Messages in this thread Patch in this message | | | Subject | [PATCH 07/21] fat: improve fat_hash() | From | OGAWA Hirofumi <> | Date | Wed, 15 Oct 2008 22:57:58 +0900 |
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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> ---
fs/fat/fat.h | 1 - fs/fat/inode.c | 18 +++++++----------- 2 files changed, 7 insertions(+), 12 deletions(-)
diff -puN fs/fat/fat.h~fat_improve-hash fs/fat/fat.h --- linux-2.6/fs/fat/fat.h~fat_improve-hash 2008-08-25 03:33:31.000000000 +0900 +++ linux-2.6-hirofumi/fs/fat/fat.h 2008-08-25 03:50:16.000000000 +0900 @@ -43,7 +43,6 @@ struct fat_mount_options { #define FAT_HASH_BITS 8 #define FAT_HASH_SIZE (1UL << FAT_HASH_BITS) -#define FAT_HASH_MASK (FAT_HASH_SIZE-1) /* * MS-DOS file system in-core superblock data diff -puN fs/fat/inode.c~fat_improve-hash fs/fat/inode.c --- linux-2.6/fs/fat/inode.c~fat_improve-hash 2008-08-25 03:33:31.000000000 +0900 +++ linux-2.6-hirofumi/fs/fat/inode.c 2008-08-25 03:50:16.000000000 +0900 @@ -26,6 +26,7 @@ #include <linux/uio.h> #include <linux/writeback.h> #include <linux/log2.h> +#include <linux/hash.h> #include <asm/unaligned.h> #include "fat.h" @@ -247,25 +248,21 @@ static void fat_hash_init(struct super_b 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; - tmp = tmp + (tmp >> FAT_HASH_BITS) + (tmp >> FAT_HASH_BITS * 2); - return tmp & FAT_HASH_MASK; + return hash_32(i_pos, FAT_HASH_BITS); } void fat_attach(struct inode *inode, loff_t i_pos) { - struct super_block *sb = inode->i_sb; - struct msdos_sb_info *sbi = MSDOS_SB(sb); + struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb); + struct hlist_head *head = sbi->inode_hashtable + fat_hash(i_pos); spin_lock(&sbi->inode_hash_lock); MSDOS_I(inode)->i_pos = i_pos; - hlist_add_head(&MSDOS_I(inode)->i_fat_hash, - sbi->inode_hashtable + fat_hash(sb, i_pos)); + hlist_add_head(&MSDOS_I(inode)->i_fat_hash, head); spin_unlock(&sbi->inode_hash_lock); } - EXPORT_SYMBOL_GPL(fat_attach); 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); spin_unlock(&sbi->inode_hash_lock); } - EXPORT_SYMBOL_GPL(fat_detach); struct inode *fat_iget(struct super_block *sb, loff_t i_pos) { 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 msdos_inode_info *i; struct inode *inode = NULL; _
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