From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934781Ab3FSMoI (ORCPT ); Wed, 19 Jun 2013 08:44:08 -0400 Received: from e23smtp07.au.ibm.com ([202.81.31.140]:53601 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934566Ab3FSMoF (ORCPT ); Wed, 19 Jun 2013 08:44:05 -0400 Message-ID: <51C1A78D.9050709@linux.vnet.ibm.com> Date: Wed, 19 Jun 2013 20:43:57 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Paolo Bonzini CC: gleb@redhat.com, avi.kivity@gmail.com, mtosatti@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 3/7] KVM: MMU: document write_flooding_count References: <1371632965-20077-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <1371632965-20077-4-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <51C19CD2.3080608@redhat.com> In-Reply-To: <51C19CD2.3080608@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13061912-0260-0000-0000-0000032F2CC7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/19/2013 07:58 PM, Paolo Bonzini wrote: > Il 19/06/2013 11:09, Xiao Guangrong ha scritto: >> Document write_flooding_count to Documentation/virtual/kvm/mmu.txt >> >> Signed-off-by: Xiao Guangrong >> --- >> Documentation/virtual/kvm/mmu.txt | 8 ++++++++ >> arch/x86/include/asm/kvm_host.h | 5 +++++ >> 2 files changed, 13 insertions(+) >> >> diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt >> index ce6df51..5a6b2e2 100644 >> --- a/Documentation/virtual/kvm/mmu.txt >> +++ b/Documentation/virtual/kvm/mmu.txt >> @@ -214,6 +214,14 @@ Shadow pages contain the following information: >> It is only used on 32bit host which helps us to detect whether updating the >> 64bit spte is complete so that we can avoid reading the truncated value out >> of mmu-lock. >> + write_flooding_count: >> + In order to sync the page table between guest and host, the page sometimes >> + needs to be write-protected (see "Synchronized and unsynchronized pages" >> + below), any write to the page can cause write emulation. If the emulation >> + on the page is too frequent we'd better unmap the page to avoid the >> + future emulation. write_flooding_count aims at this optimization which is >> + increased when the page needs to be write emulated and cleared when the >> + page is actually used. > > A guest may write to a page table many times, causing a lot of > emulations if the page needs to be write-protected (see "Synchronized > and unsynchronized pages" below). Leaf pages can be unsynchronized > so that they do not trigger frequent emulation, but this is not > possible for non-leafs. This field counts the number of emulations > since the last time the page table was actually used; if emulation > is triggered too frequently on this page, KVM will unmap the page > to avoid emulation in the future. very nice. > >> Reverse map >> =========== >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >> index 1dac2c1..5eb5382 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -234,6 +234,11 @@ struct kvm_mmu_page { >> int clear_spte_count; >> #endif >> >> + /* >> + * Increased when the page needs to be write emulated, cleared >> + * when the page is actually used as page table to avoid frequent >> + * emulation on the page. >> + */ > > /* Number of writes since the last time traversal visited this page. */ > > wdyt, better or worse? I think it is better. :) Thanks for your refining.