linux-kernel - Re: [PATCH] KVM: MMU: lazily drop large spte

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Message-ID: <20121112231032.GB5798@amt.cnet>
Date:	Mon, 12 Nov 2012 21:10:32 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: MMU: lazily drop large spte

On Mon, Nov 05, 2012 at 05:59:26PM +0800, Xiao Guangrong wrote:
> Do not drop large spte until it can be insteaded by small pages so that
> the guest can happliy read memory through it
> 
> The idea is from Avi:
> | As I mentioned before, write-protecting a large spte is a good idea,
> | since it moves some work from protect-time to fault-time, so it reduces
> | jitter.  This removes the need for the return value.
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> ---
>  arch/x86/kvm/mmu.c |   34 +++++++++-------------------------
>  1 files changed, 9 insertions(+), 25 deletions(-)

Its likely that other 4k pages are mapped read-write in the 2mb range 
covered by a read-only 2mb map. Therefore its not entirely useful to
map read-only. 

Can you measure an improvement with this change?


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