Re: [Xen-devel] hypervisor memory usage

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Oct 28, 2009 at 12:19:01PM +0100, Vladimir Zidar wrote:
> I have actually tracked this down to xen version which centos (could be 
> also what rhel uses):
> 

CentOS is (or, aims to be) 1:1 clone of RHEL.

> Version xen.gz-2.6.18-53.1.4.el5.centos.plus gives
> BIOS-provided physical RAM map:
> Xen: 0000000000000000 - 00000001f00cb000 (usable)
> On node 0 totalpages: 2031819
>  DMA zone: 2031819 pages, LIFO batch:31
> 
> and xen.gz-2.6.18-164.el5 gives:
> 
> BIOS-provided physical RAM map:
> Xen: 0000000000000000 - 00000001dc9c8000 (usable)
> On node 0 totalpages: 1952200
>  DMA zone: 1952200 pages, LIFO batch:31
> 
> That is 79619 pages difference - slightly over 300MB.
> 

Well.. that explains it..

> 
> Now I understand that this could be due to rhel patches, and maybe 
> doesn't relate to official xen builds, but I'd like to know if this 
> issue was known or not before jumping into xen 3.4 - as it won't be 
> direct rpm/yum upgrade path.
> 

RHEL 5.4 (-164 kernel) added more support for VT-d etc, so maybe that's why
more DMA memory is reserved. dunno.

-- Pasi


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