Re: [Patch v2 2/2] KVM: x86/mmu: Allocate page table pages on NUMA node of underlying pages

David Matlack
2022-12-09T00:28:06Z

On Thu, Dec 01, 2022 at 11:57:18AM -0800, Vipin Sharma wrote:
> Page table pages of a VM are currently allocated based on the current
> task's NUMA node or its mempolicy. This can cause suboptimal remote
> accesses by the vCPU if it is accessing physical pages local to its NUMA
> node but the page table pages mapping those physcal pages were created
> by some other vCPU which was on different NUMA node or had different
> policy.
>
> Allocate page table pages on the same NUMA node where underlying
> physical page exists. Page table at level 5, 4, and 3 might not end up
> on the same NUMA node as they can span multiple NUMA nodes.
>
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> ---
...
> @@ -6284,13 +6326,16 @@ static int shadow_mmu_try_split_huge_page(struct kvm *kvm,
> gfn = kvm_mmu_page_get_gfn(huge_sp, spte_index(huge_sptep));
> level = huge_sp->role.level;
> spte = *huge_sptep;
> + nid = kvm_pfn_to_refcounted_page_nid(spte_to_pfn(spte));
> + if (nid == NUMA_NO_NODE)
> + nid = numa_mem_id();

What do you think about renaming kvm_pfn_to_refcounted_page_nid() to
kvm_pfn_to_page_table_nid() and having it return numa_mem_id() instead
of NUMA_NO_NODE (with a comment)? I think that will clean up this patch
quite a bit by getting rid of all the NUMA_NO_NODE checks.