linux-kernel - Re: [PATCH v2] blkdev: Replace blksize

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Message-ID: <20200529202713.GC19604@bombadil.infradead.org>
Date:   Fri, 29 May 2020 13:27:13 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Kaitao Cheng <pilgrimtao@...il.com>
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Subject: Re: [PATCH v2] blkdev: Replace blksize_bits() with ilog2()

On Fri, May 29, 2020 at 10:11:00PM +0800, Kaitao Cheng wrote:
> There is a function named ilog2() exist which can replace blksize.
> The generated code will be shorter and more efficient on some
> architecture, such as arm64. And ilog2() can be optimized according
> to different architecture.

We'd get the same benefit from a smaller patch with just:

--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1502,15 +1502,9 @@ static inline int blk_rq_aligned(struct request_queue *q, unsigned long addr,
 	return !(addr & alignment) && !(len & alignment);
 }
 
-/* assumes size > 256 */
 static inline unsigned int blksize_bits(unsigned int size)
 {
-	unsigned int bits = 8;
-	do {
-		bits++;
-		size >>= 1;
-	} while (size > 256);
-	return bits;
+	return ilog2(size);
 }
 
 static inline unsigned int block_size(struct block_device *bdev)