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,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 90A13C63798 for ; Wed, 25 Nov 2020 05:34:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 307002075A for ; Wed, 25 Nov 2020 05:34:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="SGaaVSxh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727353AbgKYFex (ORCPT ); Wed, 25 Nov 2020 00:34:53 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55215 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725838AbgKYFew (ORCPT ); Wed, 25 Nov 2020 00:34:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606282490; 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: in-reply-to:in-reply-to:references:references; bh=GNqLq5IgMWxaEWp8OZVqcpNyoWNMeYbZubfDbWjaeAE=; b=SGaaVSxhn6FQ2qiURYr/Q6tE9y+SI/qV1TmDo+SyQE/quBDnSpoKWWHyXgtYrYweVHaFW2 JXrWfovRNifjO1mdyA9FeASY8oV1WODNUd3sGG+8VzIjp1rSRKm7ab+W+xNZCGY2z/sAk9 lBTbxIJVN0+8UkAlqoa/2bVC3GumiyQ= 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-225-PcmZFbNHPPi7CxE0Pj9NPQ-1; Wed, 25 Nov 2020 00:34:48 -0500 X-MC-Unique: PcmZFbNHPPi7CxE0Pj9NPQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 63D4E180E46E; Wed, 25 Nov 2020 05:34:46 +0000 (UTC) Received: from mail (ovpn-112-118.rdu2.redhat.com [10.10.112.118]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EEDC060BE5; Wed, 25 Nov 2020 05:34:41 +0000 (UTC) Date: Wed, 25 Nov 2020 00:34:41 -0500 From: Andrea Arcangeli To: Vlastimil Babka , David Hildenbrand Cc: Mel Gorman , Andrew Morton , linux-mm@kvack.org, Qian Cai , Michal Hocko , 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: References: <8C537EB7-85EE-4DCF-943E-3CC0ED0DF56D@lca.pw> <20201121194506.13464-1-aarcange@redhat.com> <20201121194506.13464-2-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.0.2 (2020-11-20) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Mon, Nov 23, 2020 at 02:01:16PM +0100, Vlastimil Babka wrote: > On 11/21/20 8:45 PM, Andrea Arcangeli wrote: > > A corollary issue was fixed in > > 39639000-39814fff : Unknown E820 type > > > > pfn 0x7a200 -> 0x7a200000 min_pfn hit non-RAM: > > > > 7a17b000-7a216fff : Unknown E820 type > > It would be nice to also provide a /proc/zoneinfo and how exactly the > "zone_spans_pfn" was violated. I assume we end up below zone's > start_pfn, but is it true? Agreed, I was about to grab that info along with all page struct around the pfn 0x7a200 and phys address 0x7a216fff. # grep -A1 E820 /proc/iomem 7a17b000-7a216fff : Unknown E820 type 7a217000-7bffffff : System RAM DMA zone_start_pfn 1 zone_end_pfn() 4096 contiguous 1 DMA32 zone_start_pfn 4096 zone_end_pfn() 1048576 contiguous 0 Normal zone_start_pfn 1048576 zone_end_pfn() 4715392 contiguous 1 Movable zone_start_pfn 0 zone_end_pfn() 0 contiguous 0 500222 0x7a1fe000 0x1fff000000001000 reserved True 500223 0x7a1ff000 0x1fff000000001000 reserved True # I suspect "highest pfn" was somewhere in the RAM range # 0x7a217000-0x7a400000 and the pageblock_start_pfn(pfn) # made highest point to pfn 0x7a200 physaddr 0x7a200000 # below, which is reserved indeed since it's non-RAM # first number is pfn hex(500224) == 0x7a200 pfn physaddr page->flags 500224 0x7a200000 0x1fff000000001000 reserved True 500225 0x7a201000 0x1fff000000001000 reserved True *snip* 500245 0x7a215000 0x1fff000000001000 reserved True 500246 0x7a216000 0x1fff000000001000 reserved True 500247 0x7a217000 0x3fff000000000000 reserved False 500248 0x7a218000 0x3fff000000000000 reserved False All RAM pages non-reserved are starting at 0x7a217000 as expected. The non-RAM page_zonenum(pfn_to_page(0x7a200)) points to ZONE_DMA and page_zone(page) below was the DMA zone despite the pfn of 0x7a200 is in DMA32. VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page); So the patch I sent earlier should prevent the above BUG_ON by not setting highest to 0x7a200 when pfn is in the phys RAM range 0x7a217000-0x7a400000, because pageblock_pfn_to_page will notice that the zone is the wrong one. if (page_zone(start_page) != zone) return NULL; However the real bug seems that reserved pages have a zero zone_id in the page->flags when it should have the real zone id/nid. The patch I sent earlier to validate highest would only be needed to deal with pfn_valid. 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); Even if it may not be it, at the light of how the reserved page zoneid/nid initialized went wrong, the above line like it's too flakey to stay. It'd be preferable if the pfn_valid fails and the pfn_to_section_nr(pfn) returns an invalid section for the intermediate step. Even better memset 0xff over the whole page struct until the second stage comes around. 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. Maybe it's not the above that left a zero zoneid though, I haven't tried to bisect it yet to look how the page->flags looked like on a older kernel that didn't seem to reproduce this crash, I'm just guessing. Thanks, Andrea