This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


RE: [Xen-devel] Shadow Page Tables in Xen

To: Gianluca Guida <glguida@xxxxxxxxx>, priya sehgal <priyagps@xxxxxxxxxxx>
Subject: RE: [Xen-devel] Shadow Page Tables in Xen
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>
Date: Tue, 21 Apr 2009 20:26:31 +0100
Accept-language: en-US
Acceptlanguage: en-US
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, Gianluca Guida <Gianluca.Guida@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>
Delivery-date: Tue, 21 Apr 2009 12:27:02 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <f8877f640904210759g53961640t6fd5ef12254b5dfc@xxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <46562.49315.qm@xxxxxxxxxxxxxxxxxxxxxxxxx> <f8877f640904210759g53961640t6fd5ef12254b5dfc@xxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcnCkdWTbkj2QusoR3my//pE3inMowAJNSpw
Thread-topic: [Xen-devel] Shadow Page Tables in Xen
> Have you actually measured this? I think that the major cause of page
> faults and VM slowdown is -- rather than page faults on write access
> -- the fact that we blow the shadow pagetables away everytime we clean
> the dirty bitmap, and this requires a long operation to remove from
> top to bottom all reference counts and reconstructing later the shadow
> pagetables on the next memory accesses.

Yep, ideally we'd just walking all the shadow leaf PTE's to just remove write 
access. I'd guess that this would be a much more worthwhile optimization than 
trying to 'pre-fetch' write faults.


Xen-devel mailing list