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] [PATCH] Disallow setting maxmem to higher value than tot

To: Michal Novotny <minovotn@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Disallow setting maxmem to higher value than total physical memory size
From: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Date: Wed, 1 Sep 2010 16:20:25 +0100
Cc: "'xen-devel@xxxxxxxxxxxxxxxxxxx'" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Wed, 01 Sep 2010 08:22:19 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4C7E60D0.8050706@xxxxxxxxxx>
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>
Organization: Citrix Systems, Inc.
References: <4C7E47B2.9010805@xxxxxxxxxx> <1283345049.12544.9494.camel@xxxxxxxxxxxxxxxxxxxxxx> <4C7E4EAD.3060106@xxxxxxxxxx> <1283348230.12544.9506.camel@xxxxxxxxxxxxxxxxxxxxxx> <4C7E60D0.8050706@xxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
On Wed, 2010-09-01 at 15:18 +0100, Michal Novotny wrote:

> Oh, ok. It's not limited to dom0 nevertheless I don't see anything to be 
> causing anything bad in domU. Of course, I can limit this to dom0 but 
> for domU you can be having e.g. this:
> 1)
> dom0: total memory = 8192
> domU: memory = 4096, maxmem = 8192 (xm mem-max domU 16384 fails)

It is useful, legal and valid to set e.g. maxmem = 12288 here, leaving
memory = 4096. Your patch prevents that.

> 2)
> and when you migrate to host B:
> dom0: total memory = 16384
> domU: memory = 4096, maxmem = 8192

If maxmem = 12288 then it would be possible to balloon this guest up to
12288 on this system. With your patch it is no longer possible. Note
that maxmem cannot change once the domU is booted so it needs to have
been = 12288 at the time the guest was created on Host A.

> Or should I just ignore the possibility domU maxmem could be set to 
> higher value than host machine could provide and should I limit my check 
> to dom0 only?


I haven't considered the applicability of this patch to dom0
particularly deeply but it is wrong to enforce this constraint on domUs.


Xen-devel mailing list

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