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Re: [Xen-devel] xm mem-max and mem-set

To: Anthony Liguori <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-devel] xm mem-max and mem-set
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 14 Apr 2006 07:55:28 +0100
Cc: Ky Srinivasan <ksrinivasan@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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On 14 Apr 2006, at 02:48, Anthony Liguori wrote:

I'm slightly concerned about the subtle race condition it would introduce. If there's no reason to set max-mem below current reservation (if it causes crashes which I don't really understand why it would) then I think it would be something best enforced within the hypervisor.

Why, exactly, would setting max-mem below the current reservation cause problems in the guest? I guess it may fail because of grant transfer ops (in which case, we really ought to enforce it at the hypervisor level).

xen_create_contiguous_region() will get *quite* upset if it gives up memory pages to Xen in good faith and gets nothing in return. :-)

Not allowing max allocation to be set lower than current allocation sounds like a sensible enforcement for the hypervisor, and I think that should avoid crashes.

 -- Keir

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