From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 103F86B004A for ; Thu, 18 Nov 2010 20:53:32 -0500 (EST) Date: Fri, 19 Nov 2010 08:32:25 +0800 From: Shaohui Zheng Subject: Re: [2/8,v3] NUMA Hotplug Emulator: infrastructure of NUMA hotplug emulation Message-ID: <20101119003225.GB3327@shaohui> References: <20101117020759.016741414@intel.com> <20101117021000.568681101@intel.com> <20101117075128.GA30254@shaohui> <20101118041407.GA2408@shaohui> <20101118062715.GD17539@linux-sh.org> <20101118052750.GD2408@shaohui> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: David Rientjes Cc: Paul Mundt , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, haicheng.li@linux.intel.com, ak@linux.intel.com, shaohui.zheng@linux.intel.com, Yinghai Lu , Haicheng Li List-ID: On Thu, Nov 18, 2010 at 01:24:52PM -0800, David Rientjes wrote: > On Thu, 18 Nov 2010, Shaohui Zheng wrote: > > > in our draft patch, we re-setup nr_node_ids when CONFIG_ARCH_MEMORY_PROBE enabled > > and mem=XXX was specified in grub. we set nr_node_ids as MAX_NUMNODES + 1, because > > we do not know how many nodes will be hot-added through memory/probe interface. > > it might be a little wasting of memory. > > > > nr_node_ids need not be set to anything different at boot, the > MEM_GOING_ONLINE callback should be used for anything (like the slab > allocators) where a new node is introduced and needs to be dealt with > accordingly; this is how regular memory hotplug works, we need no > additional code in this regard because it's emulated. If a subsystem > needs to change in response to a new node going online and doesn't as a > result of using your emulator, that's a bug and either needs to be fixed > or prohibited from use with CONFIG_MEMORY_HOTPLUG. > > (See the MEM_GOING_ONLINE callback in mm/slub.c, for instance, which deals > only with the case of node hotplug.) nr_node_ids is the possible node number. when we do regular memory online, it is oline to a possible node, and it is already counted in to nr_node_ids. if you increment nr_node_ids dynamically when node online, it causes a lot of problems. Many data are initialized according to nr_node_ids. That is our experience when we debug the emulator. mm/page_alloc.c: /* * Figure out the number of possible node ids. */ static void __init setup_nr_node_ids(void) { unsigned int node; unsigned int highest = 0; for_each_node_mask(node, node_possible_map) highest = node; nr_node_ids = highest + 1; } There is no conflict between emulator and CONFIG_MEMORY_HOTPLUG. A real node can be onlined because we already set it as _possible_; if emulator is enabled, all the nodes were marked as _possbile_ node, the real ndoe is also included in. -- Thanks & Regards, Shaohui -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org