Messages in this thread | | | 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 |
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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
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