sys/vfs/ufs/dirhash.h

   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: src/sys/ufs/ufs/dirhash.h,v 1.2.2.1 2001/08/01 19:33:39 iedowse Exp $
  26  * $DragonFly: src/sys/vfs/ufs/dirhash.h,v 1.4 2006/04/03 02:02:37 dillon Exp $
  27  */
  28
  29 #ifndef _VFS_UFS_DIRHASH_H_
  30 #define _VFS_UFS_DIRHASH_H_
  31
  32 /*
  33  * XXX DR: On the current directory hashing method; the performance
  34  * on large directories is awful due to the lookup code path.
  35  */
  36 /*
  37  * For fast operations on large directories, we maintain a hash
  38  * that maps the file name to the offset of the directory entry within
  39  * the directory file.
  40  *
  41  * The hashing uses a dumb spillover to the next free slot on
  42  * collisions, so we must keep the utilisation low to avoid
  43  * long linear searches. Deleted entries that are not the last
  44  * in a chain must be marked DIRHASH_DEL.
  45  *
  46  * We also maintain a information about free space in each block
  47  * to speed up creations.
  48  */
  49 #define DIRHASH_EMPTY   (-1)    /* entry unused */
  50 #define DIRHASH_DEL     (-2)    /* deleted entry; may be part of chain */
  51
  52 #define DIRALIGN        4
  53 #define DH_NFSTATS      (DIRECTSIZ(MAXNAMLEN + 1) / DIRALIGN)
  54                                  /* max DIRALIGN words in a directory entry */
  55
  56 /*
  57  * Dirhash uses a score mechanism to achieve a hybrid between a
  58  * least-recently-used and a least-often-used algorithm for entry
  59  * recycling. The score is incremented when a directory is used, and
  60  * decremented when the directory is a candidate for recycling. When
  61  * the score reaches zero, the hash is recycled. Hashes are linked
  62  * together on a TAILQ list, and hashes with higher scores filter
  63  * towards the tail (most recently used) end of the list.
  64  *
  65  * New hash entries are given an inital score of DH_SCOREINIT and are
  66  * placed at the most-recently-used end of the list. This helps a lot
  67  * in the worst-case case scenario where every directory access is
  68  * to a directory that is not hashed (i.e. the working set of hash
  69  * candidates is much larger than the configured memry limit). In this
  70  * case it limits the number of hash builds to 1/DH_SCOREINIT of the
  71  * number of accesses.
  72  */
  73 #define DH_SCOREINIT    8       /* initial dh_score when dirhash built */
  74 #define DH_SCOREMAX     64      /* max dh_score value */
  75
  76 /*
  77  * The main hash table has 2 levels. It is an array of pointers to
  78  * blocks of DH_NBLKOFF offsets.
  79  */
  80 #define DH_BLKOFFSHIFT  8
  81 #define DH_NBLKOFF      (1 << DH_BLKOFFSHIFT)
  82 #define DH_BLKOFFMASK   (DH_NBLKOFF - 1)
  83
  84 #define DH_ENTRY(dh, slot) \
  85     ((dh)->dh_hash[(slot) >> DH_BLKOFFSHIFT][(slot) & DH_BLKOFFMASK])
  86
  87 struct dirhash {
  88         doff_t  **dh_hash;      /* the hash array (2-level) */
  89         int     dh_narrays;     /* number of entries in dh_hash */
  90         int     dh_hlen;        /* total slots in the 2-level hash array */
  91         int     dh_hused;       /* entries in use */
  92
  93         /* Free space statistics. XXX assumes DIRBLKSIZ is 512. */
  94         u_int8_t *dh_blkfree;   /* free DIRALIGN words in each dir block */
  95         int     dh_nblk;        /* size of dh_blkfree array */
  96         int     dh_dirblks;     /* number of DIRBLKSIZ blocks in dir */
  97         int     dh_firstfree[DH_NFSTATS + 1]; /* first blk with N words free */
  98
  99         int     dh_seqopt;      /* sequential access optimisation enabled */
 100         doff_t  dh_seqoff;      /* sequential access optimisation offset */
 101
 102         int     dh_score;       /* access count for this dirhash */
 103
 104         int     dh_onlist;      /* true if on the ufsdirhash_list chain */
 105
 106         TAILQ_ENTRY(dirhash) dh_list;   /* chain of all dirhashes */
 107 };
 108
 109
 110 /*
 111  * Dirhash functions.
 112  */
 113 int     ufsdirhash_build(struct inode *);
 114 doff_t  ufsdirhash_findfree(struct inode *, int, int *);
 115 doff_t  ufsdirhash_enduseful(struct inode *);
 116 int     ufsdirhash_lookup(struct inode *, char *, int, doff_t *, struct buf **,
 117             doff_t *);
 118 void    ufsdirhash_newblk(struct inode *, doff_t);
 119 void    ufsdirhash_add(struct inode *, struct direct *, doff_t);
 120 void    ufsdirhash_remove(struct inode *, struct direct *, doff_t);
 121 void    ufsdirhash_move(struct inode *, struct direct *, doff_t, doff_t);
 122 void    ufsdirhash_dirtrunc(struct inode *, doff_t);
 123 void    ufsdirhash_free(struct inode *);
 124
 125 void    ufsdirhash_checkblock(struct inode *, char *, doff_t);
 126
 127 #endif /* !_VFS_UFS_DIRHASH_H_ */