From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f200.google.com (mail-pf1-f200.google.com [209.85.210.200]) by kanga.kvack.org (Postfix) with ESMTP id 124506B0006 for ; Mon, 6 Aug 2018 16:48:44 -0400 (EDT) Received: by mail-pf1-f200.google.com with SMTP id g18-v6so9191274pfh.20 for ; Mon, 06 Aug 2018 13:48:44 -0700 (PDT) Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com. [115.124.30.131]) by mx.google.com with ESMTPS id q16-v6si10615623pls.404.2018.08.06.13.48.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 06 Aug 2018 13:48:42 -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> From: Yang Shi Message-ID: <28de768b-c740-37b3-ea5a-8e2cb07d2bdc@linux.alibaba.com> Date: Mon, 6 Aug 2018 13:48:35 -0700 MIME-Version: 1.0 In-Reply-To: <20180806204119.GL10003@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 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.