Commit d3dfa822 authored by OGAWA Hirofumi's avatar OGAWA Hirofumi Committed by Linus Torvalds
Browse files

fat: improve fat_hash() 



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: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 52e9d9f4

fs/fat/fat.h

+0 −1
Original line number Diff line number Diff line
@@ -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

fs/fat/inode.c

+7 −11
Original line number Diff line number Diff line
@@ -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_block *sb) 
		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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