Re: [PATCH] f2fs: introduce f2fs_find_next(_zero)_bit

[Changman Lee <cm224.lee@samsung.com>]

I agree. Your suggestion is more good.
Thanks for your review.

On 2013년 11월 15일 13:31, Jaegeuk Kim wrote:

> Hi,
>
> IMO, it would be better give names like __find_rev_next(_zero)_bit.
> If there is no objection, I'll modify and apply them by myself.
> Thanks, :)
>
> 2013-11-15 (금), 10:42 +0900, Changman Lee:
>> When f2fs_set_bit is used, in a byte MSB and LSB is reversed,
>> in that case we can use f2fs_find_next_bit or f2fs_find_next_zero_bit.
>>
>> Signed-off-by: Changman Lee <cm224.lee@samsung.com>
>> ---
>>   fs/f2fs/segment.c |  143 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 143 insertions(+)
>>
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index fa284d3..b2de887 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -21,6 +21,149 @@
>>   #include <trace/events/f2fs.h>
>>   
>>   /*
>> + * f2fs_ffs is copied from include/asm-generic/bitops/__ffs.h because
>> + * MSB and LSB is reversed in a byte by f2fs_set_bit.
>> + */
>> +static inline unsigned long f2fs_ffs(unsigned long word)
>> +{
>> +	int num = 0;
>> +
>> +#if BITS_PER_LONG == 64
>> +	if ((word & 0xffffffff) == 0) {
>> +		num += 32;
>> +		word >>= 32;
>> +	}
>> +#endif
>> +	if ((word & 0xffff) == 0) {
>> +		num += 16;
>> +		word >>= 16;
>> +	}
>> +	if ((word & 0xff) == 0) {
>> +		num += 8;
>> +		word >>= 8;
>> +	}
>> +	if ((word & 0xf0) == 0)
>> +		num += 4;
>> +	else
>> +		word >>= 4;
>> +	if ((word & 0xc) == 0)
>> +		num += 2;
>> +	else
>> +		word >>= 2;
>> +	if ((word & 0x2) == 0)
>> +		num += 1;
>> +	return num;
>> +}
>> +
>> +#define f2fs_ffz(x) f2fs_ffs(~(x))
>> +
>> +/*
>> + * f2fs_find_next(_zero)_bit is copied from lib/find_next_bit.c becasue
>> + * f2fs_set_bit makes MSB and LSB reversed in a byte.
>> + * Example:
>> + *                             LSB <--> MSB
>> + *   f2fs_set_bit(0, bitmap) => 0000 0001
>> + *   f2fs_set_bit(7, bitmap) => 1000 0000
>> + */
>> +static unsigned long f2fs_find_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 tmp;
>> +	unsigned long mask, submask;
>> +	unsigned long quot, rest;
>> +
>> +	if (offset >= size)
>> +		return size;
>> +	size -= result;
>> +	offset %= BITS_PER_LONG;
>> +	if (!offset)
>> +		goto aligned;
>> +	tmp = *(p++);
>> +	quot = (offset >> 3) << 3;
>> +	rest = offset & 0x7;
>> +	mask = ~0UL << quot;
>> +	submask = (unsigned char)(0xff << rest) >> rest;
>> +	submask <<= quot;
>> +	mask &= submask;
>> +	tmp &= mask;
>> +	if (size < BITS_PER_LONG)
>> +		goto found_first;
>> +	if (tmp)
>> +		goto found_middle;
>> +	size -= BITS_PER_LONG;
>> +	result += BITS_PER_LONG;
>> +aligned:
>> +	while (size & ~(BITS_PER_LONG-1)) {
>> +		tmp = *(p++);
>> +		if (tmp)
>> +			goto found_middle;
>> +		result += BITS_PER_LONG;
>> +		size -= BITS_PER_LONG;
>> +	}
>> +	if (!size)
>> +		return result;
>> +	tmp = *p;
>> +
>> +found_first:
>> +	tmp &= (~0UL >> (BITS_PER_LONG - size));
>> +	if (tmp == 0UL)		/* Are any bits set? */
>> +		return result + size;   /* Nope. */
>> +found_middle:
>> +	return result + f2fs_ffs(tmp);
>> +}
>> +
>> +static unsigned long f2fs_find_next_zero_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 tmp;
>> +	unsigned long mask, submask;
>> +	unsigned long quot, rest;
>> +
>> +	if (offset >= size)
>> +		return size;
>> +	size -= result;
>> +	offset %= BITS_PER_LONG;
>> +	if (!offset)
>> +		goto aligned;
>> +	tmp = *(p++);
>> +	quot = (offset >> 3) << 3;
>> +	rest = offset & 0x7;
>> +	mask = ~(~0UL << quot);
>> +	submask = (unsigned char)~((unsigned char)(0xff << rest) >> rest);
>> +	submask <<= quot;
>> +	mask += submask;
>> +	tmp |= mask;
>> +	if (size < BITS_PER_LONG)
>> +		goto found_first;
>> +	if (~tmp)
>> +		goto found_middle;
>> +	size -= BITS_PER_LONG;
>> +	result += BITS_PER_LONG;
>> +aligned:
>> +	while (size & ~(BITS_PER_LONG - 1)) {
>> +		tmp = *(p++);
>> +		if (~tmp)
>> +			goto found_middle;
>> +		result += BITS_PER_LONG;
>> +		size -= BITS_PER_LONG;
>> +	}
>> +	if (!size)
>> +		return result;
>> +	tmp = *p;
>> +
>> +found_first:
>> +	tmp |= ~0UL << size;
>> +	if (tmp == ~0UL)        /* Are any bits zero? */
>> +		return result + size;   /* Nope. */
>> +found_middle:
>> +	return result + f2fs_ffz(tmp);
>> +}
>> +
>> +/*
>>    * This function balances dirty node and dentry pages.
>>    * In addition, it controls garbage collection.
>>    */


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