From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f198.google.com (mail-pg1-f198.google.com [209.85.215.198]) by kanga.kvack.org (Postfix) with ESMTP id BB5C66B0007 for ; Tue, 7 Aug 2018 21:52:08 -0400 (EDT) Received: by mail-pg1-f198.google.com with SMTP id x2-v6so307854pgp.4 for ; Tue, 07 Aug 2018 18:52:08 -0700 (PDT) Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com. [115.124.30.132]) by mx.google.com with ESMTPS id u186-v6si2780602pgd.578.2018.08.07.18.52.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 07 Aug 2018 18:52:07 -0700 (PDT) Subject: Re: [RFC v6 PATCH 2/2] mm: mmap: zap pages with read mmap_sem in munmap 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 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: owner-linux-mm@kvack.org List-ID: 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 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.