1 #ifndef CEPH_CRUSH_CRUSH_H
2 #define CEPH_CRUSH_CRUSH_H
5 # include <linux/types.h>
7 # include "crush_compat.h"
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.
15 * The algorithm was originally described in detail in this paper
16 * (although the algorithm has evolved somewhat since then):
18 * http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
24 #define CRUSH_MAGIC 0x00010000ul /* for detecting algorithm revisions */
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 */
30 #define CRUSH_MAX_DEVICE_WEIGHT (100u * 0x10000u)
31 #define CRUSH_MAX_BUCKET_WEIGHT (65535u * 0x10000u)
33 #define CRUSH_ITEM_UNDEF 0x7ffffffe /* undefined result (internal use only) */
34 #define CRUSH_ITEM_NONE 0x7fffffff /* no result */
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.
41 struct crush_rule_step
{
50 CRUSH_RULE_TAKE
= 1, /* arg1 = value to start with */
51 CRUSH_RULE_CHOOSE_FIRSTN
= 2, /* arg1 = num items to pick */
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,
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
66 * for specifying choose num (arg1) relative to the max parameter
69 #define CRUSH_CHOOSE_N 0
70 #define CRUSH_CHOOSE_N_MINUS(x) (-(x))
73 * The rule mask is used to describe what the rule is intended for.
74 * Given a ruleset and size of output set, we search through the
75 * rule list for a matching rule_mask.
77 struct crush_rule_mask
{
86 struct crush_rule_mask mask
;
87 struct crush_rule_step steps
[0];
90 #define crush_rule_size(len) (sizeof(struct crush_rule) + \
91 (len)*sizeof(struct crush_rule_step))
96 * A bucket is a named container of other items (either devices or
97 * other buckets). Items within a bucket are chosen using one of a
98 * few different algorithms. The table summarizes how the speed of
99 * each option measures up against mapping stability when items are
102 * Bucket Alg Speed Additions Removals
103 * ------------------------------------------------
104 * uniform O(1) poor poor
105 * list O(n) optimal poor
106 * tree O(log n) good good
107 * straw O(n) better better
108 * straw2 O(n) optimal optimal
111 CRUSH_BUCKET_UNIFORM
= 1,
112 CRUSH_BUCKET_LIST
= 2,
113 CRUSH_BUCKET_TREE
= 3,
114 CRUSH_BUCKET_STRAW
= 4,
115 CRUSH_BUCKET_STRAW2
= 5,
117 extern const char *crush_bucket_alg_name(int alg
);
120 * although tree was a legacy algorithm, it has been buggy, so
123 #define CRUSH_LEGACY_ALLOWED_BUCKET_ALGS ( \
124 (1 << CRUSH_BUCKET_UNIFORM) | \
125 (1 << CRUSH_BUCKET_LIST) | \
126 (1 << CRUSH_BUCKET_STRAW))
128 struct crush_bucket
{
129 __s32 id
; /* this'll be negative */
130 __u16 type
; /* non-zero; type=0 is reserved for devices */
131 __u8 alg
; /* one of CRUSH_BUCKET_* */
132 __u8 hash
; /* which hash function to use, CRUSH_HASH_* */
133 __u32 weight
; /* 16-bit fixed point */
134 __u32 size
; /* num items */
138 * cached random permutation: used for uniform bucket and for
139 * the linear search fallback for the other bucket types.
141 __u32 perm_x
; /* @x for which *perm is defined */
142 __u32 perm_n
; /* num elements of *perm that are permuted/defined */
146 struct crush_bucket_uniform
{
147 struct crush_bucket h
;
148 __u32 item_weight
; /* 16-bit fixed point; all items equally weighted */
151 struct crush_bucket_list
{
152 struct crush_bucket h
;
153 __u32
*item_weights
; /* 16-bit fixed point */
154 __u32
*sum_weights
; /* 16-bit fixed point. element i is sum
155 of weights 0..i, inclusive */
158 struct crush_bucket_tree
{
159 struct crush_bucket h
; /* note: h.size is _tree_ size, not number of
165 struct crush_bucket_straw
{
166 struct crush_bucket h
;
167 __u32
*item_weights
; /* 16-bit fixed point */
168 __u32
*straws
; /* 16-bit fixed point */
171 struct crush_bucket_straw2
{
172 struct crush_bucket h
;
173 __u32
*item_weights
; /* 16-bit fixed point */
179 * CRUSH map includes all buckets, rules, etc.
182 struct crush_bucket
**buckets
;
183 struct crush_rule
**rules
;
189 /* choose local retries before re-descent */
190 __u32 choose_local_tries
;
191 /* choose local attempts using a fallback permutation before
193 __u32 choose_local_fallback_tries
;
194 /* choose attempts before giving up */
195 __u32 choose_total_tries
;
196 /* attempt chooseleaf inner descent once for firstn mode; on
197 * reject retry outer descent. Note that this does *not*
198 * apply to a collision: in that case we will retry as we used
200 __u32 chooseleaf_descend_once
;
202 /* if non-zero, feed r into chooseleaf, bit-shifted right by (r-1)
203 * bits. a value of 1 is best for new clusters. for legacy clusters
204 * that want to limit reshuffling, a value of 3 or 4 will make the
205 * mappings line up a bit better with previous mappings. */
206 __u8 chooseleaf_vary_r
;
210 * version 0 (original) of straw_calc has various flaws. version 1
211 * fixes a few of them.
213 __u8 straw_calc_version
;
216 * allowed bucket algs is a bitmask, here the bit positions
217 * are CRUSH_BUCKET_*. note that these are *bits* and
218 * CRUSH_BUCKET_* values are not, so we need to or together (1
219 * << CRUSH_BUCKET_WHATEVER). The 0th bit is not used to
220 * minimize confusion (bucket type values start at 1).
222 __u32 allowed_bucket_algs
;
230 extern int crush_get_bucket_item_weight(const struct crush_bucket
*b
, int pos
);
231 extern void crush_destroy_bucket_uniform(struct crush_bucket_uniform
*b
);
232 extern void crush_destroy_bucket_list(struct crush_bucket_list
*b
);
233 extern void crush_destroy_bucket_tree(struct crush_bucket_tree
*b
);
234 extern void crush_destroy_bucket_straw(struct crush_bucket_straw
*b
);
235 extern void crush_destroy_bucket_straw2(struct crush_bucket_straw2
*b
);
236 extern void crush_destroy_bucket(struct crush_bucket
*b
);
237 extern void crush_destroy_rule(struct crush_rule
*r
);
238 extern void crush_destroy(struct crush_map
*map
);
240 static inline int crush_calc_tree_node(int i
)
242 return ((i
+1) << 1)-1;