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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 05EDFC77B60 for ; Fri, 28 Apr 2023 11:07:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345690AbjD1LHd (ORCPT ); Fri, 28 Apr 2023 07:07:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345398AbjD1LHb (ORCPT ); Fri, 28 Apr 2023 07:07:31 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E6B87448C for ; Fri, 28 Apr 2023 04:07:29 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 856CF2005F; Fri, 28 Apr 2023 11:07:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1682680048; h=from:from:reply-to: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=Ow3aw4xOvVLC6jge2IF3IgMxcgiXds6JLxSLB6q5HcY=; b=ANKTYutrVBEqWMZ9swOBzcpO+F6v3VRWJC1kQxIr/LVvQP0QCuY9D3iPITCsOaBFWNZZFK xrQ5XqTmePAdS/VRHMDhFOc+a4W4wNPP41J9/qLBapFguH8ljQYPlbAnZ44ibKfGPnJj11 YG0OfLhuROKznSSfMhFBRuxiDn8kqCY= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 75289138FA; Fri, 28 Apr 2023 11:07:28 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id PRjDG/CoS2SBTgAAMHmgww (envelope-from ); Fri, 28 Apr 2023 11:07:28 +0000 Date: Fri, 28 Apr 2023 13:07:28 +0200 From: Michal Hocko To: Yajun Deng Cc: david@redhat.com, osalvador@suse.de, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memory_hotplug: fix dead loop in offline_pages() Message-ID: References: <20230428100846.95535-1-yajun.deng@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230428100846.95535-1-yajun.deng@linux.dev> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 28-04-23 18:08:46, Yajun Deng wrote: > When migration failure in do_migrate_range() and then the > scan_movable_pages() will most likely return the same movable pfn. > In this case, there is no condition to bail out, they will > always run like this: > > ... > [878020.623959] migrating pfn 1727813 failed ret:1 > [878020.623960] page:00000000faa9673c refcount:3 mapcount:0 mapping:00000000144ccd79 index:0x14280025 pfn:0x1727813 > [878020.623962] memcg:ffffa0ff82d5a000 > [878020.623962] aops:def_blk_aops ino:fd00001 > [878020.623964] flags: 0x17ffffc000206a(referenced|dirty|active|workingset|private|node=0|zone=2|lastcpupid=0x1fffff) > [878020.623966] raw: 0017ffffc000206a ffffb0d14f50fbd8 ffffb0d14f50fbd8 ffffa0ff9c155018 > [878020.623967] raw: 0000000014280025 ffffa10327d702d8 00000003ffffffff ffffa0ff82d5a000 > [878020.623968] page dumped because: migration failure > [878020.626196] migrating pfn 1727813 failed ret:1 > [878020.626198] page:00000000faa9673c refcount:3 mapcount:0 mapping:00000000144ccd79 index:0x14280025 pfn:0x1727813 > [878020.626200] memcg:ffffa0ff82d5a000 > [878020.626200] aops:def_blk_aops ino:fd00001 > [878020.626202] flags: 0x17ffffc000206a(referenced|dirty|active|workingset|private|node=0|zone=2|lastcpupid=0x1fffff) > [878020.626204] raw: 0017ffffc000206a ffffb0d14f50fbd8 ffffb0d14f50fbd8 ffffa0ff9c155018 > [878020.626205] raw: 0000000014280025 ffffa10327d702d8 00000003ffffffff ffffa0ff82d5a000 > [878020.626206] page dumped because: migration failure > ... > > Bail out when migration failures reach 3 times. > > Fixes: bb8965bd82fd ("mm, memory_hotplug: deobfuscate migration part of offlining") > Signed-off-by: Yajun Deng Any hard coded failure retry limit will lead to premature failures. Have a look at 72b39cfc4d75 ("mm, memory_hotplug: do not fail offlining too early"). A proper way to deal with this is to implement termination from the userspace (e.g. timeout $TIMEOUT /bin/echo 0 > $PATH_TO_MEM/online) Nacked-by: Michal Hocko > --- > mm/memory_hotplug.c | 19 ++++++++++++++----- > 1 file changed, 14 insertions(+), 5 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 8e0fa209d533..72dd385b8892 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1800,11 +1800,12 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages, > struct zone *zone, struct memory_group *group) > { > const unsigned long end_pfn = start_pfn + nr_pages; > - unsigned long pfn, system_ram_pages = 0; > + unsigned long pfn, tmp_pfn, system_ram_pages = 0; > const int node = zone_to_nid(zone); > unsigned long flags; > struct memory_notify arg; > char *reason; > + int count = 0; > int ret; > > /* > @@ -1887,12 +1888,20 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages, > > cond_resched(); > > + tmp_pfn = pfn; > ret = scan_movable_pages(pfn, end_pfn, &pfn); > if (!ret) { > - /* > - * TODO: fatal migration failures should bail > - * out > - */ > + if (pfn == tmp_pfn) > + count++; > + else > + count = 0; > + > + if (unlikely(count == 3)) { > + ret = -EBUSY; > + reason = "migration failure"; > + goto failed_removal_isolated; > + } > + > do_migrate_range(pfn, end_pfn); > } > } while (!ret); > -- > 2.25.1 -- Michal Hocko SUSE Labs