linux-kernel - Re: [PATCH v3 07/15] KVM: MMU: introduce invalid rmap handlers

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Date:	Thu, 18 Apr 2013 11:15:37 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	gleb@...hat.com, avi.kivity@...il.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 07/15] KVM: MMU: introduce invalid rmap handlers

On 04/18/2013 07:38 AM, Marcelo Tosatti wrote:
> On Tue, Apr 16, 2013 at 02:32:45PM +0800, Xiao Guangrong wrote:
>> Invalid rmaps is the rmap of the invalid memslot which is being
>> deleted, especially, we can treat all rmaps are invalid when
>> kvm is being destroyed since all memslot will be deleted soon.
>> MMU should remove all sptes on these rmaps before the invalid
>> memslot fully deleted
>>
>> The reason why we separately handle invalid rmap is we want to
>> unmap invalid-rmap out of mmu-lock to achieve scale performance
>> on intensive memory and vcpu used guest
> 
> Better try to make the code simpler, and introduce complexity only 
> if necessary.

Marcelo,

This code is necessary to implement "unmap invalid rmap out of mmu-lock",
the reason why we need it is that ...

> 
> The idea to zap the roots is very elegant and apparently effective. What
> are its problems?

I mentioned it in 00/15:

* Challenges
Some page invalidation is requested when memslot is moved or deleted
and kvm is being destroy who call zap_all_pages to delete all sp using
their rmap and lpage-info, after call zap_all_pages, the rmap and lpage-info
will be freed. So, we should implement a fast way to delete sp from the rmap
and lpage-info.


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