linux-kernel - Re: [PATCH] mm: Save soft-dirty bits on swapped pages

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Message-ID: <20130724163734.GE24851@moon>
Date:	Wed, 24 Jul 2013 20:37:34 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH] mm: Save soft-dirty bits on swapped pages

On Wed, Jul 24, 2013 at 09:23:14AM -0700, Andy Lutomirski wrote:
> On Wed, Jul 24, 2013 at 9:08 AM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> > Andy Lutomirski reported that in case if a page with _PAGE_SOFT_DIRTY
> > bit set get swapped out, the bit is getting lost and no longer
> > available when pte read back.
> 
> Potentially silly question (due to my completely lack of understanding
> of how swapping works in Linux): what about file-backed pages?
> (Arguably these would be best supported by filesystems instead of by
> the core vm, in which case it might make sense to drop soft-dirty
> support for these pages entirely.)

Hi Andy, if I understand you correctly "file-backed pages" are carried
in pte with _PAGE_FILE bit set and the swap soft-dirty bit won't be
used on them but _PAGE_SOFT_DIRTY will be set on write if only I've
not missed something obvious (Pavel?).
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