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=-1.0 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 8E6ACC46471 for ; Mon, 6 Aug 2018 22:19:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 48F8C21A56 for ; Mon, 6 Aug 2018 22:19:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 48F8C21A56 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 S1733188AbeHGAaf (ORCPT ); Mon, 6 Aug 2018 20:30:35 -0400 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:42526 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732106AbeHGAaf (ORCPT ); Mon, 6 Aug 2018 20:30:35 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01353;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0T68SOWV_1533593947; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0T68SOWV_1533593947) by smtp.aliyun-inc.com(127.0.0.1); Tue, 07 Aug 2018 06:19:09 +0800 Subject: Re: [RFC v6 PATCH 2/2] mm: mmap: zap pages with read mmap_sem in munmap To: Michal Hocko Cc: willy@infradead.org, ldufour@linux.vnet.ibm.com, kirill@shutemov.name, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1532628614-111702-1-git-send-email-yang.shi@linux.alibaba.com> <1532628614-111702-3-git-send-email-yang.shi@linux.alibaba.com> <20180803090759.GI27245@dhcp22.suse.cz> <20180806094005.GG19540@dhcp22.suse.cz> <76c0fc2b-fca7-9f22-214a-920ee2537898@linux.alibaba.com> <20180806204119.GL10003@dhcp22.suse.cz> <28de768b-c740-37b3-ea5a-8e2cb07d2bdc@linux.alibaba.com> <20180806205232.GN10003@dhcp22.suse.cz> From: Yang Shi Message-ID: <0cdff13a-2713-c5be-a33e-28c07e093bcc@linux.alibaba.com> Date: Mon, 6 Aug 2018 15:19:06 -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: <20180806205232.GN10003@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 8/6/18 1:52 PM, Michal Hocko wrote: > On Mon 06-08-18 13:48:35, Yang Shi wrote: >> >> On 8/6/18 1:41 PM, Michal Hocko wrote: >>> On Mon 06-08-18 09:46:30, Yang Shi wrote: >>>> On 8/6/18 2:40 AM, Michal Hocko wrote: >>>>> On Fri 03-08-18 14:01:58, Yang Shi wrote: >>>>>> On 8/3/18 2:07 AM, Michal Hocko wrote: >>>>>>> On Fri 27-07-18 02:10:14, Yang Shi wrote: >>> [...] >>>>>>>> If the vma has VM_LOCKED | VM_HUGETLB | VM_PFNMAP or uprobe, they are >>>>>>>> considered as special mappings. They will be dealt with before zapping >>>>>>>> pages with write mmap_sem held. Basically, just update vm_flags. >>>>>>> Well, I think it would be safer to simply fallback to the current >>>>>>> implementation with these mappings and deal with them on top. This would >>>>>>> make potential issues easier to bisect and partial reverts as well. >>>>>> Do you mean just call do_munmap()? It sounds ok. Although we may waste some >>>>>> cycles to repeat what has done, it sounds not too bad since those special >>>>>> mappings should be not very common. >>>>> VM_HUGETLB is quite spread. Especially for DB workloads. >>>> Wait a minute. In this way, it sounds we go back to my old implementation >>>> with special handling for those mappings with write mmap_sem held, right? >>> Yes, I would really start simple and add further enhacements on top. >> If updating vm_flags with read lock is safe in this case, we don't have to >> do this. The only reason for this special handling is about vm_flags update. > > Yes, maybe you are right that this is safe. I would still argue to have > it in a separate patch for easier review, bisectability etc... Sorry, I'm a little bit confused. Do you mean I should have the patch *without* handling the special case (just like to assume it is safe to update vm_flags with read lock), then have the other patch on top of it, which simply calls do_munmap() to deal with the special cases? >