[PATCH] percpu: add comment to per_cpu_ptr_to_phys
dyoung at redhat.com
Wed Nov 23 03:45:43 EST 2011
add comments about current per_cpu_ptr_to_phys implementation
to explain why the logic is more complicated than necessary.
Signed-off-by: Dave Young <dyoung at redhat.com>
mm/percpu.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
--- linux-2.6.orig/mm/percpu.c 2011-11-22 10:18:46.000000000 +0800
+++ linux-2.6/mm/percpu.c 2011-11-23 16:27:01.667562973 +0800
@@ -988,6 +988,19 @@ phys_addr_t per_cpu_ptr_to_phys(void *ad
unsigned int cpu;
+ * percpu allocator has special setup for the first chunk,
+ * which currently supports either embedding in linear address space
+ * or vmalloc mapping, and, from the second one, the backing
+ * allocator (currently either vm or km) provides translation.
+ * The addr can be tranlated simply without checking if it falls
+ * into the first chunk. But the current code reflects better
+ * how percpu allocator actually works, and the verification can
+ * discover both bugs in percpu allocator itself and
+ * per_cpu_ptr_to_phys() callers. So we keep current code.
* The following test on first_start/end isn't strictly
* necessary but will speed up lookups of addresses which
* aren't in the first chunk.
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