linux-kernel - Re: [PATCH 4/5] KVM: MMU: store generation-number into mmio spte

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Date:	Mon, 18 Mar 2013 14:48:54 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 4/5] KVM: MMU: store generation-number into mmio spte

On Mon, Mar 18, 2013 at 08:42:09PM +0800, Xiao Guangrong wrote:
> On 03/18/2013 07:19 PM, Paolo Bonzini wrote:
> > Il 15/03/2013 16:29, Xiao Guangrong ha scritto:
> >> +/*
> >> + * spte bits of bit 3 ~ bit 11 are used as low 9 bits of
> >> + * generation, the bits of bits 52 ~ bit 61 are used as
> >> + * high 12 bits of generation.
> >> + */
> > 
> > High 10 bits.
> 
> Yes, i forgot to update the comments! Thank you, Paolo!
> 
> > 
> > How often does the generation number change?  Especially with Takuya's
> > patches, using just 10 bits for the generation might be enough and
> > simplifies the code.
> 
> I guess it's only updated when guest is initializing and doing hotplug.
> In my origin thought, if the number is big enough that it could not
> round on all most case of hotplug, the things introduced by Takuya is
> not necessary. But, if you guys want to keep the things, 10 bits should
> be enough. :)
I think you encapsulated the 19bit generation number handling good enough, so
I personally do not mind making it as big as we can.

--
			Gleb.
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