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Commit 692223d1 authored by Fan Li's avatar Fan Li Committed by Jaegeuk Kim
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f2fs: optimize __find_rev_next_bit 



1. Skip __reverse_ulong if the bitmap is empty.
2. Reduce branches and codes.
According to my test, the performance of this new version is 5% higher on
an empty bitmap of 64bytes, and remains about the same in the worst scenario.

Signed-off-by: default avatarFan li <fanofcode.li@samsung.com>
Signed-off-by: default avatarJaegeuk Kim <jaegeuk@kernel.org>
parent eb7e813c

fs/f2fs/segment.c

+18 −28
Original line number Diff line number Diff line
@@ -86,6 +86,7 @@ static inline unsigned long __reverse_ffs(unsigned long word) 
/*

 * __find_rev_next(_zero)_bit is copied from lib/find_next_bit.c because

 * f2fs_set_bit makes MSB and LSB reversed in a byte.

 * @size must be integral times of unsigned long.

 * Example:

 *                             MSB <--> LSB

 *   f2fs_set_bit(0, bitmap) => 1000 0000
@@ -95,47 +96,36 @@ static unsigned long __find_rev_next_bit(const unsigned long *addr, 
			unsigned long size, unsigned long offset)

{

	const unsigned long *p = addr + BIT_WORD(offset);

	unsigned long result = offset & ~(BITS_PER_LONG - 1);

	unsigned long result = size;

	unsigned long tmp;



	if (offset >= size)

		return size;



	size -= result;

	size -= (offset & ~(BITS_PER_LONG - 1));

	offset %= BITS_PER_LONG;

	if (!offset)

		goto aligned;



	while (1) {

		if (*p == 0)

			goto pass;



		tmp = __reverse_ulong((unsigned char *)p);

	tmp &= ~0UL >> offset;



		tmp &= ~0UL >> offset;

		if (size < BITS_PER_LONG)

		goto found_first;

	if (tmp)

		goto found_middle;



	size -= BITS_PER_LONG;

	result += BITS_PER_LONG;

	p++;

aligned:

	while (size & ~(BITS_PER_LONG-1)) {

		tmp = __reverse_ulong((unsigned char *)p);

			tmp &= (~0UL << (BITS_PER_LONG - size));

		if (tmp)

			goto found_middle;

		result += BITS_PER_LONG;

			goto found;

pass:

		if (size <= BITS_PER_LONG)

			break;

		size -= BITS_PER_LONG;

		offset = 0;

		p++;

	}

	if (!size)

	return result;



	tmp = __reverse_ulong((unsigned char *)p);

found_first:

	tmp &= (~0UL << (BITS_PER_LONG - size));

	if (!tmp)		/* Are any bits set? */

		return result + size;   /* Nope. */

found_middle:

	return result + __reverse_ffs(tmp);

found:

	return result - size + __reverse_ffs(tmp);

}



static unsigned long __find_rev_next_zero_bit(const unsigned long *addr,