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KVM: MMU: zero caches before entering mmu_lock protected section

PATCH Marcelo Tosatti 2 participants 2 messages Jan 8, 2009

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x86 KVM KVM x86
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Marcelo Tosatti

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#0 lore raw

Clean the pre-allocated cache pages before entering mmu_lock region. This is safe since the caches are per-vcpu.

Smaller chunks are already zeroed by kmem_cache_zalloc.

~= 0.90% reduction in system time with AIM7 on RHEL3 / 4-vcpu.

Signed-off-by Marcelo Tosatti <[email protected]>
arch/x86/kvm/mmu.c +1 -2
index 10bdb2a..823d0cd 100644
@@ -301,7 +301,7 @@ static int mmu_topup_memory_cache_page(struct kvm_mmu_memory_cache *cache,
 	if (cache->nobjs >= min)
 		return 0;
 	while (cache->nobjs < ARRAY_SIZE(cache->objects)) {
-		page = alloc_page(GFP_KERNEL);
+		page = alloc_page(GFP_KERNEL|__GFP_ZERO);
 		if (!page)
 			return -ENOMEM;
 		set_page_private(page, 0);

@@ -352,7 +352,6 @@ static void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc,
 
 	BUG_ON(!mc->nobjs);
 	p = mc->objects[--mc->nobjs];
-	memset(p, 0, size);
 	return p;
 }
#1 lore raw
Quoted 24 lines · Marcelo Tosatti

Clean the pre-allocated cache pages before entering mmu_lock region. This is safe since the caches are per-vcpu.

Smaller chunks are already zeroed by kmem_cache_zalloc.

~= 0.90% reduction in system time with AIM7 on RHEL3 / 4-vcpu.

Signed-off-by Marcelo Tosatti <[email protected]>
arch/x86/kvm/mmu.c +1 -1
index 10bdb2a..823d0cd 100644
@@ -301,7 +301,7 @@ static int mmu_topup_memory_cache_page(struct kvm_mmu_memory_cache *cache,
 	if (cache->nobjs >= min)
 		return 0;
 	while (cache->nobjs < ARRAY_SIZE(cache->objects)) {
-		page = alloc_page(GFP_KERNEL);
+		page = alloc_page(GFP_KERNEL|__GFP_ZERO);
 		if (!page)
 			return -ENOMEM;
 		set_page_private(page, 0);

arch/x86/kvm/mmu.c static void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc, · line 357

Quoted 7 lines
arch/x86/kvm/mmu.c +0 -1
@@ -352,7 +352,6 @@ static void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc,
 
 	BUG_ON(!mc->nobjs);
 	p = mc->objects[--mc->nobjs];
-	memset(p, 0, size);
 	return p;
 }

I think we can drop the memset altogether, since we will clear the page in ->prefetch_page() anyway.

Signature · 2 lines
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.