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

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Date:	Wed, 24 Jul 2013 22:52:35 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	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 07/24/2013 08:08 PM, Cyrill Gorcunov 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.
> 
> To resolve this we introduce _PTE_SWP_SOFT_DIRTY bit which is
> saved in pte entry for the page being swapped out. When such page
> is to be read back from a swap cache we check for bit presence
> and if it's there we clear it and restore the former _PAGE_SOFT_DIRTY
> bit back.
> 
> One of the problem was to find a place in pte entry where we can
> save the _PTE_SWP_SOFT_DIRTY bit while page is in swap. The
> _PAGE_PSE was chosen for that, it doesn't intersect with swap
> entry format stored in pte.
> 
> Reported-by: Andy Lutomirski <luto@...capital.net>
> Signed-off-by: Pavel Emelyanov <xemul@...allels.com>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Matt Mackall <mpm@...enic.com>
> Cc: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> Cc: Marcelo Tosatti <mtosatti@...hat.com>
> Cc: KOSAKI Motohiro <kosaki.motohiro@...il.com>
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>

Acked-by: Pavel Emelyanov <xemul@...allels.com>
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