From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E55FC43140 for ; Wed, 20 Jun 2018 16:23:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E5F882083A for ; Wed, 20 Jun 2018 16:23:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E5F882083A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754378AbeFTQXg (ORCPT ); Wed, 20 Jun 2018 12:23:36 -0400 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:48500 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754065AbeFTQXf (ORCPT ); Wed, 20 Jun 2018 12:23:35 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04446;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0T33Bl7A_1529511799; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0T33Bl7A_1529511799) by smtp.aliyun-inc.com(127.0.0.1); Thu, 21 Jun 2018 00:23:26 +0800 Subject: Re: [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping To: Michal Hocko Cc: Peter Zijlstra , willy@infradead.org, ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1529364856-49589-1-git-send-email-yang.shi@linux.alibaba.com> <1529364856-49589-3-git-send-email-yang.shi@linux.alibaba.com> <20180619100218.GN2458@hirez.programming.kicks-ass.net> <20180620071708.GI13685@dhcp22.suse.cz> From: Yang Shi Message-ID: <41456a0f-0091-dfdb-952b-9bf08b323ba6@linux.alibaba.com> Date: Wed, 20 Jun 2018 09:23:17 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180620071708.GI13685@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/20/18 12:17 AM, Michal Hocko wrote: > On Tue 19-06-18 14:13:05, Yang Shi wrote: >> >> On 6/19/18 3:02 AM, Peter Zijlstra wrote: > [...] >>> Hold up, two things: you having to copy most of do_munmap() didn't seem >>> to suggest a helper function? And second, since when are we allowed to >> Yes, they will be extracted into a helper function in the next version. >> >> May bad, I don't think it is allowed. We could reform this to: >> >> acquire write mmap_sem >> vma lookup (split vmas) >> release write mmap_sem >> >> acquire read mmap_sem >> zap pages >> release read mmap_sem >> >> I'm supposed this is safe as what Michal said before. > I didn't get to read your patches carefully yet but I am wondering why > do you need to split in the first place. Why cannot you simply unmap the > range (madvise(DONTNEED)) under the read lock and then take the lock for > write to finish the rest? Yes, we can. I just thought splitting vma up-front sounds more straight forward. But, I neglected the write mmap_sem issue. Will move the vma split into later write mmap_sem in the next version. Thanks, Yang