From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d06nrmr1407.portsmouth.uk.ibm.com (d06nrmr1407.portsmouth.uk.ibm.com [9.149.38.185]) by mtagate2.uk.ibm.com (8.13.1/8.13.1) with ESMTP id mB5D8XRS016144 for ; Fri, 5 Dec 2008 13:08:33 GMT Received: from d06av01.portsmouth.uk.ibm.com (d06av01.portsmouth.uk.ibm.com [9.149.37.212]) by d06nrmr1407.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id mB5D8XMY2179298 for ; Fri, 5 Dec 2008 13:08:33 GMT Received: from d06av01.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av01.portsmouth.uk.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id mB5D8WXM000572 for ; Fri, 5 Dec 2008 13:08:33 GMT Subject: Re: [PATCH] memory hotplug: run lru_add_drain_all() on each cpu From: Gerald Schaefer Reply-To: gerald.schaefer@de.ibm.com In-Reply-To: <1228342567.13111.11.camel@nimitz> References: <1228339524.6598.11.camel@t60p> <1228342567.13111.11.camel@nimitz> Content-Type: text/plain Date: Fri, 05 Dec 2008 14:08:20 +0100 Message-Id: <1228482500.8392.15.camel@t60p> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Dave Hansen 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 14:16 -0800, Dave Hansen wrote: > 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. Right, the pagevecs are per-cpu, independent from any CONFIG_NUMA settings, and this is exactly why I would expect that lru_add_drain_all() works on all cpus, as opposed to lru_add_drain() which works only on the current 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? Good question, there are only a few other users and most of them were added just recently with the unevictable lru patches. The only exception is migrate_prep(), but this is only called from sys_move_pages(), which is not implemented w/o CONFIG_NUMA afaik. As explained above, the per-cpu pagevec layout should be independent from NUMA or UNEVICTABLE_LRU, so I guess the right thing to do here is completely remove the #ifdef as in the patch from Kosaki Motohiro (or at least replace it with a CONFIG_SMP as suggested by Kamezawa Hiroyuki). Thanks, Gerald -- 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