linux-kernel - [Patch v3 9/9] KVM: x86/mmu: Reduce default cache size in KVM from 40 to PT64_ROOT_MAX

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Date:   Wed, 21 Dec 2022 18:34:57 -0800
From:   Vipin Sharma <vipinsh@...gle.com>
To:     seanjc@...gle.com, pbonzini@...hat.com, bgardon@...gle.com,
        dmatlack@...gle.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vipin Sharma <vipinsh@...gle.com>
Subject: [Patch v3 9/9] KVM: x86/mmu: Reduce default cache size in KVM from 40
 to PT64_ROOT_MAX_LEVEL

KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE is set to 40 without any specific
reason. Reduce default size to PT64_ROOT_MAX_LEVEL, which is currently
5.

Change mmu_pte_list_desc_cache size to what is needed as it is more than
5 but way less than 40.

Tested by running dirty_log_perf_test on both tdp and shadow MMU with 48
vcpu and 2GB/vcpu size on a 2 NUMA node machine. No impact on
performance noticed.

Ran perf on dirty_log_perf_test and found kvm_mmu_get_free_page() calls
reduced by ~3300 which is near to 48 (vcpus) * 2 (nodes) * 35 (cache
size).

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
---
 arch/x86/include/asm/kvm_types.h | 2 +-
 arch/x86/kvm/mmu/mmu.c           | 7 ++++---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_types.h b/arch/x86/include/asm/kvm_types.h
index 08f1b57d3b62..752dab218a62 100644
--- a/arch/x86/include/asm/kvm_types.h
+++ b/arch/x86/include/asm/kvm_types.h
@@ -2,6 +2,6 @@
 #ifndef _ASM_X86_KVM_TYPES_H
 #define _ASM_X86_KVM_TYPES_H
 
-#define KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE 40
+#define KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE PT64_ROOT_MAX_LEVEL
 
 #endif /* _ASM_X86_KVM_TYPES_H */
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7454bfc49a51..f89d933ff380 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -677,11 +677,12 @@ static int mmu_topup_sp_memory_cache(struct kvm_mmu_memory_cache *cache,
 
 static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
 {
-	int r, nid;
+	int r, nid, desc_capacity;
 
 	/* 1 rmap, 1 parent PTE per level, and the prefetched rmaps. */
-	r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache,
-				       1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM);
+	desc_capacity = 1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM;
+	r = __kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache,
+					 desc_capacity, desc_capacity);
 	if (r)
 		return r;
 
-- 
2.39.0.314.g84b9a713c41-goog