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

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 02 Jul 2013 21:01:37 +0530

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

-aneesh