Annotation of sys/ufs/ufs/dirhash.h, Revision 1.1.1.1
1.1 nbrk 1: /* $OpenBSD: dirhash.h,v 1.4 2006/04/29 23:09:45 tedu Exp $ */
2: /*
3: * Copyright (c) 2001 Ian Dowse. All rights reserved.
4: *
5: * Redistribution and use in source and binary forms, with or without
6: * modification, are permitted provided that the following conditions
7: * are met:
8: * 1. Redistributions of source code must retain the above copyright
9: * notice, this list of conditions and the following disclaimer.
10: * 2. Redistributions in binary form must reproduce the above copyright
11: * notice, this list of conditions and the following disclaimer in the
12: * documentation and/or other materials provided with the distribution.
13: *
14: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17: * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24: * SUCH DAMAGE.
25: *
26: * $FreeBSD: src/sys/ufs/ufs/dirhash.h,v 1.4 2003/01/01 18:48:59 schweikh Exp $
27: */
28:
29: #ifndef _UFS_UFS_DIRHASH_H_
30: #define _UFS_UFS_DIRHASH_H_
31:
32: #include <sys/rwlock.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:
85: struct dirhash {
86: doff_t **dh_hash; /* the hash array (2-level) */
87: int dh_narrays; /* number of entries in dh_hash */
88: int dh_hlen; /* total slots in the 2-level hash array */
89: int dh_hused; /* entries in use */
90:
91: /* Free space statistics. XXX assumes DIRBLKSIZ is 512. */
92: u_int8_t *dh_blkfree; /* free DIRALIGN words in each dir block */
93: int dh_nblk; /* size of dh_blkfree array */
94: int dh_dirblks; /* number of DIRBLKSIZ blocks in dir */
95: int dh_firstfree[DH_NFSTATS + 1]; /* first blk with N words free */
96:
97: int dh_seqopt; /* sequential access optimisation enabled */
98: doff_t dh_seqoff; /* sequential access optimisation offset */
99:
100: int dh_score; /* access count for this dirhash */
101:
102: int dh_onlist; /* true if on the ufsdirhash_list chain */
103:
104: /* Protected by ufsdirhash_mtx. */
105: TAILQ_ENTRY(dirhash) dh_list; /* chain of all dirhashes */
106: };
107:
108: extern int ufs_mindirhashsize;
109: extern int ufs_dirhashmaxmem;
110: extern int ufs_dirhashmem;
111:
112: /*
113: * Dirhash functions.
114: */
115: void ufsdirhash_init(void);
116: void ufsdirhash_uninit(void);
117: int ufsdirhash_build(struct inode *);
118: doff_t ufsdirhash_findfree(struct inode *, int, int *);
119: doff_t ufsdirhash_enduseful(struct inode *);
120: int ufsdirhash_lookup(struct inode *, char *, int, doff_t *, struct buf **,
121: doff_t *);
122: void ufsdirhash_newblk(struct inode *, doff_t);
123: void ufsdirhash_add(struct inode *, struct direct *, doff_t);
124: void ufsdirhash_remove(struct inode *, struct direct *, doff_t);
125: void ufsdirhash_move(struct inode *, struct direct *, doff_t, doff_t);
126: void ufsdirhash_dirtrunc(struct inode *, doff_t);
127: void ufsdirhash_free(struct inode *);
128:
129: void ufsdirhash_checkblock(struct inode *, char *, doff_t);
130:
131: #endif /* !_UFS_UFS_DIRHASH_H_ */
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