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] HVM and free_memory query

To: Apoorva Kulkarni <apoorva@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] HVM and free_memory query
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 10 Jul 2009 14:46:40 +0100
Delivery-date: Fri, 10 Jul 2009 06:47:25 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4A5644C8.4040306@xxxxxxxxx>
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>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcoBX64s4TaESSdgSqm8so1xit9JywABSvcI
Thread-topic: [Xen-devel] HVM and free_memory query
User-agent: Microsoft-Entourage/
On 09/07/2009 20:28, "Apoorva Kulkarni" <apoorva@xxxxxxxxx> 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

Xen-devel mailing list

<Prev in Thread] Current Thread [Next in Thread>