linux-kernel - Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use

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Message-ID: <20130821181733.GC3814@moon>
Date:	Wed, 21 Aug 2013 22:17:33 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	Jan Beulich <JBeulich@...e.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Xen-devel@...ts.xen.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with
 existing use

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.
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