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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 32DC1C5519F for ; Wed, 25 Nov 2020 11:04:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CB60A20857 for ; Wed, 25 Nov 2020 11:04:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="fON0q246" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727341AbgKYLEZ (ORCPT ); Wed, 25 Nov 2020 06:04:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:44320 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725792AbgKYLEZ (ORCPT ); Wed, 25 Nov 2020 06:04:25 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606302263; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ko+UcIV0NRJ5DII8yo9h6rReKOOqZlMAZOJv2cY0hjc=; b=fON0q246baRA6v8+w3wgH9a0o0ip7byK4RYx4UyD+ooNuSOn1Nosp78eEg6D2rr/twNWFG APxJk/0fd2xkGl848yvi8uFPMPvnxp6MZJnMxtir5P76ldTGPL4MGehweYXSy93yna5th8 26hhG//Q3m/pQgfGe5nUaRfa05PeRl0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-446-sUaslyR0N2SMilzQfgdObA-1; Wed, 25 Nov 2020 06:04:19 -0500 X-MC-Unique: sUaslyR0N2SMilzQfgdObA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 537001006C90; Wed, 25 Nov 2020 11:04:18 +0000 (UTC) Received: from [10.36.112.131] (ovpn-112-131.ams2.redhat.com [10.36.112.131]) by smtp.corp.redhat.com (Postfix) with ESMTP id 18B745C1A3; Wed, 25 Nov 2020 11:04:15 +0000 (UTC) Subject: Re: [PATCH 1/1] mm: compaction: avoid fast_isolate_around() to set pageblock_skip on reserved pages To: Mel Gorman Cc: Andrea Arcangeli , Vlastimil Babka , Andrew Morton , linux-mm@kvack.org, Qian Cai , Michal Hocko , linux-kernel@vger.kernel.org, Mike Rapoport , Baoquan He References: <35F8AADA-6CAA-4BD6-A4CF-6F29B3F402A4@redhat.com> <20201125103933.GM3306@suse.de> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <5f01bde6-fe31-9b0e-f288-06b82598a8b3@redhat.com> Date: Wed, 25 Nov 2020 12:04:15 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201125103933.GM3306@suse.de> Content-Type: text/plain; charset=iso-8859-15 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.11.20 11:39, Mel Gorman wrote: > On Wed, Nov 25, 2020 at 07:45:30AM +0100, David Hildenbrand wrote: >>> Something must have changed more recently than v5.1 that caused the >>> zoneid of reserved pages to be wrong, a possible candidate for the >>> real would be this change below: >>> >>> + __init_single_page(pfn_to_page(pfn), pfn, 0, 0); >>> >> >> Before that change, the memmap of memory holes were only zeroed out. So the zones/nid was 0, however, pages were not reserved and had a refcount of zero - resulting in other issues. >> >> Most pfn walkers shouldn???t mess with reserved pages and simply skip them. That would be the right fix here. >> > > Ordinarily yes, pfn walkers should not care about reserved pages but it's > still surprising that the node/zone linkages would be wrong for memory > holes. If they are in the middle of a zone, it means that a hole with > valid struct pages could be mistaken for overlapping nodes (if the hole > was in node 1 for example) or overlapping zones which is just broken. I agree within zones - but AFAIU, the issue is reserved memory between zones, right? Assume your end of memory falls within a section - what would be the right node/zone for such a memory hole at the end of the section? With memory hotplug after such a hole, we can easily have multiple nodes/zones spanning such a hole, unknown before hotplug. IMHO, marking memory holes properly (as discussed) would be the cleanest approach. For now, we use node/zone 0 + PageReserved - because memory hotunplug (zone shrinking etc.) doesn't really care about ZONE_DMA. > >>> >>> Whenever pfn_valid is true, it's better that the zoneid/nid is correct >>> all times, otherwise if the second stage fails we end up in a bug with >>> weird side effects. >> >> Memory holes with a valid memmap might not have a zone/nid. For now, skipping reserved pages should be good enough, no? >> > > It would partially paper over the issue that setting the pageblock type > based on a reserved page. I agree that compaction should not be returning > pfns that are outside of the zone range because that is buggy in itself > but valid struct pages should have valid information. I don't think we > want to paper over that with unnecessary PageReserved checks. Agreed as long as we can handle that issue using range checks. -- Thanks, David / dhildenb