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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 632B513F6DFF for ; Mon, 30 Jul 2018 09:16:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1874120873 for ; Mon, 30 Jul 2018 09:16:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1874120873 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726743AbeG3KuK (ORCPT ); Mon, 30 Jul 2018 06:50:10 -0400 Received: from mx2.suse.de ([195.135.220.15]:38070 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726686AbeG3KuK (ORCPT ); Mon, 30 Jul 2018 06:50:10 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 767C4AE08; Mon, 30 Jul 2018 09:16:06 +0000 (UTC) Date: Mon, 30 Jul 2018 11:16:05 +0200 From: Michal Hocko To: John Allen Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kamezawa.hiroyu@jp.fujitsu.com, n-horiguchi@ah.jp.nec.com, mgorman@suse.de, nfont@linux.vnet.ibm.com Subject: Re: Infinite looping observed in __offline_pages Message-ID: <20180730091605.GF24267@dhcp22.suse.cz> References: <20180725181115.hmlyd3tmnu3mn3sf@p50.austin.ibm.com> <20180725200336.GP28386@dhcp22.suse.cz> <20180727173259.htdxpn4i2fxprpaj@p50.austin.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180727173259.htdxpn4i2fxprpaj@p50.austin.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 27-07-18 12:32:59, John Allen wrote: > On Wed, Jul 25, 2018 at 10:03:36PM +0200, Michal Hocko wrote: > > On Wed 25-07-18 13:11:15, John Allen wrote: > > [...] > > > Does a failure in do_migrate_range indicate that the range is unmigratable > > > and the loop in __offline_pages should terminate and goto failed_removal? Or > > > should we allow a certain number of retrys before we > > > give up on migrating the range? > > > > Unfortunatelly not. Migration code doesn't tell a difference between > > ephemeral and permanent failures. We are relying on > > start_isolate_page_range to tell us this. So the question is, what kind > > of page is not migratable and for what reason. > > > > Are you able to add some debugging to give us more information. The > > current debugging code in the hotplug/migration sucks... > > After reproducing the problem a couple times, it seems that it can occur for > different types of pages. Running page-types on the offending page over two > separate instances produced the following: > > # tools/vm/page-types -a 307968-308224 > flags page-count MB symbolic-flags long-symbolic-flags > 0x0000000000000400 1 0 __________B________________________________ buddy > total 1 0 Huh! How come a buddy page has non zero reference count. > > And the following on a separate run: > > # tools/vm/page-types -a 313088-313344 > flags page-count MB symbolic-flags long-symbolic-flags > 0x000000000000006c 1 0 __RU_lA____________________________________ referenced,uptodate,lru,active > total 1 0 Hmm, what is the expected page count in this case? Seeing 1 doesn't look particularly wrong. -- Michal Hocko SUSE Labs