From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave McCracken <dcm@mccr.org>
Subject: Re: Re: [PATCH] Add hypercall to mark superpages to
	improve performance
Date: Sun, 2 May 2010 20:55:32 -0500
Message-ID: <201005022055.32509.dcm@mccr.org>
References: <C80360DB.11A0B%keir.fraser@eu.citrix.com>
Mime-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <C80360DB.11A0B%keir.fraser@eu.citrix.com>
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, Xen Developers List <xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

On Sunday 02 May 2010, Keir Fraser wrote:
> Oh, now I think about it, although your suggestion deals with type
> conflicts, it doesn't handle page lifetimes. What if a page is only mapped
> as a superpage? The page->count_info would not be incremented by the
> superpage mappings, and the page would be erroneously freed to the Xen free
> pools? So I'm not so sure we can so easily avoid the
> mess-with-every-page's-refcount on first mapping of a superpage... :-(

It should be simple enough to also check superpage->count_info in those 
places.  So the total mappings of a page would be page->count_info + 
superpage->count_info.  Good thing you suggested we also have a count in the 
superpage_info struct :)

Dave