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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 6A51BC3279B for ; Mon, 2 Jul 2018 20:48:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2841325116 for ; Mon, 2 Jul 2018 20:48:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2841325116 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org 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 S1752833AbeGBUsu (ORCPT ); Mon, 2 Jul 2018 16:48:50 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:34592 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752537AbeGBUst (ORCPT ); Mon, 2 Jul 2018 16:48:49 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.9.92]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 9EC5FCFC; Mon, 2 Jul 2018 20:48:48 +0000 (UTC) Date: Mon, 2 Jul 2018 13:48:45 -0700 From: Andrew Morton To: Michal Hocko Cc: Yang Shi , 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 Subject: Re: [RFC v3 PATCH 4/5] mm: mmap: zap pages with read mmap_sem for large mapping Message-Id: <20180702134845.c4f536dead5374b443e24270@linux-foundation.org> In-Reply-To: <20180702140502.GZ19043@dhcp22.suse.cz> 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> <20180702140502.GZ19043@dhcp22.suse.cz> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2 Jul 2018 16:05:02 +0200 Michal Hocko wrote: > On Fri 29-06-18 20:15:47, Andrew Morton wrote: > [...] > > Would one of your earlier designs have addressed all usecases? I > > expect the dumb unmap-a-little-bit-at-a-time approach would have? > > It has been already pointed out that this will not work. I said "one of". There were others. > You simply > cannot drop the mmap_sem during unmap because another thread could > change the address space under your feet. So you need some form of > VM_DEAD and handle concurrent and conflicting address space operations. Unclear that this is a problem. If a thread does an unmap of a range of virtual address space, there's no guarantee that upon return some other thread has not already mapped new stuff into that address range. So what's changed?