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 58351C5CFE7 for ; Wed, 11 Jul 2018 11:58:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0D315208E5 for ; Wed, 11 Jul 2018 11:58:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0D315208E5 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 S1732527AbeGKMCZ (ORCPT ); Wed, 11 Jul 2018 08:02:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:59136 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726450AbeGKMCZ (ORCPT ); Wed, 11 Jul 2018 08:02:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 31F81ADBE; Wed, 11 Jul 2018 11:58:25 +0000 (UTC) Date: Wed, 11 Jul 2018 13:58:24 +0200 From: Michal Hocko To: "Kirill A. Shutemov" Cc: Yang Shi , willy@infradead.org, ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC v4 0/3] mm: zap pages with read mmap_sem in munmap for large mapping Message-ID: <20180711115824.GN20050@dhcp22.suse.cz> References: <1531265649-93433-1-git-send-email-yang.shi@linux.alibaba.com> <20180711111052.hbyukcwetmjjpij2@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180711111052.hbyukcwetmjjpij2@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 Wed 11-07-18 14:10:52, Kirill A. Shutemov wrote: [...] > It's okay. I have another suggestion that also doesn't require VM_DEAD > trick too :) > > 1. Take mmap_sem for write; > 2. Adjust VMA layout (split/remove). After the step all memory we try to > unmap is outside any VMA. > 3. Downgrade mmap_sem to read. > 4. Zap the page range. > 5. Drop mmap_sem. > > I believe it should be safe. > > The pages in the range cannot be re-faulted after step 3 as find_vma() > will not see the corresponding VMA and deliver SIGSEGV. > > New VMAs cannot be created in the range before step 5 since we hold the > semaphore at least for read the whole time. > > Do you see problem in this approach? Yes this seems to be safe. At least from the first glance. -- Michal Hocko SUSE Labs