From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753293AbdCAVRn (ORCPT ); Wed, 1 Mar 2017 16:17:43 -0500 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:55077 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751495AbdCAVRh (ORCPT ); Wed, 1 Mar 2017 16:17:37 -0500 Authentication-Results: kernel.org; dkim=none (message not signed) header.d=none;kernel.org; dmarc=none action=none header.from=fb.com; Date: Wed, 1 Mar 2017 10:18:10 -0800 From: Shaohua Li To: Michal Hocko CC: , , , , , , , , Subject: Re: [PATCH V5 6/6] proc: show MADV_FREE pages info in smaps Message-ID: <20170301181809.GA17275@shli-mbp.local> References: <89efde633559de1ec07444f2ef0f4963a97a2ce8.1487965799.git.shli@fb.com> <20170301133624.GF1124@dhcp22.suse.cz> <20170301173710.GA12867@shli-mbp.local> <20170301174955.GB20360@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20170301174955.GB20360@dhcp22.suse.cz> User-Agent: Mutt/1.6.1 (2016-04-27) X-Originating-IP: [2620:10d:c090:200::3bf0] X-ClientProxiedBy: DM5PR2201CA0047.namprd22.prod.outlook.com (10.174.180.164) To MWHPR15MB1646.namprd15.prod.outlook.com (10.175.138.23) X-MS-Office365-Filtering-Correlation-Id: 0192d36f-9e48-4c5e-8e86-08d460cf5961 X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001);SRVR:MWHPR15MB1646; 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The interface is for > > > > diganose or monitoring purpose, userspace could use it to understand > > > > what happens in the application. Since userspace could dirty MADV_FREE > > > > pages without notice from kernel, this interface is the only place we > > > > can get accurate accounting info about MADV_FREE pages. > > > > > > I have just got to test this patchset and noticed something that was a > > > bit surprising > > > > > > madvise(mmap(len), len, MADV_FREE) > > > Size: 102400 kB > > > Rss: 102400 kB > > > Pss: 102400 kB > > > Shared_Clean: 0 kB > > > Shared_Dirty: 0 kB > > > Private_Clean: 102400 kB > > > Private_Dirty: 0 kB > > > Referenced: 0 kB > > > Anonymous: 102400 kB > > > LazyFree: 102368 kB > > > > > > It took me a some time to realize that LazyFree is not accurate because > > > there are still pages on the per-cpu lru_lazyfree_pvecs. I believe this > > > is an implementation detail which shouldn't be visible to the userspace. > > > Should we simply drain the pagevec? A crude way would be to simply > > > lru_add_drain_all after we are done with the given range. We can also > > > make this lru_lazyfree_pvecs specific but I am not sure this is worth > > > the additional code. > > > > Minchan's original patch includes a drain of pvec. I discard it because I think > > it's not worth the effort. There aren't too many memory in the per-cpu vecs. > > but multiply that by the number of CPUs. > > > Like what you said, I doubt this is noticeable to userspace. > > maybe I wasn't clear enough. I've noticed and I expect others would as > well. We really shouldn't leak implementation details like that. So I > _believe_ this should be fixed. Draining all pagevecs is rather coarse > but it is the simplest thing to do. If you do not want to fold this > into the original patch I can send a standalone one. Or do you have any > concerns about draining? No, no objection at all. Just doubt it's worthy. Looks nobody complains similar issue, For exmaple, deactivate_file_page does the similar thing, then the smaps 'Referenced' could be inaccurate. Thanks, Shaohua