Subject: Re: [PATCH -V3 2/4] powerpc/kvm: Contiguous memory allocator based hash page table allocation

From: Alexander Graf <[email-masked]>
Date: Tue, 02 Jul 2013 17:32:57 +0200

On 07/02/2013 05:31 PM, Aneesh Kumar K.V wrote:
> Alexander Graf<[email-masked]>  writes:
>
>> On 07/02/2013 07:45 AM, Aneesh Kumar K.V wrote:
>>> From: "Aneesh Kumar K.V"<[email-masked]>
>>>
>>> Powerpc architecture uses a hash based page table mechanism for mapping virtual
>>> addresses to physical address. The architecture require this hash page table to
>>> be physically contiguous. With KVM on Powerpc currently we use early reservation
>>> mechanism for allocating guest hash page table. This implies that we need to
>>> reserve a big memory region to ensure we can create large number of guest
>>> simultaneously with KVM on Power. Another disadvantage is that the reserved memory
>>> is not available to rest of the subsystems and and that implies we limit the total
>>> available memory in the host.
>>>
>>> This patch series switch the guest hash page table allocation to use
>>> contiguous memory allocator.
>>>
>>> Signed-off-by: Aneesh Kumar K.V<[email-masked]>
>> Is CMA a mandatory option in the kernel? Or can it be optionally
>> disabled? If it can be disabled, we should keep the preallocated
>> fallback case around for systems that have CMA disabled.
>>
> CMA is not a mandatory option. But we have
>
> config KVM_BOOK3S_64_HV
> 	bool "KVM support for POWER7 and PPC970 using hypervisor mode in host"
> 	depends on KVM_BOOK3S_64
> 	select MMU_NOTIFIER
> 	select CMA
>
> ie, for book3s HV we select CMA and only this CMA needs is memblock
> which we already support

Ah, that was the hunk I did miss. Thanks a lot, then it's perfectly fine 
of course :). Very nice patch set btw.

Alex