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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, 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 4DF24C43441 for ; Thu, 15 Nov 2018 03:18:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1BE99214F1 for ; Thu, 15 Nov 2018 03:18:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1BE99214F1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1728139AbeKONYI (ORCPT ); Thu, 15 Nov 2018 08:24:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37852 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726807AbeKONYI (ORCPT ); Thu, 15 Nov 2018 08:24:08 -0500 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 mx1.redhat.com (Postfix) with ESMTPS id C324A89AD9; Thu, 15 Nov 2018 03:18:05 +0000 (UTC) Received: from localhost (ovpn-8-20.pek2.redhat.com [10.72.8.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E1A2A60BF6; Thu, 15 Nov 2018 03:18:04 +0000 (UTC) Date: Thu, 15 Nov 2018 11:18:01 +0800 From: Baoquan He To: Michal Hocko Cc: Andrew Morton , Oscar Salvador , linux-mm@kvack.org, LKML , Michal Hocko Subject: Re: [PATCH] mm, memory_hotplug: check zone_movable in has_unmovable_pages Message-ID: <20181115031801.GJ2653@MiWiFi-R3L-srv> References: <20181106095524.14629-1-mhocko@kernel.org> <20181115031325.GI2653@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181115031325.GI2653@MiWiFi-R3L-srv> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 15 Nov 2018 03:18:06 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/15/18 at 11:13am, Baoquan He wrote: > On 11/06/18 at 10:55am, Michal Hocko wrote: > > From: Michal Hocko > > > > Page state checks are racy. Under a heavy memory workload (e.g. stress > > -m 200 -t 2h) it is quite easy to hit a race window when the page is > > allocated but its state is not fully populated yet. A debugging patch to > > The original phenomenon is the value of /sys/devices/system/memory/memoryxxx/removable > is 0 on several memory blocks of hotpluggable node. And almost on each > hotpluggable node, there are one or several blocks which has this zero > value of removable attribute. It caused the hot removing failure always. > > And only cat /sys/devices/system/memory/memoryxxx/removable will trigger > the call trace. > > With this fix, all 'removable' of memory block on those hotpluggable > nodes are '1', and hotplug can succeed. Oh, by the way, hot removing/adding can always succeed when no memory pressure is added. The hot removing failure with high memory pressure has been raised in another thread. Thanks Baoquan > > > dump the struct page state shows > > : [ 476.575516] has_unmovable_pages: pfn:0x10dfec00, found:0x1, count:0x0 > > : [ 476.582103] page:ffffea0437fb0000 count:1 mapcount:1 mapping:ffff880e05239841 index:0x7f26e5000 compound_mapcount: 1 > > : [ 476.592645] flags: 0x5fffffc0090034(uptodate|lru|active|head|swapbacked) > > > > Note that the state has been checked for both PageLRU and PageSwapBacked > > already. Closing this race completely would require some sort of retry > > logic. This can be tricky and error prone (think of potential endless > > or long taking loops). > > > > Workaround this problem for movable zones at least. Such a zone should > > only contain movable pages. 15c30bc09085 ("mm, memory_hotplug: make > > has_unmovable_pages more robust") has told us that this is not strictly > > true though. Bootmem pages should be marked reserved though so we can > > move the original check after the PageReserved check. Pages from other > > zones are still prone to races but we even do not pretend that memory > > hotremove works for those so pre-mature failure doesn't hurt that much. > > > > Reported-and-tested-by: Baoquan He > > Acked-by: Baoquan He > > Fixes: "mm, memory_hotplug: make has_unmovable_pages more robust") > > Fixes: 15c30bc09085 "mm, memory_hotplug: make has_unmovable_pages more robust") > > > Signed-off-by: Michal Hocko > > --- > > > > Hi, > > this has been reported [1] and we have tried multiple things to address > > the issue. The only reliable way was to reintroduce the movable zone > > check into has_unmovable_pages. This time it should be safe also for > > the bug originally fixed by 15c30bc09085. > > > > [1] http://lkml.kernel.org/r/20181101091055.GA15166@MiWiFi-R3L-srv > > mm/page_alloc.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 863d46da6586..c6d900ee4982 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -7788,6 +7788,14 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, > > if (PageReserved(page)) > > goto unmovable; > > > > + /* > > + * If the zone is movable and we have ruled out all reserved > > + * pages then it should be reasonably safe to assume the rest > > + * is movable. > > + */ > > + if (zone_idx(zone) == ZONE_MOVABLE) > > + continue; > > + > > /* > > * Hugepages are not in LRU lists, but they're movable. > > * We need not scan over tail pages bacause we don't > > -- > > 2.19.1 > >