From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47119) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xrid4-0005xa-TN for qemu-devel@nongnu.org; Fri, 21 Nov 2014 02:27:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xricy-00017S-MH for qemu-devel@nongnu.org; Fri, 21 Nov 2014 02:27:42 -0500 Received: from szxga01-in.huawei.com ([119.145.14.64]:62780) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xricy-000151-1b for qemu-devel@nongnu.org; Fri, 21 Nov 2014 02:27:36 -0500 Message-ID: <546EE780.8070307@huawei.com> Date: Fri, 21 Nov 2014 15:19:28 +0800 From: zhanghailiang MIME-Version: 1.0 References: <1412356087-16115-1-git-send-email-aarcange@redhat.com> <544E1143.1080905@huawei.com> <20141029174607.GK19606@redhat.com> <545221A4.9030606@huawei.com> <20141030124950.GJ2376@work-vm> <5452E531.4070205@huawei.com> <20141119184938.GE803@redhat.com> <546D57E5.3080803@huawei.com> <20141120173833.GG803@redhat.com> In-Reply-To: <20141120173833.GG803@redhat.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 00/17] RFC: userfault v2 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Arcangeli Cc: Robert Love , Dave Hansen , Jan Kara , kvm@vger.kernel.org, Neil Brown , Stefan Hajnoczi , qemu-devel@nongnu.org, KOSAKI Motohiro , Michel Lespinasse , Taras Glek , Andrew Jones , Juan Quintela , Hugh Dickins , Isaku Yamahata , Mel Gorman , Sasha Levin , Android Kernel Team , "Dr. David Alan Gilbert" , "Huangpeng (Peter)" , Andres Lagar-Cavilla , Christopher Covington , Anthony Liguori , Paolo Bonzini , Keith Packard , Wenchao Xia , linux-kernel@vger.kernel.org, Andy Lutomirski , Minchan Kim , Dmitry Adamushko , Johannes Weiner , Mike Hommey , Andrew Morton , Peter Feiner On 2014/11/21 1:38, Andrea Arcangeli wrote: > Hi, > > On Thu, Nov 20, 2014 at 10:54:29AM +0800, zhanghailiang wrote: >> Yes, you are right. This is what i really want, bypass all non-present faults >> and only track strict wrprotect faults. ;) >> >> So, do you plan to support that in the userfault API? > > Yes I think it's good idea to support wrprotect/COW faults too. > Great! Then i can expect your patches. ;) > I just wanted to understand if there was any other reason why you > needed only wrprotect faults, because the non-present faults didn't > look like a big performance concern if they triggered in addition to > wrprotect faults, but it's certainly ok to optimize them away so it's > fully optimal. > Er, you have got the answer, no special, it's only for optimality. > All it takes to differentiate the behavior should be one more bit > during registration so you can select non-present, wrprotect faults or > both. postcopy live migration would select only non-present faults, > postcopy live snapshot would select only wrprotect faults, anything > like distributed shared memory supporting shared readonly access and > exclusive write access, would select both flags. > It is really flexible in this way. > I just sent an (unfortunately) longish but way more detailed email > about live snapshotting with userfaultfd but I just wanted to give a > shorter answer here too :). > Thanks for your explanation, and your patience. It is really useful, now i know more details about why 'fork & dump live snapshot' scenario is not acceptable. Thanks :) > Thanks, > Andrea > > . >