linux-kernel - Re: [PATCH v2 1/3] pagemap: add mmap-exclusive bit for marking pages mapped only here

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Message-ID: <20150512104055.GB18365@node.dhcp.inet.fi>
Date:	Tue, 12 May 2015 13:40:55 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:	linux-mm@...ck.org, Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mark Williamson <mwilliamson@...o-software.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	linux-api@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
	Vlastimil Babka <vbabka@...e.cz>, Pavel Machek <pavel@....cz>,
	Mark Seaborn <mseaborn@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel James <djames@...o-software.com>,
	Finn Grimwood <fgrimwood@...o-software.com>
Subject: Re: [PATCH v2 1/3] pagemap: add mmap-exclusive bit for marking pages
 mapped only here

On Tue, May 12, 2015 at 12:43:03PM +0300, Konstantin Khlebnikov wrote:
> This patch sets bit 56 in pagemap if this page is mapped only once.
> It allows to detect exclusively used pages without exposing PFN:
> 
> present file exclusive state
> 0       0    0         non-present
> 1       1    0         file page mapped somewhere else
> 1       1    1         file page mapped only here
> 1       0    0         anon non-CoWed page (shared with parent/child)
> 1       0    1         anon CoWed page (or never forked)

Probably, worth noting that file-private pages are anon in this context.

-- 
 Kirill A. Shutemov
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