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From:   Wang Long <wanglong19@meituan.com>
To:     willy@infradead.org, akpm@linux-foundation.org,
        wanglong19@meituan.com, zwisler@kernel.org
Cc:     linux-kernel@vger.kernel.org, jack@suse.cz, heguanjun@meituan.com
Subject: [PATCH] radix-tree: optimization for radix_tree_init_maxnodes
Date:   Sun,  9 Sep 2018 21:21:00 +0800
Message-Id: <1536499260-126634-1-git-send-email-wanglong19@meituan.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

if i == 0, height_to_maxnodes[i] = 0,
if i >= 1, height_to_maxnodes[i] = height_to_maxnodes[i-1]
				+ __maxindex(i-1) + 1.

so delete height_to_maxindex and optimize the calculation of
height_to_maxnodes array.

Signed-off-by: Wang Long <wanglong19@meituan.com>
---
 lib/radix-tree.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index bc03ecc..af02b2c 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -2242,14 +2242,11 @@ static __init unsigned long __maxindex(unsigned int height)
 
 static __init void radix_tree_init_maxnodes(void)
 {
-	unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH + 1];
-	unsigned int i, j;
-
-	for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
-		height_to_maxindex[i] = __maxindex(i);
-	for (i = 0; i < ARRAY_SIZE(height_to_maxnodes); i++) {
-		for (j = i; j > 0; j--)
-			height_to_maxnodes[i] += height_to_maxindex[j - 1] + 1;
+	unsigned int i;
+
+	for (i = 1; i < ARRAY_SIZE(height_to_maxnodes); i++) {
+		height_to_maxnodes[i] = height_to_maxnodes[i - 1]
+					+  __maxindex(i - 1) + 1;
 	}
 }
 
-- 
1.8.3.1