From 8387ff2577eb9ed245df9a39947f66976c6bcd02 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 10 Jun 2016 07:51:30 -0700 Subject: vfs: make the string hashes salt the hash We always mixed in the parent pointer into the dentry name hash, but we did it late at lookup time. It turns out that we can simplify that lookup-time action by salting the hash with the parent pointer early instead of late. A few other users of our string hashes also wanted to mix in their own pointers into the hash, and those are updated to use the same mechanism. Hash users that don't have any particular initial salt can just use the NULL pointer as a no-salt. Cc: Vegard Nossum Cc: George Spelvin Cc: Al Viro Signed-off-by: Linus Torvalds --- include/linux/stringhash.h | 6 +++--- include/linux/sunrpc/svcauth.h | 4 ++-- 2 files changed, 5 insertions(+), 5 deletions(-) (limited to 'include') diff --git a/include/linux/stringhash.h b/include/linux/stringhash.h index 451771d9b9c0..eb7debb280c0 100644 --- a/include/linux/stringhash.h +++ b/include/linux/stringhash.h @@ -34,7 +34,7 @@ */ /* Hash courtesy of the R5 hash in reiserfs modulo sign bits */ -#define init_name_hash() 0 +#define init_name_hash(salt) (unsigned long)(salt) /* partial hash update function. Assume roughly 4 bits per character */ static inline unsigned long @@ -60,7 +60,7 @@ static inline unsigned long end_name_hash(unsigned long hash) * * If not set, this falls back to a wrapper around the preceding. */ -extern unsigned int __pure full_name_hash(const char *, unsigned int); +extern unsigned int __pure full_name_hash(const void *salt, const char *, unsigned int); /* * A hash_len is a u64 with the hash of a string in the low @@ -71,6 +71,6 @@ extern unsigned int __pure full_name_hash(const char *, unsigned int); #define hashlen_create(hash, len) ((u64)(len)<<32 | (u32)(hash)) /* Return the "hash_len" (hash and length) of a null-terminated string */ -extern u64 __pure hashlen_string(const char *name); +extern u64 __pure hashlen_string(const void *salt, const char *name); #endif /* __LINUX_STRINGHASH_H */ diff --git a/include/linux/sunrpc/svcauth.h b/include/linux/sunrpc/svcauth.h index 91d5a5d6f52b..d03932055328 100644 --- a/include/linux/sunrpc/svcauth.h +++ b/include/linux/sunrpc/svcauth.h @@ -172,12 +172,12 @@ extern void unix_gid_cache_destroy(struct net *net); */ static inline unsigned long hash_str(char const *name, int bits) { - return hashlen_hash(hashlen_string(name)) >> (32 - bits); + return hashlen_hash(hashlen_string(NULL, name)) >> (32 - bits); } static inline unsigned long hash_mem(char const *buf, int length, int bits) { - return full_name_hash(buf, length) >> (32 - bits); + return full_name_hash(NULL, buf, length) >> (32 - bits); } #endif /* __KERNEL__ */ -- cgit v1.2.3 From 703b5faf22fbddf984a361e6555f3a03fdba63d9 Mon Sep 17 00:00:00 2001 From: George Spelvin Date: Fri, 10 Jun 2016 00:22:12 -0400 Subject: 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: George Spelvin Signed-off-by: Linus Torvalds --- fs/dcache.c | 2 +- include/linux/stringhash.h | 6 ++++-- 2 files changed, 5 insertions(+), 3 deletions(-) (limited to 'include') diff --git a/fs/dcache.c b/fs/dcache.c index 9522b8b63871..03f1a332f677 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -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 diff --git a/include/linux/stringhash.h b/include/linux/stringhash.h index eb7debb280c0..7c2d95170d01 100644 --- a/include/linux/stringhash.h +++ b/include/linux/stringhash.h @@ -3,6 +3,7 @@ #include /* For __pure */ #include /* For u32, u64 */ +#include /* * 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); } /* -- cgit v1.2.3