Re: [Xen-devel] a ton of kernel issues

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 14/12/11 12:16, Ian Campbell wrote:
> On Wed, 2011-12-14 at 07:25 +0000, Ian Campbell wrote:
>>
>> It controls precisely the behaviour you need! Try "maxmem=2048" and
>> "memory=1024" in your guest configuration, it should boot with 1G of
>> RAM and allow you to balloon to 2G and back. 
> 
> I take it back, there is indeed a bug in the PV ops kernel in this
> regard.
> 
> It works with xm/xend because they set the maximum reservation for
> guests to static-max on boot. xl (and, I think, xapi) instead set the
> maximum reservation to the current balloon target and change it
> dynamically as the target is changed (as a method of enforcing the
> targets). However the pvops kernel incorrectly uses the maximum
> reservation at boot to size the physical address space for guests.
> 
> The patch below fixes this.
> 
> Ian.
> 
> 8<-------------------------------------------------------------
> 
> From 649ca3b7ddca1cdda85c27e34f806f30484172ec Mon Sep 17 00:00:00 2001
> From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Date: Wed, 14 Dec 2011 12:00:38 +0000
> Subject: [PATCH] xen: only limit memory map to maximum reservation for domain 
> 0.
> 
> d312ae878b6a "xen: use maximum reservation to limit amount of usable RAM"
> clamped the total amount of RAM to the current maximum reservation. This is
> correct for dom0 but is not correct for guest domains. In order to boot a 
> guest
> "pre-ballooned" (e.g. with memory=1G but maxmem=2G) in order to allow for
> future memory expansion the guest must derive max_pfn from the e820 provided 
> by
> the toolstack and not the current maximum reservation (which can reflect only
> the current maximum, not the guest lifetime max). The existing algorithm
> already behaves this correctly if we do not artificially limit the maximum
> number of pages for the guest case.
[...]
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxx
> Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Acked-by: David Vrabel <david.vrabel@xxxxxxxxxx>

or Reviewed-by if that's more appropriate.

David


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