linux-kernel - Re: [PATCH v3 06/15] KVM: MMU: redesign the algorithm of pte

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Date:	Mon, 18 Nov 2013 22:48:13 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	gleb@...hat.com, avi.kivity@...il.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 06/15] KVM: MMU: redesign the algorithm of pte_list

On Wed, Oct 23, 2013 at 09:29:24PM +0800, Xiao Guangrong wrote:
> Change the algorithm to:
> 1) always add new desc to the first desc (pointed by parent_ptes/rmap)
>    that is good to implement rcu-nulls-list-like lockless rmap
>    walking
> 
> 2) always move the entry in the first desc to the the position we want
>    to remove when delete a spte in the parent_ptes/rmap （backward-move).
>    It is good for us to implement lockless rmap walk since in the current
>    code, when a spte is deleted from the "desc", another spte in the last
>    "desc" will be moved to this position to replace the deleted one. If the
>    deleted one has been accessed and we do not access the replaced one, the
>    replaced one is missed when we do lockless walk.
>    To fix this case, we do not backward move the spte, instead, we forward
>    move the entry: when a spte is deleted, we move the entry in the first
>    desc to that position
> 
> Both of these also can reduce cache miss
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>

Reviewed-by: Marcelo Tosatti <mtosatti@...hat.com>

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