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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED 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 A68D2C3279B for ; Sat, 30 Jun 2018 04:26:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 58E112772F for ; Sat, 30 Jun 2018 04:26:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 58E112772F 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 S932343AbeF3E0x (ORCPT ); Sat, 30 Jun 2018 00:26:53 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:35388 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932137AbeF3E0w (ORCPT ); Sat, 30 Jun 2018 00:26:52 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04455;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=15;SR=0;TI=SMTPD_---0T3eli3V_1530332784; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0T3eli3V_1530332784) by smtp.aliyun-inc.com(127.0.0.1); Sat, 30 Jun 2018 12:26:29 +0800 Subject: Re: [RFC v3 PATCH 4/5] mm: mmap: zap pages with read mmap_sem for large mapping To: Andrew Morton Cc: mhocko@kernel.org, willy@infradead.org, ldufour@linux.vnet.ibm.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, tglx@linutronix.de, hpa@zytor.com, linux-mm@kvack.org, x86@kernel.org, linux-kernel@vger.kernel.org References: <1530311985-31251-1-git-send-email-yang.shi@linux.alibaba.com> <1530311985-31251-5-git-send-email-yang.shi@linux.alibaba.com> <20180629183501.9e30c26135f11853245c56c7@linux-foundation.org> <084aeccb-2c54-2299-8bf0-29a10cc0186e@linux.alibaba.com> <20180629201547.5322cfc4b52d19a0443daec2@linux-foundation.org> From: Yang Shi Message-ID: Date: Fri, 29 Jun 2018 21:26:23 -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: <20180629201547.5322cfc4b52d19a0443daec2@linux-foundation.org> 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 6/29/18 8:15 PM, Andrew Morton wrote: > On Fri, 29 Jun 2018 19:28:15 -0700 Yang Shi wrote: > >> >>> we're adding a bunch of code to 32-bit kernels which will never be >>> executed. >>> >>> I'm thinking it would be better to be much more explicit with "#ifdef >>> CONFIG_64BIT" in this code, rather than relying upon the above magic. >>> >>> But I tend to think that the fact that we haven't solved anything on >>> locked vmas or on uprobed mappings is a shostopper for the whole >>> approach :( >> I agree it is not that perfect. But, it still could improve the most use >> cases. > Well, those unaddressed usecases will need to be fixed at some point. Yes, definitely. > What's our plan for that? As I mentioned in the earlier email, locked and hugetlb cases might be able to be solved by separating vm_flags update and actual unmap. I will look into it further later. From my point of view, uprobe mapping sounds not that vital. > > Would one of your earlier designs have addressed all usecases? I > expect the dumb unmap-a-little-bit-at-a-time approach would have? Yes. The v1 design does unmap with holding write map_sem. So, the vm_flags update is not a problem. Thanks, Yang > >> For the locked vmas and hugetlb vmas, unmapping operations need modify >> vm_flags. But, I'm wondering we might be able to separate unmap and >> vm_flags update. Because we know they will be unmapped right away, the >> vm_flags might be able to be updated in write mmap_sem critical section >> before the actual unmap is called or after it. This is just off the top >> of my head. >> >> For uprobed mappings, I'm not sure how vital it is to this case. >> >> Thanks, >> Yang >>