[RFC PATCH] mm: memblock: optimize memblock_find_in_range_node() to minimize the search work

[Lin Feng <linfeng@cn.fujitsu.com>]

The memblock array is in ascending order and we traverse the memblock array in
reverse order so we can add some simple check to reduce the search work.

Tejun fix a underflow bug in 5d53cb27d8, but I think we could break there for
the same reason.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Lin Feng <linfeng@cn.fujitsu.com>
---
 mm/memblock.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 6259055..a710557 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -111,11 +111,18 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start,
 	end = max(start, end);
 
 	for_each_free_mem_range_reverse(i, nid, &this_start, &this_end, NULL) {
+		/*
+		 * exclude the regions out of the candidate range, since it's
+		 * likely to find a suitable range, we ignore the worst case.
+		 */
+		if (this_start >= end)
+			continue;
+
 		this_start = clamp(this_start, start, end);
 		this_end = clamp(this_end, start, end);
 
 		if (this_end < size)
-			continue;
+			break;
 
 		cand = round_down(this_end - size, align);
 		if (cand >= this_start)
-- 
1.7.11.7

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