From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: HVM and free_memory query Date: Fri, 10 Jul 2009 14:46:40 +0100 Message-ID: References: <4A5644C8.4040306@3tera.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4A5644C8.4040306@3tera.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: Apoorva Kulkarni , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 09/07/2009 20:28, "Apoorva Kulkarni" wrote: > #xm list > Name ID Mem VCPUs State > Time(s) > Domain-0 0 512 1 r----- 25251.4 > controller 1 512 1 -b---- 39948.6 > vm.windows03 44 30720 1 r----- 22.0 > > As you can see, the free_memory shown is 337M which is a good 241M less than > what it should have been (31298M - 30720M = 578M) after the Windows VM was > created. My question here is where/why does xen use that extra 241M. Any > pointers much appreciated. It's used for shadow pagetables and other memory book-keeping structures. This reservation is sized as a fraction of the domain's configured memory allocation -- the fraction is just under 0.8%. And 0.8% of 30720MB is 245MB, so that works out just about right. This is one of those cases where a small fraction of a very big number is still a big number. ;-) -- Keir