LXR linux/include/linux/crush/crush.h

   1#ifndef CEPH_CRUSH_CRUSH_H
   2#define CEPH_CRUSH_CRUSH_H
   3
   4#include <linux/types.h>
   5
   6/*
   7 * CRUSH is a pseudo-random data distribution algorithm that
   8 * efficiently distributes input values (typically, data objects)
   9 * across a heterogeneous, structured storage cluster.
  10 *
  11 * The algorithm was originally described in detail in this paper
  12 * (although the algorithm has evolved somewhat since then):
  13 *
  14 *     http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
  15 *
  16 * LGPL2
  17 */
  18
  19
  20#define CRUSH_MAGIC 0x00010000ul   /* for detecting algorithm revisions */
  21
  22#define CRUSH_MAX_DEPTH 10  /* max crush hierarchy depth */
  23
  24
  25#define CRUSH_ITEM_UNDEF  0x7ffffffe  /* undefined result (internal use only) */
  26#define CRUSH_ITEM_NONE   0x7fffffff  /* no result */
  27
  28/*
  29 * CRUSH uses user-defined "rules" to describe how inputs should be
  30 * mapped to devices.  A rule consists of sequence of steps to perform
  31 * to generate the set of output devices.
  32 */
  33struct crush_rule_step {
  34        __u32 op;
  35        __s32 arg1;
  36        __s32 arg2;
  37};
  38
  39/* step op codes */
  40enum {
  41        CRUSH_RULE_NOOP = 0,
  42        CRUSH_RULE_TAKE = 1,          /* arg1 = value to start with */
  43        CRUSH_RULE_CHOOSE_FIRSTN = 2, /* arg1 = num items to pick */
  44                                      /* arg2 = type */
  45        CRUSH_RULE_CHOOSE_INDEP = 3,  /* same */
  46        CRUSH_RULE_EMIT = 4,          /* no args */
  47        CRUSH_RULE_CHOOSELEAF_FIRSTN = 6,
  48        CRUSH_RULE_CHOOSELEAF_INDEP = 7,
  49
  50        CRUSH_RULE_SET_CHOOSE_TRIES = 8, /* override choose_total_tries */
  51        CRUSH_RULE_SET_CHOOSELEAF_TRIES = 9, /* override chooseleaf_descend_once */
  52        CRUSH_RULE_SET_CHOOSE_LOCAL_TRIES = 10,
  53        CRUSH_RULE_SET_CHOOSE_LOCAL_FALLBACK_TRIES = 11,
  54        CRUSH_RULE_SET_CHOOSELEAF_VARY_R = 12
  55};
  56
  57/*
  58 * for specifying choose num (arg1) relative to the max parameter
  59 * passed to do_rule
  60 */
  61#define CRUSH_CHOOSE_N            0
  62#define CRUSH_CHOOSE_N_MINUS(x)   (-(x))
  63
  64/*
  65 * The rule mask is used to describe what the rule is intended for.
  66 * Given a ruleset and size of output set, we search through the
  67 * rule list for a matching rule_mask.
  68 */
  69struct crush_rule_mask {
  70        __u8 ruleset;
  71        __u8 type;
  72        __u8 min_size;
  73        __u8 max_size;
  74};
  75
  76struct crush_rule {
  77        __u32 len;
  78        struct crush_rule_mask mask;
  79        struct crush_rule_step steps[0];
  80};
  81
  82#define crush_rule_size(len) (sizeof(struct crush_rule) + \
  83                              (len)*sizeof(struct crush_rule_step))
  84
  85
  86
  87/*
  88 * A bucket is a named container of other items (either devices or
  89 * other buckets).  Items within a bucket are chosen using one of a
  90 * few different algorithms.  The table summarizes how the speed of
  91 * each option measures up against mapping stability when items are
  92 * added or removed.
  93 *
  94 *  Bucket Alg     Speed       Additions    Removals
  95 *  ------------------------------------------------
  96 *  uniform         O(1)       poor         poor
  97 *  list            O(n)       optimal      poor
  98 *  tree            O(log n)   good         good
  99 *  straw           O(n)       optimal      optimal
 100 */
 101enum {
 102        CRUSH_BUCKET_UNIFORM = 1,
 103        CRUSH_BUCKET_LIST = 2,
 104        CRUSH_BUCKET_TREE = 3,
 105        CRUSH_BUCKET_STRAW = 4
 106};
 107extern const char *crush_bucket_alg_name(int alg);
 108
 109struct crush_bucket {
 110        __s32 id;        /* this'll be negative */
 111        __u16 type;      /* non-zero; type=0 is reserved for devices */
 112        __u8 alg;        /* one of CRUSH_BUCKET_* */
 113        __u8 hash;       /* which hash function to use, CRUSH_HASH_* */
 114        __u32 weight;    /* 16-bit fixed point */
 115        __u32 size;      /* num items */
 116        __s32 *items;
 117
 118        /*
 119         * cached random permutation: used for uniform bucket and for
 120         * the linear search fallback for the other bucket types.
 121         */
 122        __u32 perm_x;  /* @x for which *perm is defined */
 123        __u32 perm_n;  /* num elements of *perm that are permuted/defined */
 124        __u32 *perm;
 125};
 126
 127struct crush_bucket_uniform {
 128        struct crush_bucket h;
 129        __u32 item_weight;  /* 16-bit fixed point; all items equally weighted */
 130};
 131
 132struct crush_bucket_list {
 133        struct crush_bucket h;
 134        __u32 *item_weights;  /* 16-bit fixed point */
 135        __u32 *sum_weights;   /* 16-bit fixed point.  element i is sum
 136                                 of weights 0..i, inclusive */
 137};
 138
 139struct crush_bucket_tree {
 140        struct crush_bucket h;  /* note: h.size is _tree_ size, not number of
 141                                   actual items */
 142        __u8 num_nodes;
 143        __u32 *node_weights;
 144};
 145
 146struct crush_bucket_straw {
 147        struct crush_bucket h;
 148        __u32 *item_weights;   /* 16-bit fixed point */
 149        __u32 *straws;         /* 16-bit fixed point */
 150};
 151
 152
 153
 154/*
 155 * CRUSH map includes all buckets, rules, etc.
 156 */
 157struct crush_map {
 158        struct crush_bucket **buckets;
 159        struct crush_rule **rules;
 160
 161        __s32 max_buckets;
 162        __u32 max_rules;
 163        __s32 max_devices;
 164
 165        /* choose local retries before re-descent */
 166        __u32 choose_local_tries;
 167        /* choose local attempts using a fallback permutation before
 168         * re-descent */
 169        __u32 choose_local_fallback_tries;
 170        /* choose attempts before giving up */ 
 171        __u32 choose_total_tries;
 172        /* attempt chooseleaf inner descent once for firstn mode; on
 173         * reject retry outer descent.  Note that this does *not*
 174         * apply to a collision: in that case we will retry as we used
 175         * to. */
 176        __u32 chooseleaf_descend_once;
 177
 178        /* if non-zero, feed r into chooseleaf, bit-shifted right by (r-1)
 179         * bits.  a value of 1 is best for new clusters.  for legacy clusters
 180         * that want to limit reshuffling, a value of 3 or 4 will make the
 181         * mappings line up a bit better with previous mappings. */
 182        __u8 chooseleaf_vary_r;
 183};
 184
 185
 186/* crush.c */
 187extern int crush_get_bucket_item_weight(const struct crush_bucket *b, int pos);
 188extern void crush_destroy_bucket_uniform(struct crush_bucket_uniform *b);
 189extern void crush_destroy_bucket_list(struct crush_bucket_list *b);
 190extern void crush_destroy_bucket_tree(struct crush_bucket_tree *b);
 191extern void crush_destroy_bucket_straw(struct crush_bucket_straw *b);
 192extern void crush_destroy_bucket(struct crush_bucket *b);
 193extern void crush_destroy_rule(struct crush_rule *r);
 194extern void crush_destroy(struct crush_map *map);
 195
 196static inline int crush_calc_tree_node(int i)
 197{
 198        return ((i+1) << 1)-1;
 199}
 200
 201#endif
 202