percpu: implement kernel memory based chunk allocation

Implement an alternate percpu chunk management based on kernel memeory
for nommu SMP architectures.  Instead of mapping into vmalloc area,
chunks are allocated as a contiguous kernel memory using
alloc_pages().  As such, percpu allocator on nommu will have the
following restrictions.

* It can't fill chunks on-demand page-by-page.  It has to allocate
  each chunk fully upfront.

* It can't support sparse chunk for NUMA configurations.  SMP w/o mmu
  is crazy enough.  Let's hope no one does NUMA w/o mmu.  :-P

* If chunk size isn't power-of-two multiple of PAGE_SIZE, the
  unaligned amount will be wasted on each chunk.  So, archs which use
  this better align chunk size.

For instructions on how to use this, read the comment on top of
mm/percpu-km.c.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: David Howells <dhowells@redhat.com>
Cc: Graff Yang <graff.yang@gmail.com>
Cc: Sonic Zhang <sonic.adi@gmail.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index 15f680430671..39f7dfd59585 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -654,7 +654,11 @@ static void pcpu_destroy_chunk(struct pcpu_chunk *chunk);
 static struct page *pcpu_addr_to_page(void *addr);
 static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);
 
+#ifdef CONFIG_NEED_PER_CPU_KM
+#include "percpu-km.c"
+#else
 #include "percpu-vm.c"
+#endif
 
 /**
  * pcpu_chunk_addr_search - determine chunk containing specified address