From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757431AbaKUH1u (ORCPT ); Fri, 21 Nov 2014 02:27:50 -0500 Received: from szxga01-in.huawei.com ([119.145.14.64]:64296 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751079AbaKUH1s (ORCPT ); Fri, 21 Nov 2014 02:27:48 -0500 Message-ID: <546EE780.8070307@huawei.com> Date: Fri, 21 Nov 2014 15:19:28 +0800 From: zhanghailiang User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101 Thunderbird/31.1.1 MIME-Version: 1.0 To: Andrea Arcangeli CC: "Dr. David Alan Gilbert" , , , , Andres Lagar-Cavilla , Dave Hansen , Paolo Bonzini , Rik van Riel , Mel Gorman , Andy Lutomirski , Andrew Morton , Sasha Levin , "Hugh Dickins" , Peter Feiner , "Christopher Covington" , Johannes Weiner , "Android Kernel Team" , Robert Love , "Dmitry Adamushko" , Neil Brown , "Mike Hommey" , Taras Glek , Jan Kara , KOSAKI Motohiro , "Michel Lespinasse" , Minchan Kim , "Keith Packard" , "Huangpeng (Peter)" , Isaku Yamahata , Anthony Liguori , Stefan Hajnoczi , Wenchao Xia , Andrew Jones , Juan Quintela Subject: Re: [PATCH 00/17] RFC: userfault v2 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 X-Originating-IP: [10.177.22.69] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > . >