Hi Andrew, Could you consider this patch for inclusion into mainline kernel? It alleviates some issues seen with Linux when accessing millions of files on machines with large amounts of RAM (+32GB). Both algorithms are base on some studies that Dominique Heger was doing on hash table efficiencies in Linux. The dentry hash table has been tested in small systems with one internal IDE hard disk as well as in large SMP with many fiberchanel disks. Dominique claims that in all the testing done, they did not see one case were this has function provided worst performance and that in most test they were seeing better performance. The inode hash function was done by me base on Dominique's original work and has only been stress tested with SpecSFS. It provided a 3% improvement over the default algorithm in the SpecSFS results and speed ups in the response time of almost all filesystem operations the benchmark stress. With the better distribution is as also possible to reduce the number of inode buckets for 32 million to 16 million and still get a slightly better results. Anton was nice enough to provide some graphs that show the distribution before and after the patch at http://samba.org/~anton/linux/sfs/1/ Thanks -JRS # This is a BitKeeper generated patch for the following project: # Project Name: Linux kernel tree # This patch format is intended for GNU patch command version 2.5 or higher. # This patch includes the following deltas: # ChangeSet 1.1582 -> 1.1583 # fs/dcache.c 1.70 -> 1.71 # fs/inode.c 1.113 -> 1.114 # # The following is the BitKeeper ChangeSet Log # -------------------------------------------- # 04/04/30 jsantos@rx8.austin.ibm.com 1.1583 # Hash functions changes that show improvements on SpecSFS when a large amount of files is used (+20 Million). # -------------------------------------------- # diff -Nru a/fs/dcache.c b/fs/dcache.c --- a/fs/dcache.c Fri Apr 30 12:14:23 2004 +++ b/fs/dcache.c Fri Apr 30 12:14:23 2004 @@ -28,6 +28,7 @@ #include <asm/uaccess.h> #include <linux/security.h> #include <linux/seqlock.h> +#include <linux/hash.h> #define DCACHE_PARANOIA 1 /* #define DCACHE_DEBUG 1 */ @@ -799,8 +800,8 @@ static inline struct hlist_head * d_hash(struct dentry * parent, unsigned long hash) { - hash += (unsigned long) parent / L1_CACHE_BYTES; - hash = hash ^ (hash >> D_HASHBITS); + hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES; + hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS); return dentry_hashtable + (hash & D_HASHMASK); } diff -Nru a/fs/inode.c b/fs/inode.c --- a/fs/inode.c Fri Apr 30 12:14:23 2004 +++ b/fs/inode.c Fri Apr 30 12:14:23 2004 @@ -671,8 +671,9 @@ static inline unsigned long hash(struct super_block *sb, unsigned long hashval) { - unsigned long tmp = hashval + ((unsigned long) sb / L1_CACHE_BYTES); - tmp = tmp + (tmp >> I_HASHBITS); + unsigned long tmp = (hashval + ((unsigned long) sb) ^ (GOLDEN_RATIO_PRIME + hashval) + / L1_CACHE_BYTES); + tmp = tmp + ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS); return tmp & I_HASHMASK; } - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
