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[Xen-devel] Re: [PATCH][v2.6.29][XEN] Return unused memory to hypervisor

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH][v2.6.29][XEN] Return unused memory to hypervisor
From: Miroslav Rezanina <mrezanin@xxxxxxxxxx>
Date: Fri, 21 Aug 2009 04:14:47 -0400 (EDT)
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Gianluca Guida <gianluca.guida@xxxxxxxxxx>
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----- Original Message -----
From: "Jeremy Fitzhardinge" <jeremy@xxxxxxxx>
To: "Miroslav Rezanina" <mrezanin@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, "Gianluca 
Guida" <gianluca.guida@xxxxxxxxxx>
Sent: Thursday, August 20, 2009 6:39:02 PM GMT +01:00 Amsterdam / Berlin / Bern 
/ Rome / Stockholm / Vienna
Subject: Re: [PATCH][v2.6.29][XEN] Return unused memory to hypervisor

On 08/20/09 00:47, Miroslav Rezanina wrote:
>> there is handled e820 map in guest. However, this patch informs 
>> hypervisor, that guest uses less memory than was assigned to it. 
>> If hypervisor is not informed, memory is reserved for guest that
>> do not need it. If hypervisor is informed, he decrease memory
>> reservation for guest and unused memory is marked as free 
>> for use by other guests.
> Yes.  But the guest will modify its own e820 map for a number of
> reasons; for example: reducing its own memory, or clearing a space for
> the PCI hole.  In general we want to free any underlying pages which
> don't correspond to E820_RAM regions.
>    J

I agree. However, I'm not sure if xen supports such a precise handling.
Miroslav Rezanina
Software Engineer - Virtualization Team - XEN kernel

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