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

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Date:   Thu, 8 Dec 2022 16:27:57 -0800
From:   David Matlack <dmatlack@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     bgardon@...gle.com, seanjc@...gle.com, pbonzini@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch v2 2/2] KVM: x86/mmu: Allocate page table pages on NUMA
 node of underlying pages

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@...gle.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.