From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 23 Jul 2008 11:48:00 +0900 From: Yasunori Goto Subject: Re: memory hotplug: hot-remove fails on lowest chunk in ZONE_MOVABLE In-Reply-To: <1216745719.4871.8.camel@localhost.localdomain> References: <1216745719.4871.8.camel@localhost.localdomain> Message-Id: <20080723105318.81BC.E1E9C6FF@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Gerald Schaefer Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, KAMEZAWA Hiroyuki , Dave Hansen , Andy Whitcroft List-ID: Hi. > I've been testing memory hotplug on s390, on a system that starts w/o > memory in ZONE_MOVABLE at first, and then some memory chunks will be > added to ZONE_MOVABLE via memory hot-add. Now I observe the following > problem: > > Memory hot-remove of the lowest memory chunk in ZONE_MOVABLE will fail > because of some reserved pages at the beginning of each zone > (MIGRATE_RESERVED). > > During memory hot-add, setup_per_zone_pages_min() will be called from > online_pages() to redistribute/recalculate the reserved page blocks. > This will mark some page blocks at the beginning of each zone as > MIGRATE_RESERVE. Now, the memory chunk containing these blocks cannot > be set offline again, because only MIGRATE_MOVABLE pages can be isolated > (offline_pages -> start_isolate_page_range). > > So you cannot remove all the memory chunks that have been added via > memory hotplug. I'm not sure if I am missing something here, or if this > really is a bug. Any thoughts? I believe you are right. Current hot-remove code is NOT perfect. You may remove some sections, but may not other sections, because there are some un-removable pages by some reasons (not only MIGRATE_RESERVED). I think MIGRATE_RESERVED pages should be move to MIGRATE_MOVABLE when those pages must be removed, and should recalculate MIGRATE_RESERVED pages. Bye. -- Yasunori Goto -- 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