dirhash.h revision 262779 
1/*-
2 * Copyright (c) 2001 Ian Dowse.  All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23 * SUCH DAMAGE.
24 *
25 * $FreeBSD: stable/10/sys/ufs/ufs/dirhash.h 262779 2014-03-05 04:23:19Z pfg $
26 */
27
28#ifndef _UFS_UFS_DIRHASH_H_
29#define	_UFS_UFS_DIRHASH_H_
30
31#include <sys/_lock.h>
32#include <sys/_sx.h>
33
34/*
35 * For fast operations on large directories, we maintain a hash
36 * that maps the file name to the offset of the directory entry within
37 * the directory file.
38 *
39 * The hashing uses a dumb spillover to the next free slot on
40 * collisions, so we must keep the utilisation low to avoid
41 * long linear searches. Deleted entries that are not the last
42 * in a chain must be marked DIRHASH_DEL.
43 *
44 * We also maintain information about free space in each block
45 * to speed up creations.
46 */
47#define	DIRHASH_EMPTY	(-1)	/* entry unused */
48#define	DIRHASH_DEL	(-2)	/* deleted entry; may be part of chain */
49
50#define	DIRALIGN	4
51#define	DH_NFSTATS	(DIRECTSIZ(MAXNAMLEN + 1) / DIRALIGN)
52				 /* max DIRALIGN words in a directory entry */
53
54/*
55 * Dirhash uses a score mechanism to achieve a hybrid between a
56 * least-recently-used and a least-often-used algorithm for entry
57 * recycling. The score is incremented when a directory is used, and
58 * decremented when the directory is a candidate for recycling. When
59 * the score reaches zero, the hash is recycled. Hashes are linked
60 * together on a TAILQ list, and hashes with higher scores filter
61 * towards the tail (most recently used) end of the list.
62 *
63 * New hash entries are given an inital score of DH_SCOREINIT and are
64 * placed at the most-recently-used end of the list. This helps a lot
65 * in the worst-case case scenario where every directory access is
66 * to a directory that is not hashed (i.e. the working set of hash
67 * candidates is much larger than the configured memry limit). In this
68 * case it limits the number of hash builds to 1/DH_SCOREINIT of the
69 * number of accesses.
70 */
71#define	DH_SCOREINIT	8	/* initial dh_score when dirhash built */
72#define	DH_SCOREMAX	64	/* max dh_score value */
73
74/*
75 * The main hash table has 2 levels. It is an array of pointers to
76 * blocks of DH_NBLKOFF offsets.
77 */
78#define	DH_BLKOFFSHIFT	8
79#define	DH_NBLKOFF	(1 << DH_BLKOFFSHIFT)
80#define	DH_BLKOFFMASK	(DH_NBLKOFF - 1)
81
82#define	DH_ENTRY(dh, slot) \
83    ((dh)->dh_hash[(slot) >> DH_BLKOFFSHIFT][(slot) & DH_BLKOFFMASK])
84
85struct dirhash {
86	struct sx dh_lock;	/* protects all fields except list & score */
87	int	dh_refcount;
88
89	doff_t	**dh_hash;	/* the hash array (2-level) */
90	int	dh_narrays;	/* number of entries in dh_hash */
91	int	dh_hlen;	/* total slots in the 2-level hash array */
92	int	dh_hused;	/* entries in use */
93	int	dh_memreq;	/* Memory used. */
94
95	/* Free space statistics. XXX assumes DIRBLKSIZ is 512. */
96	u_int8_t *dh_blkfree;	/* free DIRALIGN words in each dir block */
97	int	dh_nblk;	/* size of dh_blkfree array */
98	int	dh_dirblks;	/* number of DIRBLKSIZ blocks in dir */
99	int	dh_firstfree[DH_NFSTATS + 1]; /* first blk with N words free */
100
101	doff_t	dh_seqoff;	/* sequential access optimisation offset */
102
103	int	dh_score;	/* access count for this dirhash */
104
105	int	dh_onlist;	/* true if on the ufsdirhash_list chain */
106
107	time_t	dh_lastused;	/* time the dirhash was last read or written*/
108
109	/* Protected by ufsdirhash_mtx. */
110	TAILQ_ENTRY(dirhash) dh_list;	/* chain of all dirhashes */
111};
112
113
114/*
115 * Dirhash functions.
116 */
117void	ufsdirhash_init(void);
118void	ufsdirhash_uninit(void);
119int	ufsdirhash_build(struct inode *);
120doff_t	ufsdirhash_findfree(struct inode *, int, int *);
121doff_t	ufsdirhash_enduseful(struct inode *);
122int	ufsdirhash_lookup(struct inode *, char *, int, doff_t *, struct buf **,
123	    doff_t *);
124void	ufsdirhash_newblk(struct inode *, doff_t);
125void	ufsdirhash_add(struct inode *, struct direct *, doff_t);
126void	ufsdirhash_remove(struct inode *, struct direct *, doff_t);
127void	ufsdirhash_move(struct inode *, struct direct *, doff_t, doff_t);
128void	ufsdirhash_dirtrunc(struct inode *, doff_t);
129void	ufsdirhash_free(struct inode *);
130
131void	ufsdirhash_checkblock(struct inode *, char *, doff_t);
132
133#endif /* !_UFS_UFS_DIRHASH_H_ */
134