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
  23 #define CRUSH_MAX_DEPTH 10  /* max crush hierarchy depth */
  24 #define CRUSH_MAX_SET   10  /* max size of a mapping result */
  25
  26
  27 /*
  28  * CRUSH uses user-defined "rules" to describe how inputs should be
  29  * mapped to devices.  A rule consists of sequence of steps to perform
  30  * to generate the set of output devices.
  31  */
  32 struct crush_rule_step {
  33         __u32 op;
  34         __s32 arg1;
  35         __s32 arg2;
  36 };
  37
  38 /* step op codes */
  39 enum {
  40         CRUSH_RULE_NOOP = 0,
  41         CRUSH_RULE_TAKE = 1,          /* arg1 = value to start with */
  42         CRUSH_RULE_CHOOSE_FIRSTN = 2, /* arg1 = num items to pick */
  43                                       /* arg2 = type */
  44         CRUSH_RULE_CHOOSE_INDEP = 3,  /* same */
  45         CRUSH_RULE_EMIT = 4,          /* no args */
  46         CRUSH_RULE_CHOOSE_LEAF_FIRSTN = 6,
  47         CRUSH_RULE_CHOOSE_LEAF_INDEP = 7,
  48 };
  49
  50 /*
  51  * for specifying choose num (arg1) relative to the max parameter
  52  * passed to do_rule
  53  */
  54 #define CRUSH_CHOOSE_N            0
  55 #define CRUSH_CHOOSE_N_MINUS(x)   (-(x))
  56
  57 /*
  58  * The rule mask is used to describe what the rule is intended for.
  59  * Given a ruleset and size of output set, we search through the
  60  * rule list for a matching rule_mask.
  61  */
  62 struct crush_rule_mask {
  63         __u8 ruleset;
  64         __u8 type;
  65         __u8 min_size;
  66         __u8 max_size;
  67 };
  68
  69 struct crush_rule {
  70         __u32 len;
  71         struct crush_rule_mask mask;
  72         struct crush_rule_step steps[0];
  73 };
  74
  75 #define crush_rule_size(len) (sizeof(struct crush_rule) + \
  76                               (len)*sizeof(struct crush_rule_step))
  77
  78
  79
  80 /*
  81  * A bucket is a named container of other items (either devices or
  82  * other buckets).  Items within a bucket are chosen using one of a
  83  * few different algorithms.  The table summarizes how the speed of
  84  * each option measures up against mapping stability when items are
  85  * added or removed.
  86  *
  87  *  Bucket Alg     Speed       Additions    Removals
  88  *  ------------------------------------------------
  89  *  uniform         O(1)       poor         poor
  90  *  list            O(n)       optimal      poor
  91  *  tree            O(log n)   good         good
  92  *  straw           O(n)       optimal      optimal
  93  */
  94 enum {
  95         CRUSH_BUCKET_UNIFORM = 1,
  96         CRUSH_BUCKET_LIST = 2,
  97         CRUSH_BUCKET_TREE = 3,
  98         CRUSH_BUCKET_STRAW = 4
  99 };
 100 extern const char *crush_bucket_alg_name(int alg);
 101
 102 struct crush_bucket {
 103         __s32 id;        /* this'll be negative */
 104         __u16 type;      /* non-zero; type=0 is reserved for devices */
 105         __u8 alg;        /* one of CRUSH_BUCKET_* */
 106         __u8 hash;       /* which hash function to use, CRUSH_HASH_* */
 107         __u32 weight;    /* 16-bit fixed point */
 108         __u32 size;      /* num items */
 109         __s32 *items;
 110
 111         /*
 112          * cached random permutation: used for uniform bucket and for
 113          * the linear search fallback for the other bucket types.
 114          */
 115         __u32 perm_x;  /* @x for which *perm is defined */
 116         __u32 perm_n;  /* num elements of *perm that are permuted/defined */
 117         __u32 *perm;
 118 };
 119
 120 struct crush_bucket_uniform {
 121         struct crush_bucket h;
 122         __u32 item_weight;  /* 16-bit fixed point; all items equally weighted */
 123 };
 124
 125 struct crush_bucket_list {
 126         struct crush_bucket h;
 127         __u32 *item_weights;  /* 16-bit fixed point */
 128         __u32 *sum_weights;   /* 16-bit fixed point.  element i is sum
 129                                  of weights 0..i, inclusive */
 130 };
 131
 132 struct crush_bucket_tree {
 133         struct crush_bucket h;  /* note: h.size is _tree_ size, not number of
 134                                    actual items */
 135         __u8 num_nodes;
 136         __u32 *node_weights;
 137 };
 138
 139 struct crush_bucket_straw {
 140         struct crush_bucket h;
 141         __u32 *item_weights;   /* 16-bit fixed point */
 142         __u32 *straws;         /* 16-bit fixed point */
 143 };
 144
 145
 146
 147 /*
 148  * CRUSH map includes all buckets, rules, etc.
 149  */
 150 struct crush_map {
 151         struct crush_bucket **buckets;
 152         struct crush_rule **rules;
 153
 154         /*
 155          * Parent pointers to identify the parent bucket a device or
 156          * bucket in the hierarchy.  If an item appears more than
 157          * once, this is the _last_ time it appeared (where buckets
 158          * are processed in bucket id order, from -1 on down to
 159          * -max_buckets.
 160          */
 161         __u32 *bucket_parents;
 162         __u32 *device_parents;
 163
 164         __s32 max_buckets;
 165         __u32 max_rules;
 166         __s32 max_devices;
 167 };
 168
 169
 170 /* crush.c */
 171 extern int crush_get_bucket_item_weight(struct crush_bucket *b, int pos);
 172 extern void crush_calc_parents(struct crush_map *map);
 173 extern void crush_destroy_bucket_uniform(struct crush_bucket_uniform *b);
 174 extern void crush_destroy_bucket_list(struct crush_bucket_list *b);
 175 extern void crush_destroy_bucket_tree(struct crush_bucket_tree *b);
 176 extern void crush_destroy_bucket_straw(struct crush_bucket_straw *b);
 177 extern void crush_destroy_bucket(struct crush_bucket *b);
 178 extern void crush_destroy(struct crush_map *map);
 179
 180 #endif