linux-kernel - Re: [patch 1/2] [PATCH] mm: Save soft-dirty bits on swapped pages

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Date:	Wed, 31 Jul 2013 12:16:12 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>, <akpm@...ux-foundation.org>
CC:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<luto@...capital.net>, <gorcunov@...nvz.org>, <mpm@...enic.com>,
	<xiaoguangrong@...ux.vnet.ibm.com>, <mtosatti@...hat.com>,
	<kosaki.motohiro@...il.com>, <sfr@...b.auug.org.au>,
	<peterz@...radead.org>, <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [patch 1/2] [PATCH] mm: Save soft-dirty bits on swapped pages

On 07/31/2013 12:41 AM, 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: Cyrill Gorcunov <gorcunov@...nvz.org>

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

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