Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753793Ab3EOXU5 (ORCPT ); Wed, 15 May 2013 19:20:57 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:34527 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753265Ab3EOXU4 (ORCPT ); Wed, 15 May 2013 19:20:56 -0400 Date: Wed, 15 May 2013 16:20:54 -0700 From: Andrew Morton To: Cody P Schafer Cc: David Rientjes , Linux MM , LKML Subject: Re: [PATCH v3 3/4] memory_hotplug: use pgdat_resize_lock() in online_pages() Message-Id: <20130515162054.1c76200ee9514ca8a2054628@linux-foundation.org> In-Reply-To: <1368486787-9511-4-git-send-email-cody@linux.vnet.ibm.com> References: <1368486787-9511-1-git-send-email-cody@linux.vnet.ibm.com> <1368486787-9511-4-git-send-email-cody@linux.vnet.ibm.com> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1826 Lines: 55 On Mon, 13 May 2013 16:13:06 -0700 Cody P Schafer wrote: > mmzone.h documents node_size_lock (which pgdat_resize_lock() locks) as > follows: > > * Must be held any time you expect node_start_pfn, node_present_pages > * or node_spanned_pages stay constant. [...] Yeah, I suppose so. Although no present code sites actually do that. > So actually hold it when we update node_present_pages in online_pages(). > > ... > > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -915,6 +915,7 @@ static void node_states_set_node(int node, struct memory_notify *arg) > > int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_type) > { > + unsigned long flags; > unsigned long onlined_pages = 0; > struct zone *zone; > int need_zonelists_rebuild = 0; > @@ -993,7 +994,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ > > zone->managed_pages += onlined_pages; > zone->present_pages += onlined_pages; > + > + pgdat_resize_lock(zone->zone_pgdat, &flags); > zone->zone_pgdat->node_present_pages += onlined_pages; > + pgdat_resize_unlock(zone->zone_pgdat, &flags); > + > if (onlined_pages) { > node_states_set_node(zone_to_nid(zone), &arg); > if (need_zonelists_rebuild) afaict the only benefits of making this change are a) so that code which does a = p->node_present_pages; ... b = p->node_present_pages; can ensure that `a' and `b' are equal, by taking pgdat_resize_lock(). Which is somewhat odd, and b) to make the comment truthful ;) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/