From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladimir Zidar Subject: Re: hypervisor memory usage Date: Wed, 28 Oct 2009 10:53:51 +0100 Message-ID: <4AE814AF.3020800@mindnever.org> References: <4AE80F01.1090602@mindnever.org> <20091028094543.GX1434@reaktio.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20091028094543.GX1434@reaktio.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org What bothers me with this issue is that memory is 'lost' just after=20 boot, without any of domUs running. Also, 8kb per 1MB would add up to 64MB per 8GB of ram, then I add 1=20 more MB for dom0 (when counted as guest). Global hypervisor memory, that is question now, can it use 384MB=20 straight after boot? - memory loss is detected at very first lines of=20 dom0 dmesg. Is there a way to show more xen debugging before dom0 kicks in? Pasi K=E4rkk=E4inen wrote: > On Wed, Oct 28, 2009 at 10:29:37AM +0100, Vladimir Zidar wrote: > =20 >> Hi, >> >> ** I sent this mail originally to xen-users, but after seeing other=20 >> subjects posted on that list I felt that it was kind of wrong place to= =20 >> ask ** >> >> >> I'm wondering why hypervisor itself uses so much memory? Is it normal? >> >> I have several servers with 8GB of ram, all of them running x86_64 >> centos 5.4 (latest) and when running under xen, dom0 has >> [root@palmae ~]# head -4 /proc/meminfo >> MemTotal: 7661568 kB >> MemFree: 6550044 kB >> Buffers: 37400 kB >> Cached: 303480 kB >> >> Which is 440MB less than what I get without xen. >> It comes down to what amount of memory kernel gets either from Xen or >> from BIOS. Please note the differences: >> >> =20 > > First of all you should limit the amount of memory visible to dom0 by > specifying dom0_mem=3D512M (or so) parameter for xen.gz in grub.conf. > > After that reboot and then you can check the Xen hypervisor free memory= with=20 > "xm info" and list the guest/domain mem usage with "xm list". > > Xen has some memory overhead (just like every virtualization solution). > > I think the formula for Xen memory overhead is: 8kB per 1MB of guest > memory, plus 1MB per guest virtual cpu.=20 > > I think this also applies to dom0, since basicly it is just a guest=20 > (with some more privileges). > > And in addition of course there is the "global" hypervisor memory > usage.. not sure if those will add up to 440 MB though. > > -- Pasi > > =20