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Commit 0fed3ac8 authored by George Spelvin's avatar George Spelvin Committed by Linus Torvalds
Browse files

namei: Improve hash mixing if CONFIG_DCACHE_WORD_ACCESS 



The hash mixing between adding the next 64 bits of name
was just a bit weak.

Replaced with a still very fast but slightly more effective
mixing function.

Signed-off-by: default avatarGeorge Spelvin <linux@horizon.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2dcd0af5

fs/namei.c

+26 −7
Original line number Diff line number Diff line
@@ -1794,30 +1794,49 @@ static inline unsigned int fold_hash(unsigned long hash) 
	return hash_64(hash, 32);

}



/*

 * This is George Marsaglia's XORSHIFT generator.

 * It implements a maximum-period LFSR in only a few

 * instructions.  It also has the property (required

 * by hash_name()) that mix_hash(0) = 0.

 */

static inline unsigned long mix_hash(unsigned long hash)

{

	hash ^= hash << 13;

	hash ^= hash >> 7;

	hash ^= hash << 17;

	return hash;

}



#else	/* 32-bit case */



#define fold_hash(x) (x)



static inline unsigned long mix_hash(unsigned long hash)

{

	hash ^= hash << 13;

	hash ^= hash >> 17;

	hash ^= hash << 5;

	return hash;

}



#endif



unsigned int full_name_hash(const unsigned char *name, unsigned int len)

{

	unsigned long a, mask;

	unsigned long hash = 0;

	unsigned long a, hash = 0;



	for (;;) {

		a = load_unaligned_zeropad(name);

		if (len < sizeof(unsigned long))

			break;

		hash += a;

		hash *= 9;

		hash = mix_hash(hash + a);

		name += sizeof(unsigned long);

		len -= sizeof(unsigned long);

		if (!len)

			goto done;

	}

	mask = bytemask_from_count(len);

	hash += mask & a;

	hash += a & bytemask_from_count(len);

done:

	return fold_hash(hash);

}
@@ -1835,7 +1854,7 @@ static inline u64 hash_name(const char *name) 
	hash = a = 0;

	len = -sizeof(unsigned long);

	do {

		hash = (hash + a) * 9;

		hash = mix_hash(hash + a);

		len += sizeof(unsigned long);

		a = load_unaligned_zeropad(name+len);

		b = a ^ REPEAT_BYTE('/');