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 77341C433F4 for ; Wed, 29 Aug 2018 18:39:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 22567204FD for ; Wed, 29 Aug 2018 18:39:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 22567204FD 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 S1728418AbeH2WhU (ORCPT ); Wed, 29 Aug 2018 18:37:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:55094 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727657AbeH2WhT (ORCPT ); Wed, 29 Aug 2018 18:37:19 -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 10D66AB64; Wed, 29 Aug 2018 18:39:08 +0000 (UTC) Date: Wed, 29 Aug 2018 20:39:06 +0200 From: Michal Hocko To: Jerome Glisse Cc: Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A . Shutemov" , Vlastimil Babka , Naoya Horiguchi , Davidlohr Bueso , Andrew Morton , stable@vger.kernel.org Subject: Re: [PATCH v6 1/2] mm: migration: fix migration of huge PMD shared pages Message-ID: <20180829183906.GF10223@dhcp22.suse.cz> References: <20180823205917.16297-1-mike.kravetz@oracle.com> <20180823205917.16297-2-mike.kravetz@oracle.com> <20180824084157.GD29735@dhcp22.suse.cz> <6063f215-a5c8-2f0c-465a-2c515ddc952d@oracle.com> <20180827074645.GB21556@dhcp22.suse.cz> <20180827134633.GB3930@redhat.com> <9209043d-3240-105b-72a3-b4cd30f1b1f1@oracle.com> <20180829181424.GB3784@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180829181424.GB3784@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 29-08-18 14:14:25, Jerome Glisse wrote: > On Wed, Aug 29, 2018 at 10:24:44AM -0700, Mike Kravetz wrote: [...] > > What would be the best mmu notifier interface to use where there are no > > start/end calls? > > Or, is the best solution to add the start/end calls as is done in later > > versions of the code? If that is the suggestion, has there been any change > > in invalidate start/end semantics that we should take into account? > > start/end would be the one to add, 4.4 seems broken in respect to THP > and mmu notification. Another solution is to fix user of mmu notifier, > they were only a handful back then. For instance properly adjust the > address to match first address covered by pmd or pud and passing down > correct page size to mmu_notifier_invalidate_page() would allow to fix > this easily. > > This is ok because user of try_to_unmap_one() replace the pte/pmd/pud > with an invalid one (either poison, migration or swap) inside the > function. So anyone racing would synchronize on those special entry > hence why it is fine to delay mmu_notifier_invalidate_page() to after > dropping the page table lock. > > Adding start/end might the solution with less code churn as you would > only need to change try_to_unmap_one(). What about dependencies? 369ea8242c0fb sounds like it needs work for all notifiers need to be updated as well. Anyway, I am wondering why we haven't see any bugs coming from incomplete range invalidation. How would those exhibit? -- Michal Hocko SUSE Labs