From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mukesh Rathor Subject: Re: struct page_info Date: Fri, 24 Apr 2009 14:38:14 -0700 Message-ID: <49F23146.2060209@oracle.com> References: <49F12ECD.3040102@oracle.com> <49F17D61.76EA.0078.0@novell.com> Reply-To: mukesh.rathor@oracle.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <49F17D61.76EA.0078.0@novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: xen-devel List-Id: xen-devel@lists.xenproject.org Jan Beulich wrote: >>>> Mukesh Rathor 24.04.09 05:15 >>> >> Now, looking at it, the shadow page is confusing. >> >> /* Page is in use: ((count_info & PGC_count_mask) != 0). */ >> .. >> >> /* Page is in use as a shadow: count_info == 0. */ >> .. >> /* Page is on a free list: ((count_info & PGC_count_mask) == 0). */ >> .. >> >> If count_info == 0, and it implies shadow page, how's that different >>from an unallocated page which also would've count_info=0 I presume? > > These are not if-and-only-if conditions, so you can't conclude the use of > a page from just looking at count_info; only the other way around: from > e.g. knowing the page is in use as a shadow, you'll know count_info must > be zero. Ahh, so I found a mfn on the floor no easy way of knowing where it belongs. Okey. thanks Mukesh >> Also, if "Page is on a free list:", I assume one of the PGC_ fields would >> be set? > > Not would, but might. > > Jan