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  */
  33 struct crush_rule_step {
  34         __u32 op;
  35         __s32 arg1;
  36         __s32 arg2;
  37 };
  38
  39 /* step op codes */
  40 enum {
  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 };
  55
  56 /*
  57  * for specifying choose num (arg1) relative to the max parameter
  58  * passed to do_rule
  59  */
  60 #define CRUSH_CHOOSE_N            0
  61 #define CRUSH_CHOOSE_N_MINUS(x)   (-(x))
  62
  63 /*
  64  * The rule mask is used to describe what the rule is intended for.
  65  * Given a ruleset and size of output set, we search through the
  66  * rule list for a matching rule_mask.
  67  */
  68 struct crush_rule_mask {
  69         __u8 ruleset;
  70         __u8 type;
  71         __u8 min_size;
  72         __u8 max_size;
  73 };
  74
  75 struct crush_rule {
  76         __u32 len;
  77         struct crush_rule_mask mask;
  78         struct crush_rule_step steps[0];
  79 };
  80
  81 #define crush_rule_size(len) (sizeof(struct crush_rule) + \
  82                               (len)*sizeof(struct crush_rule_step))
  83
  84
  85
  86 /*
  87  * A bucket is a named container of other items (either devices or
  88  * other buckets).  Items within a bucket are chosen using one of a
  89  * few different algorithms.  The table summarizes how the speed of
  90  * each option measures up against mapping stability when items are
  91  * added or removed.
  92  *
  93  *  Bucket Alg     Speed       Additions    Removals
  94  *  ------------------------------------------------
  95  *  uniform         O(1)       poor         poor
  96  *  list            O(n)       optimal      poor
  97  *  tree            O(log n)   good         good
  98  *  straw           O(n)       optimal      optimal
  99  */
 100 enum {
 101         CRUSH_BUCKET_UNIFORM = 1,
 102         CRUSH_BUCKET_LIST = 2,
 103         CRUSH_BUCKET_TREE = 3,
 104         CRUSH_BUCKET_STRAW = 4
 105 };
 106 extern const char *crush_bucket_alg_name(int alg);
 107
 108 struct crush_bucket {
 109         __s32 id;        /* this'll be negative */
 110         __u16 type;      /* non-zero; type=0 is reserved for devices */
 111         __u8 alg;        /* one of CRUSH_BUCKET_* */
 112         __u8 hash;       /* which hash function to use, CRUSH_HASH_* */
 113         __u32 weight;    /* 16-bit fixed point */
 114         __u32 size;      /* num items */
 115         __s32 *items;
 116
 117         /*
 118          * cached random permutation: used for uniform bucket and for
 119          * the linear search fallback for the other bucket types.
 120          */
 121         __u32 perm_x;  /* @x for which *perm is defined */
 122         __u32 perm_n;  /* num elements of *perm that are permuted/defined */
 123         __u32 *perm;
 124 };
 125
 126 struct crush_bucket_uniform {
 127         struct crush_bucket h;
 128         __u32 item_weight;  /* 16-bit fixed point; all items equally weighted */
 129 };
 130
 131 struct crush_bucket_list {
 132         struct crush_bucket h;
 133         __u32 *item_weights;  /* 16-bit fixed point */
 134         __u32 *sum_weights;   /* 16-bit fixed point.  element i is sum
 135                                  of weights 0..i, inclusive */
 136 };
 137
 138 struct crush_bucket_tree {
 139         struct crush_bucket h;  /* note: h.size is _tree_ size, not number of
 140                                    actual items */
 141         __u8 num_nodes;
 142         __u32 *node_weights;
 143 };
 144
 145 struct crush_bucket_straw {
 146         struct crush_bucket h;
 147         __u32 *item_weights;   /* 16-bit fixed point */
 148         __u32 *straws;         /* 16-bit fixed point */
 149 };
 150
 151
 152
 153 /*
 154  * CRUSH map includes all buckets, rules, etc.
 155  */
 156 struct crush_map {
 157         struct crush_bucket **buckets;
 158         struct crush_rule **rules;
 159
 160         __s32 max_buckets;
 161         __u32 max_rules;
 162         __s32 max_devices;
 163
 164         /* choose local retries before re-descent */
 165         __u32 choose_local_tries;
 166         /* choose local attempts using a fallback permutation before
 167          * re-descent */
 168         __u32 choose_local_fallback_tries;
 169         /* choose attempts before giving up */
 170         __u32 choose_total_tries;
 171         /* attempt chooseleaf inner descent once for firstn mode; on
 172          * reject retry outer descent.  Note that this does *not*
 173          * apply to a collision: in that case we will retry as we used
 174          * to. */
 175         __u32 chooseleaf_descend_once;
 176 };
 177
 178
 179 /* crush.c */
 180 extern int crush_get_bucket_item_weight(const struct crush_bucket *b, int pos);
 181 extern void crush_destroy_bucket_uniform(struct crush_bucket_uniform *b);
 182 extern void crush_destroy_bucket_list(struct crush_bucket_list *b);
 183 extern void crush_destroy_bucket_tree(struct crush_bucket_tree *b);
 184 extern void crush_destroy_bucket_straw(struct crush_bucket_straw *b);
 185 extern void crush_destroy_bucket(struct crush_bucket *b);
 186 extern void crush_destroy_rule(struct crush_rule *r);
 187 extern void crush_destroy(struct crush_map *map);
 188
 189 static inline int crush_calc_tree_node(int i)
 190 {
 191         return ((i+1) << 1)-1;
 192 }
 193
 194 #endif