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Linux/include/linux/crush/crush.h

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  1 #ifndef CEPH_CRUSH_CRUSH_H
  2 #define CEPH_CRUSH_CRUSH_H
  3 
  4 #ifdef __KERNEL__
  5 # include <linux/types.h>
  6 #else
  7 # include "crush_compat.h"
  8 #endif
  9 
 10 /*
 11  * CRUSH is a pseudo-random data distribution algorithm that
 12  * efficiently distributes input values (typically, data objects)
 13  * across a heterogeneous, structured storage cluster.
 14  *
 15  * The algorithm was originally described in detail in this paper
 16  * (although the algorithm has evolved somewhat since then):
 17  *
 18  *     http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
 19  *
 20  * LGPL2
 21  */
 22 
 23 
 24 #define CRUSH_MAGIC 0x00010000ul   /* for detecting algorithm revisions */
 25 
 26 #define CRUSH_MAX_DEPTH 10  /* max crush hierarchy depth */
 27 #define CRUSH_MAX_RULESET (1<<8)  /* max crush ruleset number */
 28 #define CRUSH_MAX_RULES CRUSH_MAX_RULESET  /* should be the same as max rulesets */
 29 
 30 #define CRUSH_MAX_DEVICE_WEIGHT (100u * 0x10000u)
 31 #define CRUSH_MAX_BUCKET_WEIGHT (65535u * 0x10000u)
 32 
 33 #define CRUSH_ITEM_UNDEF  0x7ffffffe  /* undefined result (internal use only) */
 34 #define CRUSH_ITEM_NONE   0x7fffffff  /* no result */
 35 
 36 /*
 37  * CRUSH uses user-defined "rules" to describe how inputs should be
 38  * mapped to devices.  A rule consists of sequence of steps to perform
 39  * to generate the set of output devices.
 40  */
 41 struct crush_rule_step {
 42         __u32 op;
 43         __s32 arg1;
 44         __s32 arg2;
 45 };
 46 
 47 /* step op codes */
 48 enum {
 49         CRUSH_RULE_NOOP = 0,
 50         CRUSH_RULE_TAKE = 1,          /* arg1 = value to start with */
 51         CRUSH_RULE_CHOOSE_FIRSTN = 2, /* arg1 = num items to pick */
 52                                       /* arg2 = type */
 53         CRUSH_RULE_CHOOSE_INDEP = 3,  /* same */
 54         CRUSH_RULE_EMIT = 4,          /* no args */
 55         CRUSH_RULE_CHOOSELEAF_FIRSTN = 6,
 56         CRUSH_RULE_CHOOSELEAF_INDEP = 7,
 57 
 58         CRUSH_RULE_SET_CHOOSE_TRIES = 8, /* override choose_total_tries */
 59         CRUSH_RULE_SET_CHOOSELEAF_TRIES = 9, /* override chooseleaf_descend_once */
 60         CRUSH_RULE_SET_CHOOSE_LOCAL_TRIES = 10,
 61         CRUSH_RULE_SET_CHOOSE_LOCAL_FALLBACK_TRIES = 11,
 62         CRUSH_RULE_SET_CHOOSELEAF_VARY_R = 12,
 63         CRUSH_RULE_SET_CHOOSELEAF_STABLE = 13
 64 };
 65 
 66 /*
 67  * for specifying choose num (arg1) relative to the max parameter
 68  * passed to do_rule
 69  */
 70 #define CRUSH_CHOOSE_N            0
 71 #define CRUSH_CHOOSE_N_MINUS(x)   (-(x))
 72 
 73 /*
 74  * The rule mask is used to describe what the rule is intended for.
 75  * Given a ruleset and size of output set, we search through the
 76  * rule list for a matching rule_mask.
 77  */
 78 struct crush_rule_mask {
 79         __u8 ruleset;
 80         __u8 type;
 81         __u8 min_size;
 82         __u8 max_size;
 83 };
 84 
 85 struct crush_rule {
 86         __u32 len;
 87         struct crush_rule_mask mask;
 88         struct crush_rule_step steps[0];
 89 };
 90 
 91 #define crush_rule_size(len) (sizeof(struct crush_rule) + \
 92                               (len)*sizeof(struct crush_rule_step))
 93 
 94 
 95 
 96 /*
 97  * A bucket is a named container of other items (either devices or
 98  * other buckets).  Items within a bucket are chosen using one of a
 99  * few different algorithms.  The table summarizes how the speed of
100  * each option measures up against mapping stability when items are
101  * added or removed.
102  *
103  *  Bucket Alg     Speed       Additions    Removals
104  *  ------------------------------------------------
105  *  uniform         O(1)       poor         poor
106  *  list            O(n)       optimal      poor
107  *  tree            O(log n)   good         good
108  *  straw           O(n)       better       better
109  *  straw2          O(n)       optimal      optimal
110  */
111 enum {
112         CRUSH_BUCKET_UNIFORM = 1,
113         CRUSH_BUCKET_LIST = 2,
114         CRUSH_BUCKET_TREE = 3,
115         CRUSH_BUCKET_STRAW = 4,
116         CRUSH_BUCKET_STRAW2 = 5,
117 };
118 extern const char *crush_bucket_alg_name(int alg);
119 
120 /*
121  * although tree was a legacy algorithm, it has been buggy, so
122  * exclude it.
123  */
124 #define CRUSH_LEGACY_ALLOWED_BUCKET_ALGS (      \
125                 (1 << CRUSH_BUCKET_UNIFORM) |   \
126                 (1 << CRUSH_BUCKET_LIST) |      \
127                 (1 << CRUSH_BUCKET_STRAW))
128 
129 struct crush_bucket {
130         __s32 id;        /* this'll be negative */
131         __u16 type;      /* non-zero; type=0 is reserved for devices */
132         __u8 alg;        /* one of CRUSH_BUCKET_* */
133         __u8 hash;       /* which hash function to use, CRUSH_HASH_* */
134         __u32 weight;    /* 16-bit fixed point */
135         __u32 size;      /* num items */
136         __s32 *items;
137 
138         /*
139          * cached random permutation: used for uniform bucket and for
140          * the linear search fallback for the other bucket types.
141          */
142         __u32 perm_x;  /* @x for which *perm is defined */
143         __u32 perm_n;  /* num elements of *perm that are permuted/defined */
144         __u32 *perm;
145 };
146 
147 struct crush_bucket_uniform {
148         struct crush_bucket h;
149         __u32 item_weight;  /* 16-bit fixed point; all items equally weighted */
150 };
151 
152 struct crush_bucket_list {
153         struct crush_bucket h;
154         __u32 *item_weights;  /* 16-bit fixed point */
155         __u32 *sum_weights;   /* 16-bit fixed point.  element i is sum
156                                  of weights 0..i, inclusive */
157 };
158 
159 struct crush_bucket_tree {
160         struct crush_bucket h;  /* note: h.size is _tree_ size, not number of
161                                    actual items */
162         __u8 num_nodes;
163         __u32 *node_weights;
164 };
165 
166 struct crush_bucket_straw {
167         struct crush_bucket h;
168         __u32 *item_weights;   /* 16-bit fixed point */
169         __u32 *straws;         /* 16-bit fixed point */
170 };
171 
172 struct crush_bucket_straw2 {
173         struct crush_bucket h;
174         __u32 *item_weights;   /* 16-bit fixed point */
175 };
176 
177 
178 
179 /*
180  * CRUSH map includes all buckets, rules, etc.
181  */
182 struct crush_map {
183         struct crush_bucket **buckets;
184         struct crush_rule **rules;
185 
186         __s32 max_buckets;
187         __u32 max_rules;
188         __s32 max_devices;
189 
190         /* choose local retries before re-descent */
191         __u32 choose_local_tries;
192         /* choose local attempts using a fallback permutation before
193          * re-descent */
194         __u32 choose_local_fallback_tries;
195         /* choose attempts before giving up */
196         __u32 choose_total_tries;
197         /* attempt chooseleaf inner descent once for firstn mode; on
198          * reject retry outer descent.  Note that this does *not*
199          * apply to a collision: in that case we will retry as we used
200          * to. */
201         __u32 chooseleaf_descend_once;
202 
203         /* if non-zero, feed r into chooseleaf, bit-shifted right by (r-1)
204          * bits.  a value of 1 is best for new clusters.  for legacy clusters
205          * that want to limit reshuffling, a value of 3 or 4 will make the
206          * mappings line up a bit better with previous mappings. */
207         __u8 chooseleaf_vary_r;
208 
209         /* if true, it makes chooseleaf firstn to return stable results (if
210          * no local retry) so that data migrations would be optimal when some
211          * device fails. */
212         __u8 chooseleaf_stable;
213 
214 #ifndef __KERNEL__
215         /*
216          * version 0 (original) of straw_calc has various flaws.  version 1
217          * fixes a few of them.
218          */
219         __u8 straw_calc_version;
220 
221         /*
222          * allowed bucket algs is a bitmask, here the bit positions
223          * are CRUSH_BUCKET_*.  note that these are *bits* and
224          * CRUSH_BUCKET_* values are not, so we need to or together (1
225          * << CRUSH_BUCKET_WHATEVER).  The 0th bit is not used to
226          * minimize confusion (bucket type values start at 1).
227          */
228         __u32 allowed_bucket_algs;
229 
230         __u32 *choose_tries;
231 #endif
232 };
233 
234 
235 /* crush.c */
236 extern int crush_get_bucket_item_weight(const struct crush_bucket *b, int pos);
237 extern void crush_destroy_bucket_uniform(struct crush_bucket_uniform *b);
238 extern void crush_destroy_bucket_list(struct crush_bucket_list *b);
239 extern void crush_destroy_bucket_tree(struct crush_bucket_tree *b);
240 extern void crush_destroy_bucket_straw(struct crush_bucket_straw *b);
241 extern void crush_destroy_bucket_straw2(struct crush_bucket_straw2 *b);
242 extern void crush_destroy_bucket(struct crush_bucket *b);
243 extern void crush_destroy_rule(struct crush_rule *r);
244 extern void crush_destroy(struct crush_map *map);
245 
246 static inline int crush_calc_tree_node(int i)
247 {
248         return ((i+1) << 1)-1;
249 }
250 
251 #endif
252 

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