linux-kernel - Re: [PATCH v5 8/8] KVM: MMU: zap pages in batch

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Date:	Thu, 16 May 2013 14:45:59 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
CC:	gleb@...hat.com, avi.kivity@...il.com, mtosatti@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v5 8/8] KVM: MMU: zap pages in batch

Il 16/05/2013 14:17, Xiao Guangrong ha scritto:
> Zap at lease 10 pages before releasing mmu-lock to reduce the overload
> caused by requiring lock
> 
> [ It improves kernel building 0.6% ~ 1% ]
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> ---
>  arch/x86/kvm/mmu.c |   11 ++++++++---
>  1 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index e12f431..9c27fda 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -4216,10 +4216,12 @@ restart:
>  	spin_unlock(&kvm->mmu_lock);
>  }
>  
> +#define BATCH_ZAP_PAGES	10
>  static void zap_invalid_pages(struct kvm *kvm)
>  {
>  	struct kvm_mmu_page *sp, *node;
>  	LIST_HEAD(invalid_list);
> +	int batch = 0;
>  
>  restart:
>  	list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) {
> @@ -4256,11 +4258,14 @@ restart:
>  		 * Need not flush tlb since we only zap the sp with invalid
>  		 * generation number.
>  		 */
> -		if (cond_resched_lock(&kvm->mmu_lock))
> +		if ((batch >= BATCH_ZAP_PAGES) &&
> +		      cond_resched_lock(&kvm->mmu_lock)) {
> +			batch = 0;
>  			goto restart;
> +		}
>  
> -		if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list))
> -			goto restart;
> +		batch += kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
> +		goto restart;

Would this look again and again at the same page if
kvm_mmu_prepare_zap_page returns 0?

Paolo

>  	}
>  
>  	/*
> 

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