Re: [PATCH v2] KVM/arm64: Support enabling dirty log gradually in small chunks

[Paolo Bonzini]

On 16/04/20 17:09, Marc Zyngier wrote:
> On Wed, 15 Apr 2020 18:13:56 +0200
> Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> 
>> On 13/04/20 14:20, Keqian Zhu wrote:
>>> There is already support of enabling dirty log graually in small chunks
>>> for x86 in commit 3c9bd4006bfc ("KVM: x86: enable dirty log gradually in
>>> small chunks"). This adds support for arm64.
>>>
>>> x86 still writes protect all huge pages when DIRTY_LOG_INITIALLY_ALL_SET
>>> is eanbled. However, for arm64, both huge pages and normal pages can be
>>> write protected gradually by userspace.
>>>
>>> Under the Huawei Kunpeng 920 2.6GHz platform, I did some tests on 128G
>>> Linux VMs with different page size. The memory pressure is 127G in each
>>> case. The time taken of memory_global_dirty_log_start in QEMU is listed
>>> below:
>>>
>>> Page Size      Before    After Optimization
>>>   4K            650ms         1.8ms
>>>   2M             4ms          1.8ms
>>>   1G             2ms          1.8ms
>>>
>>> Besides the time reduction, the biggest income is that we will minimize
>>> the performance side effect (because of dissloving huge pages and marking
>>> memslots dirty) on guest after enabling dirty log.
>>>
>>> Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
>>> ---
>>>  Documentation/virt/kvm/api.rst    |  2 +-
>>>  arch/arm64/include/asm/kvm_host.h |  3 +++
>>>  virt/kvm/arm/mmu.c                | 12 ++++++++++--
>>>  3 files changed, 14 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
>>> index efbbe570aa9b..0017f63fa44f 100644
>>> --- a/Documentation/virt/kvm/api.rst
>>> +++ b/Documentation/virt/kvm/api.rst
>>> @@ -5777,7 +5777,7 @@ will be initialized to 1 when created.  This also improves performance because
>>>  dirty logging can be enabled gradually in small chunks on the first call
>>>  to KVM_CLEAR_DIRTY_LOG.  KVM_DIRTY_LOG_INITIALLY_SET depends on
>>>  KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (it is also only available on
>>> -x86 for now).
>>> +x86 and arm64 for now).
>>>  
>>>  KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the name
>>>  KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs that make
>>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>>> index 32c8a675e5a4..a723f84fab83 100644
>>> --- a/arch/arm64/include/asm/kvm_host.h
>>> +++ b/arch/arm64/include/asm/kvm_host.h
>>> @@ -46,6 +46,9 @@
>>>  #define KVM_REQ_RECORD_STEAL	KVM_ARCH_REQ(3)
>>>  #define KVM_REQ_RELOAD_GICv4	KVM_ARCH_REQ(4)
>>>  
>>> +#define KVM_DIRTY_LOG_MANUAL_CAPS   (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
>>> +				     KVM_DIRTY_LOG_INITIALLY_SET)
>>> +
>>>  DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
>>>  
>>>  extern unsigned int kvm_sve_max_vl;
>>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>>> index e3b9ee268823..1077f653a611 100644
>>> --- a/virt/kvm/arm/mmu.c
>>> +++ b/virt/kvm/arm/mmu.c
>>> @@ -2265,8 +2265,16 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>>>  	 * allocated dirty_bitmap[], dirty pages will be be tracked while the
>>>  	 * memory slot is write protected.
>>>  	 */
>>> -	if (change != KVM_MR_DELETE && mem->flags & KVM_MEM_LOG_DIRTY_PAGES)
>>> -		kvm_mmu_wp_memory_region(kvm, mem->slot);
>>> +	if (change != KVM_MR_DELETE && mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
>>> +		/*
>>> +		 * If we're with initial-all-set, we don't need to write
>>> +		 * protect any pages because they're all reported as dirty.
>>> +		 * Huge pages and normal pages will be write protect gradually.
>>> +		 */
>>> +		if (!kvm_dirty_log_manual_protect_and_init_set(kvm)) {
>>> +			kvm_mmu_wp_memory_region(kvm, mem->slot);
>>> +		}
>>> +	}
>>>  }
>>>  
>>>  int kvm_arch_prepare_memory_region(struct kvm *kvm,
>>>   
>>
>> Marc, what is the status of this patch?
> 
> I just had a look at it. Is there any urgency for merging it?

No, I thought I was still replying to the v1.

Paolo