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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 03968C3279B for ; Mon, 2 Jul 2018 12:49:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BA61225370 for ; Mon, 2 Jul 2018 12:49:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BA61225370 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.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 S1752186AbeGBMte (ORCPT ); Mon, 2 Jul 2018 08:49:34 -0400 Received: from mx2.suse.de ([195.135.220.15]:34916 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751493AbeGBMtb (ORCPT ); Mon, 2 Jul 2018 08:49:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 47039AF63; Mon, 2 Jul 2018 12:49:30 +0000 (UTC) Date: Mon, 2 Jul 2018 14:49:28 +0200 From: Michal Hocko To: "Kirill A. Shutemov" Cc: Yang Shi , willy@infradead.org, ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org, 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: <20180702124928.GQ19043@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> <20180702123350.dktmzlmztulmtrae@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180702123350.dktmzlmztulmtrae@kshutemo-mobl1> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 02-07-18 15:33:50, Kirill A. Shutemov wrote: [...] > I probably miss the explanation somewhere, but what's wrong with allowing > other thread to re-populate the VMA? We have discussed that earlier and it boils down to how is racy access to munmap supposed to behave. Right now we have either the original content or SEGV. If we allow to simply madvise_dontneed before real unmap we could get a new page as well. There might be (quite broken I would say) user space code that would simply corrupt data silently that way. -- Michal Hocko SUSE Labs