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Subject: Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Wed, 21 Aug 2013 20:50:26 +0200
To: Cyrill Gorcunov <gorcunov@gmail.com>,
        David Vrabel <david.vrabel@citrix.com>
CC: Jan Beulich <JBeulich@suse.com>, Andy Lutomirski <luto@amacapital.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Xen-devel@lists.xen.org, Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Pavel Emelyanov <xemul@parallels.com>, Ingo Molnar <mingo@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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But is there a manifest bug or not?  What is the deal with Xen?

Cyrill Gorcunov <gorcunov@gmail.com> wrote:
>On Wed, Aug 21, 2013 at 09:25:47PM +0400, Cyrill Gorcunov wrote:
>> > 
>> > However, I do find the use of PTE bits in this way somewhat
>fragile.
>> > What other potential corner cases might still remain that will
>require
>> > further games with PTE bits?
>> 
>>   OK, so this is not a bug finally. The problem is that 2 level pte
>is
>> quite small and 7th bit is the only one spare I can use for soft
>dirty
>> tracking when page get swapped out. And swap engine is very depending
>> on pte being non-present, so we are on a safe side.
>
>To make it clear: I'm working on patch that won't use pse bit for dirty
>page tracking, just give some time to cook it and test.

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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