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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 6FC99C433E6 for ; Wed, 17 Feb 2021 12:28:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4896A64E0F for ; Wed, 17 Feb 2021 12:28:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232397AbhBQM2Y (ORCPT ); Wed, 17 Feb 2021 07:28:24 -0500 Received: from mx2.suse.de ([195.135.220.15]:57804 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230473AbhBQM2U (ORCPT ); Wed, 17 Feb 2021 07:28:20 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id C95DAB9D4; Wed, 17 Feb 2021 12:27:38 +0000 (UTC) To: Mike Rapoport Cc: Michal Hocko , Mel Gorman , David Hildenbrand , Andrew Morton , Andrea Arcangeli , Baoquan He , Borislav Petkov , Chris Wilson , "H. Peter Anvin" , Ingo Molnar , Linus Torvalds , =?UTF-8?Q?=c5=81ukasz_Majczak?= , Mike Rapoport , Qian Cai , "Sarvela, Tomi P" , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org References: <20210214180016.GO242749@kernel.org> <20210215212440.GA1307762@kernel.org> <20210216110154.GB1307762@kernel.org> <20210216174914.GD1307762@kernel.org> From: Vlastimil Babka Subject: Re: [PATCH v5 1/1] mm: refactor initialization of struct page for holes in memory layout Message-ID: <0255912b-19af-e8fc-9a04-06a519287716@suse.cz> Date: Wed, 17 Feb 2021 13:27:37 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210216174914.GD1307762@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/16/21 6:49 PM, Mike Rapoport wrote: > Hi Vlastimil, > > On Tue, Feb 16, 2021 at 05:39:12PM +0100, Vlastimil Babka wrote: >> >> >> So, Andrea could you please check if this fixes the original >> fast_isolate_around() issue for you? With the VM_BUG_ON not removed, DEBUG_VM >> enabled, no changes to struct page initialization... >> It relies on pageblock_pfn_to_page as the rest of the compaction code. > > Pardon my ignorance of compaction internals, but does this mean that with > your patch we'll never call set_pfnblock_flags_mask() for a pfn in a hole? No it doesn't mean that kind of guarantee. But we will not call it anymore (if my patch is correct) from a path which we currently know it's doing that and triggering the VM_BUG_ON. So that's a targetted fix that matches stable backport criteria. It doesn't contradict your patch as a way to improve mainline, I still agree it's best long-term if we initialize the struct pages without such surprises. But I also agree with Michal that there's a risk of replacing one corner case with another and thus we shouldn't do that as a stable fix.