linux-kernel - Re: [PATCH v4 5/5] pagemap: add mmap-exclusive bit for marking pages mapped only here

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Message-ID: <20150721081755.GD4490@hori1.linux.bs1.fc.nec.co.jp>
Date:	Tue, 21 Jul 2015 08:17:56 +0000
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Mark Williamson <mwilliamson@...o-software.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v4 5/5] pagemap: add mmap-exclusive bit for marking
 pages mapped only here

On Tue, Jul 14, 2015 at 06:37:49PM +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)
> 
> CoWed pages in (MAP_FILE | MAP_PRIVATE) areas are anon in this context.
> 
> MMap-exclusive bit doesn't reflect potential page-sharing via swapcache:
> page could be mapped once but has several swap-ptes which point to it.
> Application could detect that by swap bit in pagemap entry and touch
> that pte via /proc/pid/mem to get real information.
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Requested-by: Mark Williamson <mwilliamson@...o-software.com>
> Link: http://lkml.kernel.org/r/CAEVpBa+_RyACkhODZrRvQLs80iy0sqpdrd0AaP_-tgnX3Y9yNQ@mail.gmail.com

Reviewed-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>--
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