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Re: [Xen-devel] Re: [PATCH v3 08/10] xen: use host E820 map for dom0

To: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH v3 08/10] xen: use host E820 map for dom0
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 20 Oct 2010 10:05:28 -0700
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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References: <alpine.DEB.2.00.1010121043030.2422@kaball-desktop> <1286901770-8612-8-git-send-email-Stefano.Stabellini@xxxxxxxxxxxxx> <20101018155412.GD27373@xxxxxxxxxxxx> <alpine.DEB.2.00.1010191148550.2423@kaball-desktop>
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 On 10/19/2010 03:49 AM, Stefano Stabellini wrote:
>>> -   e820_add_region(0, PFN_PHYS((u64)max_pfn), E820_RAM);
>>> -
>>> +   for (i = 0; i < memmap.nr_entries; i++) {
>>> +           unsigned long long end = map[i].addr + map[i].size;
>>> +           if (map[i].type == E820_RAM) {
>>> +                   if (map[i].addr > mem_end)
>>> +                           continue;
>> Would it make sense to print out a message saying something to the
>> effect of: "You need to increase the CONFIG_XEN_MAX_DOMAIN_MEMORY value to
>> take advantage of the extra %d gobs of memory!\n", map[i].size
>> Or will this be unneccessary with the later changes that Jeremy has
>> for the balloon work?
> I think it still makes a lot of sense to print that message because
> ballooning might be disabled.

CONFIG_XEN_MAX_DOMAIN_MEMORY scales the max pfn in the p2m table, and it
independent of whether ballooning is enabled.  The presence or absence
of ballooning will only affect whether memory between memory and maxmem
can be made available.  And it defaults 128G now anyway, so its very
unlikely people will hit it by accident.

Aside from that, I'm thinking of making ballooning mandatory (perhaps
just a config option on the usermode-visible parts), since it seems so
core (its mandatory for all the dom0/passthrough stuff anyway).


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