From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755488AbYLCWQ3 (ORCPT ); Wed, 3 Dec 2008 17:16:29 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752730AbYLCWQV (ORCPT ); Wed, 3 Dec 2008 17:16:21 -0500 Received: from e38.co.us.ibm.com ([32.97.110.159]:49662 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751884AbYLCWQU (ORCPT ); Wed, 3 Dec 2008 17:16:20 -0500 Subject: Re: [PATCH] memory hotplug: run lru_add_drain_all() on each cpu From: Dave Hansen To: gerald.schaefer@de.ibm.com Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, kamezawa.hiroyu@jp.fujitsu.com, y-goto@jp.fujitsu.com, npiggin@suse.de In-Reply-To: <1228339524.6598.11.camel@t60p> References: <1228339524.6598.11.camel@t60p> Content-Type: text/plain Date: Wed, 03 Dec 2008 14:16:07 -0800 Message-Id: <1228342567.13111.11.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2008-12-03 at 22:25 +0100, Gerald Schaefer wrote: > offline_pages() calls lru_add_drain_all() followed by drain_all_pages(). > While drain_all_pages() works on each cpu, lru_add_drain_all() only runs > on the current cpu for architectures w/o CONFIG_NUMA. I'm a bit confused why this is. Is this because the LRUs are per-zone and we expected !CONFIG_NUMA systems to only have LRUs sitting on the same (only) node as the current CPU? This doesn't make any sense, though. The pagevecs that drain_cpu_pagevecs() actually empties out are per-cpu. > This let us run > into the BUG_ON(!PageBuddy(page)) in __offline_isolated_pages() during > memory hotplug stress test on s390. The page in question was still on the > pcp list, because of a race with lru_add_drain_all() and drain_all_pages() > on different cpus. > > This is fixed with this patch by adding CONFIG_MEMORY_HOTREMOVE to the > lru_add_drain_all() #ifdef, to let it run on each cpu. This doesn't seem right to me. CONFIG_MEMORY_HOTREMOVE doesn't change the layout of the LRUs, unlike NUMA or UNEVICTABLE_LRU. So, I think this bug is more due to the hotremove code mis-expecting behavior out of lru_add_drain_all(). Why does this not affect the other lru_add_drain_all() users? -- Dave