From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id E68D190015D for ; Wed, 22 Jun 2011 02:39:11 -0400 (EDT) Received: by iyl8 with SMTP id 8so571835iyl.14 for ; Tue, 21 Jun 2011 23:39:09 -0700 (PDT) From: Nai Xia Reply-To: nai.xia@gmail.com Subject: Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte and mmu notifier to help KSM dirty bit tracking Date: Wed, 22 Jun 2011 14:38:55 +0800 References: <201106212055.25400.nai.xia@gmail.com> <20110622002123.GP25383@sequoia.sous-sol.org> <4E018897.7040707@ravellosystems.com> In-Reply-To: <4E018897.7040707@ravellosystems.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Message-Id: <201106221438.55516.nai.xia@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Izik Eidus Cc: Chris Wright , Andrew Morton , Andrea Arcangeli , Hugh Dickins , Rik van Riel , linux-mm , Johannes Weiner , linux-kernel , kvm , mtosatti@redhat.com On Wednesday 22 June 2011 14:15:51 Izik Eidus wrote: > On 6/22/2011 3:21 AM, Chris Wright wrote: > > * Nai Xia (nai.xia@gmail.com) wrote: > >> Introduced kvm_mmu_notifier_test_and_clear_dirty(), kvm_mmu_notifier_dirty_update() > >> and their mmu_notifier interfaces to support KSM dirty bit tracking, which brings > >> significant performance gain in volatile pages scanning in KSM. > >> Currently, kvm_mmu_notifier_dirty_update() returns 0 if and only if intel EPT is > >> enabled to indicate that the dirty bits of underlying sptes are not updated by > >> hardware. > > Did you test with each of EPT, NPT and shadow? > > > >> Signed-off-by: Nai Xia > >> Acked-by: Izik Eidus > >> --- > >> arch/x86/include/asm/kvm_host.h | 1 + > >> arch/x86/kvm/mmu.c | 36 +++++++++++++++++++++++++++++ > >> arch/x86/kvm/mmu.h | 3 +- > >> arch/x86/kvm/vmx.c | 1 + > >> include/linux/kvm_host.h | 2 +- > >> include/linux/mmu_notifier.h | 48 +++++++++++++++++++++++++++++++++++++++ > >> mm/mmu_notifier.c | 33 ++++++++++++++++++++++++++ > >> virt/kvm/kvm_main.c | 27 ++++++++++++++++++++++ > >> 8 files changed, 149 insertions(+), 2 deletions(-) > >> > >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > >> index d2ac8e2..f0d7aa0 100644 > >> --- a/arch/x86/include/asm/kvm_host.h > >> +++ b/arch/x86/include/asm/kvm_host.h > >> @@ -848,6 +848,7 @@ extern bool kvm_rebooting; > >> int kvm_unmap_hva(struct kvm *kvm, unsigned long hva); > >> int kvm_age_hva(struct kvm *kvm, unsigned long hva); > >> int kvm_test_age_hva(struct kvm *kvm, unsigned long hva); > >> +int kvm_test_and_clear_dirty_hva(struct kvm *kvm, unsigned long hva); > >> void kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte); > >> int cpuid_maxphyaddr(struct kvm_vcpu *vcpu); > >> int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu); > >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > >> index aee3862..a5a0c51 100644 > >> --- a/arch/x86/kvm/mmu.c > >> +++ b/arch/x86/kvm/mmu.c > >> @@ -979,6 +979,37 @@ out: > >> return young; > >> } > >> > >> +/* > >> + * Caller is supposed to SetPageDirty(), it's not done inside this. > >> + */ > >> +static > >> +int kvm_test_and_clear_dirty_rmapp(struct kvm *kvm, unsigned long *rmapp, > >> + unsigned long data) > >> +{ > >> + u64 *spte; > >> + int dirty = 0; > >> + > >> + if (!shadow_dirty_mask) { > >> + WARN(1, "KVM: do NOT try to test dirty bit in EPT\n"); > >> + goto out; > >> + } > > This should never fire with the dirty_update() notifier test, right? > > And that means that this whole optimization is for the shadow mmu case, > > arguably the legacy case. > > > > Hi Chris, > AMD npt does track the dirty bit in the nested page tables, > so the shadow_dirty_mask should not be 0 in that case... > Hi Izik, I think he meant that if the caller is doing right && (!shadow_dirty_mask), the kvm_test_and_clear_dirty_rmapp() will never be called at all. So this test inside kvm_test_and_clear_dirty_rmapp() is useless...as I said I added this test in any case of this interface abused by others, just like a softer BUG_ON() --- dirty bit is not that critical to bump into BUG(). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org