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[209.132.180.67]) by mx.google.com with ESMTP id b28-v6si3045365pfe.265.2018.08.07.18.53.14; Tue, 07 Aug 2018 18:53:28 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=alibaba.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727139AbeHHEJa (ORCPT + 99 others); Wed, 8 Aug 2018 00:09:30 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:37822 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726245AbeHHEJ3 (ORCPT ); Wed, 8 Aug 2018 00:09:29 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01451;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0T6ELMru_1533693108; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0T6ELMru_1533693108) by smtp.aliyun-inc.com(127.0.0.1); Wed, 08 Aug 2018 09:51:55 +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> <0cdff13a-2713-c5be-a33e-28c07e093bcc@linux.alibaba.com> <20180807054524.GQ10003@dhcp22.suse.cz> From: Yang Shi Message-ID: <04a22c49-fe30-63ac-c1b7-46a405c810e2@linux.alibaba.com> Date: Tue, 7 Aug 2018 18:51:45 -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: <20180807054524.GQ10003@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 10:45 PM, Michal Hocko wrote: > On Mon 06-08-18 15:19:06, Yang Shi wrote: >> >> 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? > Just skip those special cases in the initial implementation and handle > each special case in its own patch on top. Thanks. VM_LOCKED area will not be handled specially since it is easy to handle it, just follow what do_munmap does. The special cases will just handle VM_HUGETLB, VM_PFNMAP and uprobe mappings.