 
> Instead of tweaking mapcount you could mark zero-pages in /proc/kpageflags
> and handle them accordingly in userspace. Or mark zero pages with special
> magic _mapcount and detect it in /proc/kpagecount.
> 
I think add KPF_ZERO_PAGE in kpageflags is better.
I will make another patch for review .

Thanks