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fat: improve fat_hash()

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fat_hash() is using the algorithm known as bad. Instead of it, this
uses hash_32(). The following is the summary of test.

old hash:
	hash func (1000 times): 33489 cycles
	total inodes in hash table: 70926
	largest bucket contains: 696
	smallest bucket contains: 54

new hash:
	hash func (1000 times): 33129 cycles
	total inodes in hash table: 70926
	largest bucket contains: 315
	smallest bucket contains: 236

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
OGAWA Hirofumi 2008-11-06 12:53:49 -08:00 committed by Linus Torvalds
parent 52e9d9f4b3
commit d3dfa8228f
2 changed files with 7 additions and 12 deletions
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1
fs/fat/fat.h
View file

@ -43,7 +43,6 @@ struct fat_mount_options {
#define FAT_HASH_BITS 8 #define FAT_HASH_BITS 8
#define FAT_HASH_SIZE (1UL << FAT_HASH_BITS) #define FAT_HASH_SIZE (1UL << FAT_HASH_BITS)
#define FAT_HASH_MASK (FAT_HASH_SIZE-1)
/* /*
* MS-DOS file system in-core superblock data * MS-DOS file system in-core superblock data

18
fs/fat/inode.c
View file

@ -26,6 +26,7 @@
#include <linux/uio.h> #include <linux/uio.h>
#include <linux/writeback.h> #include <linux/writeback.h>
#include <linux/log2.h> #include <linux/log2.h>
#include <linux/hash.h>
#include <asm/unaligned.h> #include <asm/unaligned.h>
#include "fat.h" #include "fat.h"
@ -247,25 +248,21 @@ static void fat_hash_init(struct super_block *sb)
INIT_HLIST_HEAD(&sbi->inode_hashtable[i]); INIT_HLIST_HEAD(&sbi->inode_hashtable[i]);
} }
static inline unsigned long fat_hash(struct super_block *sb, loff_t i_pos) static inline unsigned long fat_hash(loff_t i_pos)
{ {
unsigned long tmp = (unsigned long)i_pos | (unsigned long) sb; return hash_32(i_pos, FAT_HASH_BITS);
tmp = tmp + (tmp >> FAT_HASH_BITS) + (tmp >> FAT_HASH_BITS * 2);
return tmp & FAT_HASH_MASK;
} }
void fat_attach(struct inode *inode, loff_t i_pos) void fat_attach(struct inode *inode, loff_t i_pos)
{ {
struct super_block *sb = inode->i_sb; struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
struct msdos_sb_info *sbi = MSDOS_SB(sb); struct hlist_head *head = sbi->inode_hashtable + fat_hash(i_pos);
spin_lock(&sbi->inode_hash_lock); spin_lock(&sbi->inode_hash_lock);
MSDOS_I(inode)->i_pos = i_pos; MSDOS_I(inode)->i_pos = i_pos;
hlist_add_head(&MSDOS_I(inode)->i_fat_hash, hlist_add_head(&MSDOS_I(inode)->i_fat_hash, head);
sbi->inode_hashtable + fat_hash(sb, i_pos));
spin_unlock(&sbi->inode_hash_lock); spin_unlock(&sbi->inode_hash_lock);
} }
EXPORT_SYMBOL_GPL(fat_attach); EXPORT_SYMBOL_GPL(fat_attach);
void fat_detach(struct inode *inode) void fat_detach(struct inode *inode)
@ -276,13 +273,12 @@ void fat_detach(struct inode *inode)
hlist_del_init(&MSDOS_I(inode)->i_fat_hash); hlist_del_init(&MSDOS_I(inode)->i_fat_hash);
spin_unlock(&sbi->inode_hash_lock); spin_unlock(&sbi->inode_hash_lock);
} }
EXPORT_SYMBOL_GPL(fat_detach); EXPORT_SYMBOL_GPL(fat_detach);
struct inode *fat_iget(struct super_block *sb, loff_t i_pos) struct inode *fat_iget(struct super_block *sb, loff_t i_pos)
{ {
struct msdos_sb_info *sbi = MSDOS_SB(sb); struct msdos_sb_info *sbi = MSDOS_SB(sb);
struct hlist_head *head = sbi->inode_hashtable + fat_hash(sb, i_pos); struct hlist_head *head = sbi->inode_hashtable + fat_hash(i_pos);
struct hlist_node *_p; struct hlist_node *_p;
struct msdos_inode_info *i; struct msdos_inode_info *i;
struct inode *inode = NULL; struct inode *inode = NULL;