Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932801AbcDTBlc (ORCPT ); Tue, 19 Apr 2016 21:41:32 -0400 Received: from mga02.intel.com ([134.134.136.20]:52857 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932568AbcDTBl3 convert rfc822-to-8bit (ORCPT ); Tue, 19 Apr 2016 21:41:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,507,1455004800"; d="scan'208";a="958648009" From: "Li, Liang Z" To: "Michael S. Tsirkin" CC: Rik van Riel , "viro@zeniv.linux.org.uk" , "linux-kernel@vger.kernel.org" , "quintela@redhat.com" , "amit.shah@redhat.com" , "pbonzini@redhat.com" , "dgilbert@redhat.com" , "linux-mm@kvack.org" , "kvm@vger.kernel.org" , "qemu-devel@nongnu.org" , "agraf@suse.de" , "borntraeger@de.ibm.com" Subject: RE: [PATCH kernel 1/2] mm: add the related functions to build the free page bitmap Thread-Topic: [PATCH kernel 1/2] mm: add the related functions to build the free page bitmap Thread-Index: AQHRmknpgl1kdv1qZESOs9NZnESE3J+Q3AOAgACHhcD//48GAIABHYtg Date: Wed, 20 Apr 2016 01:41:24 +0000 Message-ID: References: <1461076474-3864-1-git-send-email-liang.z.li@intel.com> <1461076474-3864-2-git-send-email-liang.z.li@intel.com> <1461077659.3200.8.camel@redhat.com> <20160419191111-mutt-send-email-mst@redhat.com> In-Reply-To: <20160419191111-mutt-send-email-mst@redhat.com> Accept-Language: zh-CN, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiZTM0NTVjNzUtNDYwMi00MGJmLWIyMDctZDhjN2M3ZWFiMTQ5IiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX0lDIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE1LjkuNi42IiwiVHJ1c3RlZExhYmVsSGFzaCI6Ik5zRnVMeDN3YlhQTnVpNVlIQmhBVlBuZlQwdERGb2l6TVwvVjhMNktWV1A4PSJ9 x-ctpclassification: CTP_IC x-originating-ip: [10.239.127.40] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1870 Lines: 47 > Cc: Rik van Riel; viro@zeniv.linux.org.uk; linux-kernel@vger.kernel.org; > quintela@redhat.com; amit.shah@redhat.com; pbonzini@redhat.com; > dgilbert@redhat.com; linux-mm@kvack.org; kvm@vger.kernel.org; qemu- > devel@nongnu.org; agraf@suse.de; borntraeger@de.ibm.com > Subject: Re: [PATCH kernel 1/2] mm: add the related functions to build the > free page bitmap > > On Tue, Apr 19, 2016 at 03:02:09PM +0000, Li, Liang Z wrote: > > > On Tue, 2016-04-19 at 22:34 +0800, Liang Li wrote: > > > > The free page bitmap will be sent to QEMU through virtio interface > > > > and used for live migration optimization. > > > > Drop the cache before building the free page bitmap can get more > > > > free pages. Whether dropping the cache is decided by user. > > > > > > > > > > How do you prevent the guest from using those recently-freed pages > > > for something else, between when you build the bitmap and the live > > > migration completes? > > > > Because the dirty page logging is enabled before building the bitmap, > > there is no need to prevent the guest from using the recently-freed > pages ... > > > > Liang > > Well one point of telling host that page is free is so that it can mark it clean > even if it was dirty previously. > So I think you must pass the pages to guest under the lock. Thanks! You mean save the free page bitmap in host pages? > This will allow host optimizations such as marking these pages > MADV_DONTNEED or MADV_FREE > Otherwise it's all too tied up to a specific usecase - you aren't telling host that > a page is free, you are telling it that a page was free in the past. > Then we should prevent the guest from using those recently-freed pages, before doing the MADV_DONTNEED or MADV_FREE, or the pages in the free page bitmap may be not free any more. In which case we will do something like this? Balloon? Liang > -- > MST