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From:   Yejune Deng <yejune.deng@gmail.com>
To:     cl@linux.com, penberg@kernel.org, rientjes@google.com,
        iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        yejune.deng@gmail.com
Subject: [PATCH] include/linux/slab.h: use for() and left shift to calculate
Date:   Tue,  2 Mar 2021 11:39:08 +0800
Message-Id: <20210302033908.51706-1-yejune.deng@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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use for() and left shift to calculate the value that compared with size.

Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
---
 include/linux/slab.h | 32 ++++++++------------------------
 1 file changed, 8 insertions(+), 24 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 7ae604076767..0411f57930fb 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -347,6 +347,8 @@ static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags)
  */
 static __always_inline unsigned int kmalloc_index(size_t size)
 {
+	int i;
+
 	if (!size)
 		return 0;
 
@@ -357,30 +359,12 @@ static __always_inline unsigned int kmalloc_index(size_t size)
 		return 1;
 	if (KMALLOC_MIN_SIZE <= 64 && size > 128 && size <= 192)
 		return 2;
-	if (size <=          8) return 3;
-	if (size <=         16) return 4;
-	if (size <=         32) return 5;
-	if (size <=         64) return 6;
-	if (size <=        128) return 7;
-	if (size <=        256) return 8;
-	if (size <=        512) return 9;
-	if (size <=       1024) return 10;
-	if (size <=   2 * 1024) return 11;
-	if (size <=   4 * 1024) return 12;
-	if (size <=   8 * 1024) return 13;
-	if (size <=  16 * 1024) return 14;
-	if (size <=  32 * 1024) return 15;
-	if (size <=  64 * 1024) return 16;
-	if (size <= 128 * 1024) return 17;
-	if (size <= 256 * 1024) return 18;
-	if (size <= 512 * 1024) return 19;
-	if (size <= 1024 * 1024) return 20;
-	if (size <=  2 * 1024 * 1024) return 21;
-	if (size <=  4 * 1024 * 1024) return 22;
-	if (size <=  8 * 1024 * 1024) return 23;
-	if (size <=  16 * 1024 * 1024) return 24;
-	if (size <=  32 * 1024 * 1024) return 25;
-	if (size <=  64 * 1024 * 1024) return 26;
+
+	/* The maximum of size is 2^26 = 64 * 1024 * 1024 */
+	for (i = 3; i <= 26; i++) {
+		if (size <= (1 << i))
+			return i;
+	}
 	BUG();
 
 	/* Will never be reached. Needed because the compiler may complain */
-- 
2.29.0