Re: [PATCH] auto balloon initial domain and fix dom0_mem=Xinconsistencies (v5).

[Konrad Rzeszutek Wilk]

On Mon, Apr 16, 2012 at 01:15:31PM -0400, Konrad Rzeszutek Wilk wrote:
> Changelog v5 [since v4]:
>  - used populate_physmap, fixed bugs.
> [v2-v4: not posted]
>  - reworked the code in setup.c to work properly.
> [v1: https://lkml.org/lkml/2012/3/30/492]
>  - initial patchset

One bug I found was that with 'dom0_mem=max:1G' (with and without these
patches) I would get a bunch of

(XEN) page_alloc.c:1148:d0 Over-allocation for domain 0: 2097153 > 2097152
(XEN) memory.c:133:d0 Could not allocate order=0 extent: id=0 memflags=0 (0 of 17)

where the (0 of X), sometimes was 1, 2,3,4 or 17 -depending on the machine
I ran on it. I figured it out that the difference was in the ACPI tables
that are allocated - and that those regions - even though are returned
back to the hypervisor, cannot be repopulated. I can't find the actual
exact piece of code in the hypervisor to pin-point and say "Aha".

What I did was use the same metrix that the hypervisor uses to figure
out whether to deny the guest ballooning up - checking the d->tot_pages
against t->max_pages. For that the XENMEM_current_reservation is used.