From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932608AbdEDDhC (ORCPT ); Wed, 3 May 2017 23:37:02 -0400 Received: from mail-pf0-f195.google.com ([209.85.192.195]:36100 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932569AbdEDDgy (ORCPT ); Wed, 3 May 2017 23:36:54 -0400 Subject: Re: [PATCH 0/7] KVM: MMU: fast write protect To: Paolo Bonzini , mtosatti@redhat.com, avi.kivity@gmail.com, rkrcmar@redhat.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, Xiao Guangrong References: <20170503105224.19049-1-xiaoguangrong@tencent.com> <878cbc47-316c-d508-a5a3-22029dee2203@redhat.com> From: Xiao Guangrong Message-ID: <9af959d5-23c2-abd4-6100-577755239d2f@gmail.com> Date: Thu, 4 May 2017 11:36:55 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.0 MIME-Version: 1.0 In-Reply-To: <878cbc47-316c-d508-a5a3-22029dee2203@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/2017 10:57 PM, Paolo Bonzini wrote: > > > On 03/05/2017 16:50, Xiao Guangrong wrote: >> Furthermore, userspace has no knowledge about if PML is enable (it >> can be required from sysfs, but it is a good way in QEMU), so it is >> difficult for the usespace to know when to use write-protect-all. >> Maybe we can make KVM_CAP_X86_WRITE_PROTECT_ALL_MEM return false if >> PML is enabled? > > Yes, that's a good idea. Though it's a pity that, with PML, setting the > dirty bit will still do the massive walk of the rmap. At least with > reset_dirty_pages it's done a little bit at a time. > >>> Also, I wonder how the alternative write protection mechanism would >>> affect performance of the dirty page ring buffer patches. You would do >>> the write protection of all memory at the end of >>> kvm_vm_ioctl_reset_dirty_pages. You wouldn't even need a separate >>> ioctl, which is nice. On the other hand, checkpoints would be more >>> frequent and most pages would be write-protected, so it would be more >>> expensive to rebuild the shadow page tables... >> >> Yup, write-protect-all can improve reset_dirty_pages indeed, i will >> apply your idea after reset_dirty_pages is merged. >> >> However, we still prefer to have a separate ioctl for write-protect-all >> which cooperates with KVM_GET_DIRTY_LOG to improve live migration that >> should not always depend on checkpoint. > > Ok, I plan to merge the dirty ring pages early in 4.13 development. Great. As there is no conflict between these two patchsets except dirty ring pages takes benefit from write-protect-all, i think they can be developed and iterated independently, right? Or you prefer to merge dirty ring pages first then review the new version of this patchset later? Thanks! From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57062) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1d67ZZ-0006xG-PM for qemu-devel@nongnu.org; Wed, 03 May 2017 23:36:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1d67ZW-0003aK-N3 for qemu-devel@nongnu.org; Wed, 03 May 2017 23:36:57 -0400 Received: from mail-pf0-x243.google.com ([2607:f8b0:400e:c00::243]:34979) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1d67ZW-0003Zi-Fx for qemu-devel@nongnu.org; Wed, 03 May 2017 23:36:54 -0400 Received: by mail-pf0-x243.google.com with SMTP id o68so338430pfj.2 for ; Wed, 03 May 2017 20:36:54 -0700 (PDT) References: <20170503105224.19049-1-xiaoguangrong@tencent.com> <878cbc47-316c-d508-a5a3-22029dee2203@redhat.com> From: Xiao Guangrong Message-ID: <9af959d5-23c2-abd4-6100-577755239d2f@gmail.com> Date: Thu, 4 May 2017 11:36:55 +0800 MIME-Version: 1.0 In-Reply-To: <878cbc47-316c-d508-a5a3-22029dee2203@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 0/7] KVM: MMU: fast write protect List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , mtosatti@redhat.com, avi.kivity@gmail.com, rkrcmar@redhat.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, Xiao Guangrong On 05/03/2017 10:57 PM, Paolo Bonzini wrote: > > > On 03/05/2017 16:50, Xiao Guangrong wrote: >> Furthermore, userspace has no knowledge about if PML is enable (it >> can be required from sysfs, but it is a good way in QEMU), so it is >> difficult for the usespace to know when to use write-protect-all. >> Maybe we can make KVM_CAP_X86_WRITE_PROTECT_ALL_MEM return false if >> PML is enabled? > > Yes, that's a good idea. Though it's a pity that, with PML, setting the > dirty bit will still do the massive walk of the rmap. At least with > reset_dirty_pages it's done a little bit at a time. > >>> Also, I wonder how the alternative write protection mechanism would >>> affect performance of the dirty page ring buffer patches. You would do >>> the write protection of all memory at the end of >>> kvm_vm_ioctl_reset_dirty_pages. You wouldn't even need a separate >>> ioctl, which is nice. On the other hand, checkpoints would be more >>> frequent and most pages would be write-protected, so it would be more >>> expensive to rebuild the shadow page tables... >> >> Yup, write-protect-all can improve reset_dirty_pages indeed, i will >> apply your idea after reset_dirty_pages is merged. >> >> However, we still prefer to have a separate ioctl for write-protect-all >> which cooperates with KVM_GET_DIRTY_LOG to improve live migration that >> should not always depend on checkpoint. > > Ok, I plan to merge the dirty ring pages early in 4.13 development. Great. As there is no conflict between these two patchsets except dirty ring pages takes benefit from write-protect-all, i think they can be developed and iterated independently, right? Or you prefer to merge dirty ring pages first then review the new version of this patchset later? Thanks!