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

On 07/02/2013 05:31 PM, Aneesh Kumar K.V wrote:

Alexander Graf[off-list ref]  writes:

quoted

On 07/02/2013 07:45 AM, Aneesh Kumar K.V wrote:

quoted

From: "Aneesh Kumar K.V"<redacted>

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<redacted>

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