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] Re: [Xen-users] Max. PV and HVM Guests

To: Pasi Kärkkäinen <pasik@xxxxxx>, Nick Couchman <Nick.Couchman@xxxxxxxxx>
Subject: Re: [Xen-devel] Re: [Xen-users] Max. PV and HVM Guests
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 09 Nov 2009 15:24:59 +0000
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Mr. Teo En Ming \(Zhang Enming\)" <space.time.universe@xxxxxxxxx>, "xen-users@xxxxxxxxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxxxxxxxx>, Robert Dunkley <Robert@xxxxxxxxx>
Delivery-date: Mon, 09 Nov 2009 07:25:46 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <20091109151750.GN16033@xxxxxxxxxxx>
List-help: <mailto:xen-users-request@lists.xensource.com?subject=help>
List-id: Xen user discussion <xen-users.lists.xensource.com>
List-post: <mailto:xen-users@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-users>, <mailto:xen-users-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcphUCj+XZuboHfgSsSM0LLWKtCIfQAAKOH1
Thread-topic: [Xen-devel] Re: [Xen-users] Max. PV and HVM Guests
User-agent: Microsoft-Entourage/
On 09/11/2009 15:17, "Pasi Kärkkäinen" <pasik@xxxxxx> wrote:

>> Furthermore, while I'm not
>> Linux developer and so not familiar with how Linux calculates buffering
>> and caching, I do know that my Linux systems dynamically manage buffers
>> and caches, and when memory is reduced or some application requires a
>> larger amount of physical memory, Linux reduces the amount of data in
>> buffers and caches.
> Yeah, it has to do with sizing the network buffers, caches etc..
> It shouldn't _crash_, so Teo is seeing some bug I believe. But it has
> always been "best practice" to limit dom0 memory - and prevent weird
> things happening later (like "memory squeeze in netback driver").

The issue is not really kernel data like network buffers and buffer cache.
It is kernel memory metadata -- primarily the per-page info structure that
the kernel maintains. The metadata doesn't get shrunk with memory size when
ballooning out, hence it increases as a proportion of memory still assigned
to the domain. That really is significant when aggressively ballooning down
a large-memory domain.

 -- Keir

Xen-users mailing list