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

[David Vrabel]

On 03/05/12 12:48, David Vrabel wrote:
> On 01/05/12 17:37, Konrad Rzeszutek Wilk wrote:
>> 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".
> 
> It was tricky to track down what is going here but I think I see what's
> happening.
> 
> The problem pages (on the system I looked at) were located just before
> the ISA memory region (so PFN < a0) and so they are mapped in the
> bootstrap page tables and have an additional ref so are not immediately
> freed when the page is released.  They do get freed later on, presumably
> when the page tables are swapped over.

It's not the bootstrap page tables but those constructed in
xen_setup_kernel_pagetable() but this has the same effect.

> I think the mapping needs to be removed with
> HYPERVISOR_update_va_mapping() before releasing the page.  This is
> already done for the ISA region in xen_ident_map_ISA().

And here's a patch that does this.  I've not given it a lot of testing.

This is on top of your 8/8 patch and your "xen/setup: Cap amount to
populate based on current tot_pages count." patch is no longer needed.

David

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