We have had several reports  that page allocator blows up when an allocation from a possible node is requested. The underlying reason is that NODE_DATA for the specific node is not allocated.
NUMA specific initialization is arch specific and it can vary a lot. E.g. x86 tries to initialize all nodes that have some cpu affinity (see init_cpu_to_node) but this can be insufficient because the node might be cpuless for example.
One way to address this problem would be to check for !node_online nodes when trying to get a zonelist and silently fall back to another node. That is unfortunately adding a branch into allocator hot path and it doesn't handle any other potential NODE_DATA users.
This patch takes a different approach (following a lead of ) and it pre allocates pgdat for all possible nodes in an arch indipendent code -free_area_init. All uninitialized nodes are treated as memoryless nodes. node_state of the node is not changed because that would lead to other side effects - e.g. sysfs representation of such a node and from past discussions  it is known that some tools might have problems digesting that.
Newly allocated pgdat only gets a minimal initialization and the rest of the work is expected to be done by the memory hotplug - hotadd_new_pgdat (renamed to hotadd_init_pgdat).
generic_alloc_nodedata is changed to use the memblock allocator because neither page nor slab allocators are available at the stage when all pgdats are allocated. Hotplug doesn't allocate pgdat anymore so we can use the early boot allocator. The only arch specific implementation is ia64 and that is changed to use the early allocator as well.
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[firstname.lastname@example.org: replace comment, per Mike]
09f49dca570a mm: handle uninitialized numa nodes gracefully
arch/ia64/mm/discontig.c | 4 ++--
include/linux/memory_hotplug.h | 2 +-
mm/internal.h | 2 ++
mm/memory_hotplug.c | 21 +++++++++------------
mm/page_alloc.c | 40 ++++++++++++++++++++++++++++++++++++----
5 files changed, 50 insertions(+), 19 deletions(-)