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 33829C5519F for ; Wed, 25 Nov 2020 13:41:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0F9F206D8 for ; Wed, 25 Nov 2020 13:41:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YUS1+g3J" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729338AbgKYNlS (ORCPT ); Wed, 25 Nov 2020 08:41:18 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:57519 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726162AbgKYNlS (ORCPT ); Wed, 25 Nov 2020 08:41:18 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606311676; 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=2CSJkwJ01yCXtKhyXjj7mNDHOXO25ExUWkF5Tdyq0h0=; b=YUS1+g3J6CBkOjacVm3mzgNp075DjHVs1ejVQfF8CswRugj+kVdYUzQO9X/RY7Fok72qKU 0/+mNxwdGytuWm8iSLjtT6KLj3PlZ4BREHPghmagcoGGGxl4PTYJzE9TSewjA+cNjHYWb1 Cn8v+UinJcl3xvsfQARMMKUPVvkP6es= 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-548-06i0NvPvMl2IWapNuFFuAw-1; Wed, 25 Nov 2020 08:41:14 -0500 X-MC-Unique: 06i0NvPvMl2IWapNuFFuAw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 42D049A234; Wed, 25 Nov 2020 13:41:13 +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 65D6C60854; Wed, 25 Nov 2020 13:41:11 +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> <5f01bde6-fe31-9b0e-f288-06b82598a8b3@redhat.com> <20201125133346.GN3306@suse.de> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Wed, 25 Nov 2020 14:41:10 +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: <20201125133346.GN3306@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 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.11.20 14:33, Mel Gorman wrote: > On Wed, Nov 25, 2020 at 12:04:15PM +0100, David Hildenbrand wrote: >> 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? >> > > It can also occur in the middle of the zone. > >> 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? > > Assuming a hole is not MAX_ORDER-aligned but there is real memory within > the page block, then the node/zone for the struct pages backing the hole > should match the real memorys node and zone. > > As it stands, with the uninitialised node/zone, certain checks like > page_is_buddy(): page_zone_id(page) != page_zone_id(buddy) may only > work by co-incidence. page_is_buddy() happens to work anyway because > PageBuddy(buddy) would never be true for a PageReserved page. > >> With >> memory hotplug after such a hole, we can easily have multiple >> nodes/zones spanning such a hole, unknown before hotplug. >> > > When hotplugged, the same logic would apply. Where the hole is not aligned, > the struct page linkages should match the "real" memory". > >>> 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. >> > > I think it'll be ok as long as the struct pages within a 1<<(MAX_ORDER-1) > range have proper linkages. Agreed. -- Thanks, David / dhildenb