From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751574AbdBWT2c (ORCPT ); Thu, 23 Feb 2017 14:28:32 -0500 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:37243 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751107AbdBWT2a (ORCPT ); Thu, 23 Feb 2017 14:28:30 -0500 Date: Thu, 23 Feb 2017 11:04:46 -0800 From: Shaohua Li To: Johannes Weiner CC: , , , , , , , , Subject: Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE list Message-ID: <20170223190446.GA32825@shli-mbp.local> References: <20170223155827.GB4031@cmpxchg.org> <20170223162601.GA18526@brenorobert-mbp.dhcp.thefacebook.com> <20170223182206.GA5686@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20170223182206.GA5686@cmpxchg.org> User-Agent: Mutt/1.6.1 (2016-04-27) X-Originating-IP: [2620:10d:c090:200::5:2185] X-ClientProxiedBy: DM5PR2201CA0056.namprd22.prod.outlook.com (10.174.180.173) To CY4PR15MB1638.namprd15.prod.outlook.com (10.175.119.151) X-MS-Office365-Filtering-Correlation-Id: 3c3890b4-cf13-4e89-f9a1-08d45c1edd8b X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001);SRVR:CY4PR15MB1638; 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> > > > > > > > del_page_from_lru_list(page, lruvec, lru); > > > > + if (PageAnon(page) && !PageSwapBacked(page)) { > > > > + SetPageSwapBacked(page); > > > > + /* charge to anon scanned/rotated reclaim_stat */ > > > > + file = 0; > > > > + lru = LRU_INACTIVE_ANON; > > > > + } > > > > > > As per my previous feedback, please remove this. Write-after-free will > > > be caught and handled in the reclaimer, read-after-free is a bug that > > > really doesn't require optimizing page aging for. And we definitely > > > shouldn't declare invalid data suddenly valid because it's being read. > > > > GUP could run into this. Don't we move the page because it's hot? I think it's > > not just about page aging. If we leave the page there, page reclaim will just > > waste time to reclaim the pages which should't be reclaimed. > > There is just no convincing justification to add this code, because it > optimizes something that doesn't have a real world application. If we > just delete this branch, for all intents and purposes the outcome will > be perfectly acceptable. Ok, looks you want to ignore all corner cases, the gup case is one and the unmap failure and mlock case we discussed before are another. I don't disagree with the intention, but I had the feeling those code will eventually come back. Anyway, I'll delete this code in next post. Thanks, Shaohua