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authorDave Young <dyoung@redhat.com>2011-11-23 08:20:53 -0800
committerTejun Heo <tj@kernel.org>2011-11-23 08:20:53 -0800
commit67589c71456b0346500629967292dea3802230b6 (patch)
tree2fdbe50888cc77b740862c0f6f182082a4aeeab9
parenta855b84c3d8c73220d4d3cd392a7bee7c83de70e (diff)
percpu: explain why per_cpu_ptr_to_phys() is more complicated than necessary
Add comments about current per_cpu_ptr_to_phys implementation to explain why the logic is more complicated than necessary. -tj: relocated comment into kerneldoc comment Signed-off-by: Dave Young <dyoung@redhat.com> Signed-off-by: Tejun Heo <tj@kernel.org>
-rw-r--r--mm/percpu.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/mm/percpu.c b/mm/percpu.c
index 2473ff06dc7..3bb810a7200 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -978,6 +978,17 @@ bool is_kernel_percpu_address(unsigned long addr)
* address. The caller is responsible for ensuring @addr stays valid
* until this function finishes.
*
+ * 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.
+ *
* RETURNS:
* The physical address for @addr.
*/