percpu: allow non-linear / sparse cpu -> unit mapping

Currently cpu and unit are always identity mapped.  To allow more
efficient large page support on NUMA and lazy allocation for possible
but offline cpus, cpu -> unit mapping needs to be non-linear and/or
sparse.  This can be easily implemented by adding a cpu -> unit
mapping array and using it whenever looking up the matching unit for a
cpu.

The only unusal conversion is in pcpu_chunk_addr_search().  The passed
in address is unit0 based and unit0 might not be in use so it needs to
be converted to address of an in-use unit.  This is easily done by
adding the unit offset for the current processor.

[ Impact: allows non-linear/sparse cpu -> unit mapping, no visible change yet ]
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David Miller <davem@davemloft.net>

arch/sparc/kernel/smp_64.c

@@ -1516,7 +1516,7 @@ void __init setup_per_cpu_areas(void)
 
 	pcpu_unit_size = pcpu_setup_first_chunk(static_size,
 						PERCPU_MODULE_RESERVE, dyn_size,
-						PCPU_CHUNK_SIZE, vm.addr);
+						PCPU_CHUNK_SIZE, vm.addr, NULL);
 
 	free_bootmem(__pa(ptrs), ptrs_size);
 

include/linux/percpu.h

@@ -57,6 +57,7 @@
 #endif
 
 extern void *pcpu_base_addr;
+extern const int *pcpu_unit_map;
 
 typedef void * (*pcpu_fc_alloc_fn_t)(unsigned int cpu, size_t size);
 typedef void (*pcpu_fc_free_fn_t)(void *ptr, size_t size);
@@ -66,7 +67,7 @@ typedef void (*pcpu_fc_map_fn_t)(void *ptr, size_t size, void *addr);
 extern size_t __init pcpu_setup_first_chunk(
 				size_t static_size, size_t reserved_size,
 				ssize_t dyn_size, size_t unit_size,
-				void *base_addr);
+				void *base_addr, const int *unit_map);
 
 extern ssize_t __init pcpu_embed_first_chunk(
 				size_t static_size, size_t reserved_size,