linux-kernel - Re: [Xen-devel] [RFC PATCH] Boot PV guests with more than 128GB (v1) for 3.7

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Message-Id: <501286E50200007800090ECB@nat28.tlf.novell.com>
Date:	Fri, 27 Jul 2012 11:17:41 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Ian Campbell" <Ian.Campbell@...rix.com>
Cc:	"Ian Jackson" <Ian.Jackson@...citrix.com>,
	"xen-devel" <xen-devel@...ts.xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [RFC PATCH] Boot PV guests with more than
 128GB (v1) for 3.7

>>> On 27.07.12 at 12:00, Ian Campbell <Ian.Campbell@...rix.com> wrote:
> On Fri, 2012-07-27 at 08:34 +0100, Jan Beulich wrote:
>> >>> On 26.07.12 at 22:47, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
>> >  2). Allocate a new array, copy the existing P2M into it,
>> >     revector the P2M tree to use that, and return the old
>> >     P2M to the memory allocate. This has the advantage that
>> >     it sets the stage for using XEN_ELF_NOTE_INIT_P2M
>> >     feature. That feature allows us to set the exact virtual
>> >     address space we want for the P2M - and allows us to
>> >     boot as initial domain on large machines.
>> 
>> And I would hope that the tools would get updated to recognize
>> this note too, so that huge DomU-s would become possible as
>> well.
> 
> Does this help us with >160GB 32 bit PV guests too? I'm guessing not
> since the real limitation there is the relatively small amount of kernel
> address space.

Correct - 32-bit PV guests are limited anyway (and it's for a
reason the Dom0 support in the hypervisor only deals with
64-bit ones). And honestly, considering the huge page
information table such a memory amount would require, I
doubt this big a PV guest would even boot (or if it does, be
of any use).

Jan

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