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

From: Pavel Emelyanov
Date: Wed Jul 24 2013 - 14:52:50 EST

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@xxxxxxxxxxxxxx>
> Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Matt Mackall <mpm@xxxxxxxxxxx>
> Cc: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx>
> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>

Acked-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
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