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RE: [Xen-devel] [PATCH] PoD: Handle operations properly when domain is d

To: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] PoD: Handle operations properly when domain is dying
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Wed, 11 Nov 2009 15:34:59 -0800 (PST)
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> From: George Dunlap [mailto:George.Dunlap@xxxxxxxxxxxxx]
> On Wed, Nov 11, 2009 at 5:58 PM, Dan Magenheimer
> <dan.magenheimer@xxxxxxxxxx> wrote:
> > Thanks for the detailed explanation.  I think
> > "Populate on Demand" connotes too much like
> > "Copy on Write" and doesn't really describe
> > the essence of what is going on: Booting pre-ballooned.
> > Thus my confusion.
> Well, "populate on demand" describes exactly what's actually
> happening: the p2m table is being populated as it's used, as opposed
> to being populated all at once at the beginning.  If it was allocating
> memory on demand it would have been called "allocate on demand". :-)

I understand that from your (developer's) point of view
but 99% or more of your customers won't know what a p2m
table is or what populating it means and will assume
(as I did earlier), since this is a memory-related
feature, that "populate" refers to utilizing RAM.

It's a cool and valuable feature... I just
think it deserves a better name. ;-)

> > This is of course less than ideal as it ensures that
> > administrators will choose some safe (probably fairly large)
> > amount of memory, a significant portion of which will often
> > be wasted.  But I suppose its better than the (much larger)
> > alternative.
> PoD is only meant to keep the domain going until the balloon driver
> loads, which should be fairly early in boot.  How much is required
> changes depending on the OS and the maximum amount of memory;  For
> Windows XP, 32-bit, with 4GiB maximum (i.e., reported in the e820
> map), 256 KiB is sufficient to start with (if I recall correctly).
> For Windows 7, that's a lot higher.  I forget the exact number, but
> it's 1-2GiB to boot with a 4GiB maximum.  Citrix is doing extensive
> testing to find out minimums for a large number of configurations, so
> that administrators using XenServer can confidently set the value to a
> minimum knowing that they're neither wasting memory nor risking a
> crash. :-)

I guess that makes sense in the Windows world where "distros"
can be counted on one or two hands.


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