linux-kernel - Re: [PATCH 00/13] KVM: MMU: fast page fault

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Date:	Fri, 13 Apr 2012 23:25:28 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
Cc:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Xiao Guangrong <xiaoguangrong.eric@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 00/13] KVM: MMU: fast page fault

Xiao,

Takuya Yoshikawa <takuya.yoshikawa@...il.com> wrote:

> > What is your really want to say but i missed?
> 
> How to improve and what we should pay for that.
> 
> Note that I am not objecting to O(1) itself.
> 

I forgot to say one important thing -- I might give you wrong impression.

I am perfectly fine with your lock-less work.  It is really nice!

The reason I say much about O(1) is that O(1) and rmap based
GET_DIRTY_LOG have fundamentally different characteristics.

I am thinking really seriously how to make dirty page tracking work
well with QEMU in the future.

For example, I am thinking about multi-threaded and fine-grained
GET_DIRTY_LOG.

If we use rmap based GET_DIRTY_LOG, we can restrict write protection to
only a selected area of one guest memory slot.

So we may be able to make each thread process dirty pages independently
from other threads by calling GET_DIRTY_LOG for its own area.

But I know that O(1) has its own good point.
So please wait a bit.  I will write up what I am thinking or send patches.

Anyway, I am looking forward to your lock-less work!
It will improve the current GET_DIRTY_LOG performance.

Thanks,
	Takuya
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