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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 BD358C63697 for ; Thu, 26 Nov 2020 10:47:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 649042173E for ; Thu, 26 Nov 2020 10:47:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388336AbgKZKrZ (ORCPT ); Thu, 26 Nov 2020 05:47:25 -0500 Received: from mx2.suse.de ([195.135.220.15]:57850 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388289AbgKZKrZ (ORCPT ); Thu, 26 Nov 2020 05:47:25 -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 45855AC2E; Thu, 26 Nov 2020 10:47:23 +0000 (UTC) Date: Thu, 26 Nov 2020 10:47:20 +0000 From: Mel Gorman To: Andrea Arcangeli Cc: Vlastimil Babka , Andrew Morton , linux-mm@kvack.org, Qian Cai , Michal Hocko , David Hildenbrand , linux-kernel@vger.kernel.org, Mike Rapoport , Baoquan He Subject: Re: [PATCH 1/1] mm: compaction: avoid fast_isolate_around() to set pageblock_skip on reserved pages Message-ID: <20201126104720.GO3306@suse.de> References: <8C537EB7-85EE-4DCF-943E-3CC0ED0DF56D@lca.pw> <20201121194506.13464-1-aarcange@redhat.com> <20201121194506.13464-2-aarcange@redhat.com> <20201124133205.GK3306@suse.de> <20201125103053.GL3306@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 25, 2020 at 12:59:58PM -0500, Andrea Arcangeli wrote: > On Wed, Nov 25, 2020 at 10:30:53AM +0000, Mel Gorman wrote: > > On Tue, Nov 24, 2020 at 03:56:22PM -0500, Andrea Arcangeli wrote: > > > Hello, > > > > > > On Tue, Nov 24, 2020 at 01:32:05PM +0000, Mel Gorman wrote: > > > > I would hope that is not the case because they are not meant to overlap. > > > > However, if the beginning of the pageblock was not the start of a zone > > > > then the pages would be valid but the pfn would still be outside the > > > > zone boundary. If it was reserved, the struct page is valid but not > > > > suitable for set_pfnblock_flags_mask. However, it is a concern in > > > > general because the potential is there that pages are isolated from the > > > > wrong zone. > > > > > > I guess we have more than one issue to correct in that function > > > because the same BUG_ON reproduced again even with the tentative patch > > > I posted earlier. > > > > > > So my guess is that the problematic reserved page isn't pointed by the > > > min_pfn, but it must have been pointed by the "highest" variable > > > calculated below? > > > > > > if (pfn >= highest) > > > highest = pageblock_start_pfn(pfn); > > > > > > When I looked at where "highest" comes from, it lacks > > > pageblock_pfn_to_page check (which was added around v5.7 to min_pfn). > > > > > > Is that the real bug, which may be fixed by something like this? (untested) > > > > > > > It's plausible as it is a potential source of leaking but as you note > > in another mail, it's surprising to me that valid struct pages, even if > > within memory holes and reserved would have broken node/zone information > > in the page flags. > > I think the patch to add pageblock_pfn_to_page is still needed to cope > with !pfn_valid or a pageblock in between zones, but pfn_valid or > pageblock in between zones is not what happens here. > > So the patch adding pageblock_pfn_to_page would have had the undesired > side effect of hiding the bug so it's best to deal with the other bug > first. > Agreed. This thread has a lot of different directions in it at this point so what I'd hope for is first, a patch that initialises holes with zone/node linkages within a 1<<(MAX_ORDER-1) alignment. If there is a hole, it would be expected the pages are PageReserved. Second, a fix to fast_isolate that forces PFNs returned to always be within the stated zone boundaries. The first is because there are assumptions that without HOLES_IN_ZONE, a true pfn_valid within 1<<(MAX_ORDER-1) means pfn_valid would be true for any PFN within that range. That assumption is relaxed in many cases -- e.g. the page allocator may not care at the moment because of how it orders checks but compaction assumes that pfn_valid within a pageblock means that all PFNs within that pageblock are valid. -- Mel Gorman SUSE Labs