linux-kernel - Re: [PATCH v5 0/8] KVM: MMU: fast zap all shadow pages

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Date:	Fri, 17 May 2013 02:26:12 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
CC:	gleb@...hat.com, avi.kivity@...il.com, mtosatti@...hat.com,
	pbonzini@...hat.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH v5 0/8] KVM: MMU: fast zap all shadow pages

On 05/16/2013 10:36 PM, Takuya Yoshikawa wrote:
> On Thu, 16 May 2013 20:17:45 +0800
> Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com> wrote:
> 
>> Bechmark result:
>> I have tested this patchset and the previous version that only zaps the
>> pages linked on invalid slot's rmap. The benchmark is written by myself
>> which has been attached, it writes large memory when do pci rom read.
>>
>> Host: Intel(R) Xeon(R) CPU X5690  @ 3.47GHz + 36G Memory
>> Guest: 12 VCPU + 32G Memory
>>
>> Current code:           This patchset         Previous Version 
>> 2405434959 ns           2323016424 ns         2368810003 ns
>>
>> The interesting thing is, the previous version is slower than this patch,
>> i guess the reason is that the former keeps lots of invalid pages in mmu
>> which cause shadow page to be reclaimed due to used-pages > request-pages
>> or host memory shrink.
> 
> This patch series looks very nice!

Thank you, Takuya!

> 
> Minor issues may still need to be improved, but I really hope to see this
> get merged during this cycle.
> 
> [for the future]  Do you think that postponing some zapping/freeing of
> obsolete(already invalidated) pages to make_mmu_pages_available() time
> can improve the situation more?  -- say, for big guests.

Yes, i think it can. :)

We have made many efforts on this but still lack a straight way to
achieve it.

> 
> If accounting kept correct, make_mmu_pages_available() only needs to free
> some obsolete pages instead of valid pages.
> 

Yes.


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