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Date: Mon, 25 Nov 2013 16:12:54 -0200
From: Marcelo Tosatti <mtosatti@redhat.com>
To: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Gleb Natapov <gleb@redhat.com>, avi.kivity@gmail.com,
        "pbonzini@redhat.com Bonzini" <pbonzini@redhat.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Eric Dumazet <dada1@cosmosbay.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 07/15] KVM: MMU: introduce nulls desc
Message-ID: <20131125181254.GB21858@amt.cnet>
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On Mon, Nov 25, 2013 at 02:29:03PM +0800, Xiao Guangrong wrote:
> >> Also, there is no guarantee of termination (as long as sptes are
> >> deleted with the correct timing). BTW, can't see any guarantee of
> >> termination for rculist nulls either (a writer can race with a lockless
> >> reader indefinately, restarting the lockless walk every time).
> > 
> > Hmm, that can be avoided by checking dirty-bitmap before rewalk,
> > that means, if the dirty-bitmap has been set during lockless write-protection,
> > it�s unnecessary to write-protect its sptes. Your idea?
> This idea is based on the fact that the number of rmap is limited by
> RMAP_RECYCLE_THRESHOLD. So, in the case of adding new spte into rmap,
> we can break the rewalk at once, in the case of deleting, we can only
> rewalk RMAP_RECYCLE_THRESHOLD times.

Please explain in more detail.