[PATCH] vmalloc: walk vmap_areas by sorted list instead of rb_next()

There's a walk by repeating rb_next to find a suitable hole. Could be
simply replaced by walk on the sorted vmap_area_list. More simpler and
efficient.

Mutation of the list and tree only happens in pair within
__insert_vmap_area and __free_vmap_area, under protection of
vmap_area_lock.  The patch code is also under vmap_area_lock, so the
list walk is safe, and consistent with the tree walk.

Tested on SMP by repeating batch of vmalloc anf vfree for random sizes
and rounds for hours.

Signed-off-by: Hong Zhiguo <redacted>
---
 mm/vmalloc.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 2aad499..0eb5347 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c

@@ -413,11 +413,11 @@ nocache:
 		if (addr + size - 1 < addr)
 			goto overflow;

-		n = rb_next(&first->rb_node);
-		if (n)
-			first = rb_entry(n, struct vmap_area, rb_node);
-		else
+		if (list_is_last(&first->list, &vmap_area_list))
 			goto found;
+
+		first = list_entry(first->list.next,
+				struct vmap_area, list);
 	}

 found:

-- 
1.7.4.1

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