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RE: [Xen-devel] comment request: dom0 dma on large memory systems

To: "Scott Parish" <srparish@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] comment request: dom0 dma on large memory systems
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Sat, 4 Jun 2005 11:48:16 +0800
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Thread-topic: [Xen-devel] comment request: dom0 dma on large memory systems
----Original Message-----
>From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Scott
>Sent: Friday, June 03, 2005 3:35 PM
>On x86_64 with 6gig ram, dom0's initial allocation is from memory
>above the pci hole (referred to as "high memory" in this email) if
>dom0_mem is set to 2g or higher. The only problem is that most io/dma
>devices (non-dac) can only dma to the first 32bits worth of machine
>addresses--thus for some configurations, dom0 has no memory which is

IIRC, 2 or 3 months ago, Keir said that default memory allocation for
Dom0 is all available memory. And then CP has to decrease by balloon
interface before creating other domains. If this still holds true, I'm
not sure whether above problem still exists, since all avail memory
including both <4G and >4G belonging to Dom0 then. (XEN itself only
consumes a small trunk). However after looking at your patch and then
the source, it seems that only the max available order, meaning must be
continuous, is allocated to Dom0 currently. So did I misunderstand this
concept? If it really only means maximum continuous trunk, then you
patch definitely shoots straight on the real problem on all 64bit
platform. ;-)


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