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

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Date:   Thu, 16 Apr 2020 16:09:39 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Keqian Zhu <zhukeqian1@...wei.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Will Deacon <will@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jay Zhou <jianjay.zhou@...wei.com>, wanghaibin.wang@...wei.com
Subject: Re: [PATCH v2] KVM/arm64: Support enabling dirty log gradually in
 small chunks

On Wed, 15 Apr 2020 18:13:56 +0200
Paolo Bonzini <pbonzini@...hat.com> 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@...wei.com>
> > ---
> >  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?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...