From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH] KVM: MMU: lazily drop large spte Date: Mon, 12 Nov 2012 21:10:32 -0200 Message-ID: <20121112231032.GB5798@amt.cnet> References: <50978DFE.1000005@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , LKML , KVM To: Xiao Guangrong Return-path: Content-Disposition: inline In-Reply-To: <50978DFE.1000005@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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 > --- > 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?