dm: improve hash_locks sizing and hash function

[linux-2.6-microblaze.git] / drivers / md / dm.h

diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index a1a5def..a856e0a 100644 (file)
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -233,9 +233,21 @@ unsigned int dm_get_reserved_bio_based_ios(void);
 
 static inline unsigned int dm_num_hash_locks(void)
 {
-       unsigned int num_locks = roundup_pow_of_two(num_online_cpus());
+       unsigned int num_locks = roundup_pow_of_two(num_online_cpus()) << 1;
 
        return min_t(unsigned int, num_locks, DM_HASH_LOCKS_MAX);
 }
 
+#define DM_HASH_LOCKS_MULT  4294967291ULL
+#define DM_HASH_LOCKS_SHIFT 6
+
+static inline unsigned int dm_hash_locks_index(sector_t block,
+                                              unsigned int num_locks)
+{
+       sector_t h1 = (block * DM_HASH_LOCKS_MULT) >> DM_HASH_LOCKS_SHIFT;
+       sector_t h2 = h1 >> DM_HASH_LOCKS_SHIFT;
+
+       return (h1 ^ h2) & (num_locks - 1);
+}
+
 #endif