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

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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: George Spelvin <linux@sciencehorizons.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
George Spelvin
2016-06-10 00:22:12 -04:00
committed by Linus Torvalds
parent 8387ff2577
commit 703b5faf22
2 changed files with 5 additions and 3 deletions
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2
fs/dcache.c
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@@ -106,7 +106,7 @@ static struct hlist_bl_head *dentry_hashtable __read_mostly;
static inline struct hlist_bl_head *d_hash(unsigned int hash) 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 #define IN_LOOKUP_SHIFT 10

6
include/linux/stringhash.h
View File

@@ -3,6 +3,7 @@
#include <linux/compiler.h> /* For __pure */ #include <linux/compiler.h> /* For __pure */
#include <linux/types.h> /* For u32, u64 */ #include <linux/types.h> /* For u32, u64 */
#include <linux/hash.h>
/* /*
* Routines for hashing strings of bytes to a 32-bit hash value. * 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 * 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) static inline unsigned long end_name_hash(unsigned long hash)
{ {
return (unsigned int)hash; return __hash_32((unsigned int)hash);
} }
/* /*