From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e36.co.us.ibm.com (8.13.1/8.13.1) with ESMTP id mB3MFUSl019988 for ; Wed, 3 Dec 2008 15:15:30 -0700 Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id mB3MGCuV191442 for ; Wed, 3 Dec 2008 15:16:12 -0700 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id mB3MGBD0009256 for ; Wed, 3 Dec 2008 15:16:12 -0700 Subject: Re: [PATCH] memory hotplug: run lru_add_drain_all() on each cpu From: Dave Hansen 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 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: 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 List-ID: 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org