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Commit 703b5faf authored by George Spelvin's avatar George Spelvin Committed by Linus Torvalds
Browse files

fs/dcache.c: Save one 32-bit multiply in dcache lookup 



Noe that we're mixing in the parent pointer earlier, we
don't need to use hash_32() to mix its bits.  Instead, we can
just take the msbits of the hash value directly.

For those applications which use the partial_name_hash(),
move the multiply to end_name_hash.

Signed-off-by: default avatarGeorge Spelvin <linux@sciencehorizons.net>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8387ff25

fs/dcache.c

+1 −1
Original line number Diff line number Diff line
@@ -106,7 +106,7 @@ static struct hlist_bl_head *dentry_hashtable __read_mostly; 


static inline struct hlist_bl_head *d_hash(unsigned int hash)

{

	return dentry_hashtable + hash_32(hash, d_hash_shift);

	return dentry_hashtable + (hash >> (32 - d_hash_shift));

}



#define IN_LOOKUP_SHIFT 10

include/linux/stringhash.h

+4 −2
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 


#include <linux/compiler.h>	/* For __pure */

#include <linux/types.h>	/* For u32, u64 */

#include <linux/hash.h>



/*

 * Routines for hashing strings of bytes to a 32-bit hash value.
@@ -45,11 +46,12 @@ partial_name_hash(unsigned long c, unsigned long prevhash) 


/*

 * Finally: cut down the number of bits to a int value (and try to avoid

 * losing bits)

 * losing bits).  This also has the property (wanted by the dcache)

 * that the msbits make a good hash table index.

 */

static inline unsigned long end_name_hash(unsigned long hash)

{

	return (unsigned int)hash;

	return __hash_32((unsigned int)hash);

}



/*