From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f71.google.com (mail-pa0-f71.google.com [209.85.220.71]) by kanga.kvack.org (Postfix) with ESMTP id B02756B007E for ; Tue, 19 Apr 2016 21:41:38 -0400 (EDT) Received: by mail-pa0-f71.google.com with SMTP id zy2so44644846pac.1 for ; Tue, 19 Apr 2016 18:41:38 -0700 (PDT) Received: from mga04.intel.com (mga04.intel.com. [192.55.52.120]) by mx.google.com with ESMTP id p73si14727309pfj.140.2016.04.19.18.41.28 for ; Tue, 19 Apr 2016 18:41:29 -0700 (PDT) From: "Li, Liang Z" Subject: RE: [PATCH kernel 1/2] mm: add the related functions to build the free page bitmap 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> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: 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" > 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 th= e > free page bitmap >=20 > 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 >=20 > Well one point of telling host that page is free is so that it can mark i= t 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. >=20 Then we should prevent the guest from using those recently-freed pages,=20 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 somethi= ng like this? Balloon? Liang > -- > MST -- 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/ . Don't email: email@kvack.org