xref: /linux/include/linux/crush/crush.h (revision cbecf716ca618fd44feda6bd9a64a8179d031fc5)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef CEPH_CRUSH_CRUSH_H
3 #define CEPH_CRUSH_CRUSH_H
4 
5 #ifdef __KERNEL__
6 # include <linux/rbtree.h>
7 # include <linux/types.h>
8 #else
9 # include "crush_compat.h"
10 #endif
11 
12 /*
13  * CRUSH is a pseudo-random data distribution algorithm that
14  * efficiently distributes input values (typically, data objects)
15  * across a heterogeneous, structured storage cluster.
16  *
17  * The algorithm was originally described in detail in this paper
18  * (although the algorithm has evolved somewhat since then):
19  *
20  *     https://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
21  *
22  * LGPL2
23  */
24 
25 
26 #define CRUSH_MAGIC 0x00010000ul   /* for detecting algorithm revisions */
27 
28 #define CRUSH_MAX_DEPTH 10  /* max crush hierarchy depth */
29 #define CRUSH_MAX_RULESET (1<<8)  /* max crush ruleset number */
30 #define CRUSH_MAX_RULES CRUSH_MAX_RULESET  /* should be the same as max rulesets */
31 
32 #define CRUSH_MAX_DEVICE_WEIGHT (100u * 0x10000u)
33 #define CRUSH_MAX_BUCKET_WEIGHT (65535u * 0x10000u)
34 
35 #define CRUSH_ITEM_UNDEF  0x7ffffffe  /* undefined result (internal use only) */
36 #define CRUSH_ITEM_NONE   0x7fffffff  /* no result */
37 
38 /*
39  * CRUSH uses user-defined "rules" to describe how inputs should be
40  * mapped to devices.  A rule consists of sequence of steps to perform
41  * to generate the set of output devices.
42  */
43 struct crush_rule_step {
44 	__u32 op;
45 	__s32 arg1;
46 	__s32 arg2;
47 };
48 
49 /* step op codes */
50 enum {
51 	CRUSH_RULE_NOOP = 0,
52 	CRUSH_RULE_TAKE = 1,          /* arg1 = value to start with */
53 	CRUSH_RULE_CHOOSE_FIRSTN = 2, /* arg1 = num items to pick */
54 				      /* arg2 = type */
55 	CRUSH_RULE_CHOOSE_INDEP = 3,  /* same */
56 	CRUSH_RULE_EMIT = 4,          /* no args */
57 	CRUSH_RULE_CHOOSELEAF_FIRSTN = 6,
58 	CRUSH_RULE_CHOOSELEAF_INDEP = 7,
59 
60 	CRUSH_RULE_SET_CHOOSE_TRIES = 8, /* override choose_total_tries */
61 	CRUSH_RULE_SET_CHOOSELEAF_TRIES = 9, /* override chooseleaf_descend_once */
62 	CRUSH_RULE_SET_CHOOSE_LOCAL_TRIES = 10,
63 	CRUSH_RULE_SET_CHOOSE_LOCAL_FALLBACK_TRIES = 11,
64 	CRUSH_RULE_SET_CHOOSELEAF_VARY_R = 12,
65 	CRUSH_RULE_SET_CHOOSELEAF_STABLE = 13
66 };
67 
68 /*
69  * for specifying choose num (arg1) relative to the max parameter
70  * passed to do_rule
71  */
72 #define CRUSH_CHOOSE_N            0
73 #define CRUSH_CHOOSE_N_MINUS(x)   (-(x))
74 
75 /*
76  * The rule mask is used to describe what the rule is intended for.
77  * Given a ruleset and size of output set, we search through the
78  * rule list for a matching rule_mask.
79  */
80 struct crush_rule_mask {
81 	__u8 ruleset;
82 	__u8 type;
83 	__u8 min_size;
84 	__u8 max_size;
85 };
86 
87 struct crush_rule {
88 	__u32 len;
89 	struct crush_rule_mask mask;
90 	struct crush_rule_step steps[];
91 };
92 
93 #define crush_rule_size(len) (sizeof(struct crush_rule) + \
94 			      (len)*sizeof(struct crush_rule_step))
95 
96 
97 
98 /*
99  * A bucket is a named container of other items (either devices or
100  * other buckets).  Items within a bucket are chosen using one of a
101  * few different algorithms.  The table summarizes how the speed of
102  * each option measures up against mapping stability when items are
103  * added or removed.
104  *
105  *  Bucket Alg     Speed       Additions    Removals
106  *  ------------------------------------------------
107  *  uniform         O(1)       poor         poor
108  *  list            O(n)       optimal      poor
109  *  tree            O(log n)   good         good
110  *  straw           O(n)       better       better
111  *  straw2          O(n)       optimal      optimal
112  */
113 enum {
114 	CRUSH_BUCKET_UNIFORM = 1,
115 	CRUSH_BUCKET_LIST = 2,
116 	CRUSH_BUCKET_TREE = 3,
117 	CRUSH_BUCKET_STRAW = 4,
118 	CRUSH_BUCKET_STRAW2 = 5,
119 };
120 extern const char *crush_bucket_alg_name(int alg);
121 
122 /*
123  * although tree was a legacy algorithm, it has been buggy, so
124  * exclude it.
125  */
126 #define CRUSH_LEGACY_ALLOWED_BUCKET_ALGS (	\
127 		(1 << CRUSH_BUCKET_UNIFORM) |	\
128 		(1 << CRUSH_BUCKET_LIST) |	\
129 		(1 << CRUSH_BUCKET_STRAW))
130 
131 struct crush_bucket {
132 	__s32 id;        /* this'll be negative */
133 	__u16 type;      /* non-zero; type=0 is reserved for devices */
134 	__u8 alg;        /* one of CRUSH_BUCKET_* */
135 	__u8 hash;       /* which hash function to use, CRUSH_HASH_* */
136 	__u32 weight;    /* 16-bit fixed point */
137 	__u32 size;      /* num items */
138 	__s32 *items;
139 
140 };
141 
142 /** @ingroup API
143  *
144  * Replacement weights for each item in a bucket. The size of the
145  * array must be exactly the size of the straw2 bucket, just as the
146  * item_weights array.
147  *
148  */
149 struct crush_weight_set {
150 	__u32 *weights; /*!< 16.16 fixed point weights
151                              in the same order as items */
152 	__u32 size;     /*!< size of the __weights__ array */
153 };
154 
155 /** @ingroup API
156  *
157  * Replacement weights and ids for a given straw2 bucket, for
158  * placement purposes.
159  *
160  * When crush_do_rule() chooses the Nth item from a straw2 bucket, the
161  * replacement weights found at __weight_set[N]__ are used instead of
162  * the weights from __item_weights__. If __N__ is greater than
163  * __weight_set_size__, the weights found at __weight_set_size-1__ are
164  * used instead. For instance if __weight_set__ is:
165  *
166  *    [ [ 0x10000, 0x20000 ],   // position 0
167  *      [ 0x20000, 0x40000 ] ]  // position 1
168  *
169  * choosing the 0th item will use position 0 weights [ 0x10000, 0x20000 ]
170  * choosing the 1th item will use position 1 weights [ 0x20000, 0x40000 ]
171  * choosing the 2th item will use position 1 weights [ 0x20000, 0x40000 ]
172  * etc.
173  *
174  */
175 struct crush_choose_arg {
176 	__s32 *ids;            /*!< values to use instead of items */
177 	__u32 ids_size;        /*!< size of the __ids__ array */
178 	struct crush_weight_set *weight_set; /*!< weight replacements for
179                                                   a given position */
180 	__u32 weight_set_size; /*!< size of the __weight_set__ array */
181 };
182 
183 /** @ingroup API
184  *
185  * Replacement weights and ids for each bucket in the crushmap. The
186  * __size__ of the __args__ array must be exactly the same as the
187  * __map->max_buckets__.
188  *
189  * The __crush_choose_arg__ at index N will be used when choosing
190  * an item from the bucket __map->buckets[N]__ bucket, provided it
191  * is a straw2 bucket.
192  *
193  */
194 struct crush_choose_arg_map {
195 #ifdef __KERNEL__
196 	struct rb_node node;
197 	s64 choose_args_index;
198 #endif
199 	struct crush_choose_arg *args; /*!< replacement for each bucket
200                                             in the crushmap */
201 	__u32 size;                    /*!< size of the __args__ array */
202 };
203 
204 struct crush_bucket_uniform {
205 	struct crush_bucket h;
206 	__u32 item_weight;  /* 16-bit fixed point; all items equally weighted */
207 };
208 
209 struct crush_bucket_list {
210 	struct crush_bucket h;
211 	__u32 *item_weights;  /* 16-bit fixed point */
212 	__u32 *sum_weights;   /* 16-bit fixed point.  element i is sum
213 				 of weights 0..i, inclusive */
214 };
215 
216 struct crush_bucket_tree {
217 	struct crush_bucket h;  /* note: h.size is _tree_ size, not number of
218 				   actual items */
219 	__u8 num_nodes;
220 	__u32 *node_weights;
221 };
222 
223 struct crush_bucket_straw {
224 	struct crush_bucket h;
225 	__u32 *item_weights;   /* 16-bit fixed point */
226 	__u32 *straws;         /* 16-bit fixed point */
227 };
228 
229 struct crush_bucket_straw2 {
230 	struct crush_bucket h;
231 	__u32 *item_weights;   /* 16-bit fixed point */
232 };
233 
234 
235 
236 /*
237  * CRUSH map includes all buckets, rules, etc.
238  */
239 struct crush_map {
240 	struct crush_bucket **buckets;
241 	struct crush_rule **rules;
242 
243 	__s32 max_buckets;
244 	__u32 max_rules;
245 	__s32 max_devices;
246 
247 	/* choose local retries before re-descent */
248 	__u32 choose_local_tries;
249 	/* choose local attempts using a fallback permutation before
250 	 * re-descent */
251 	__u32 choose_local_fallback_tries;
252 	/* choose attempts before giving up */
253 	__u32 choose_total_tries;
254 	/* attempt chooseleaf inner descent once for firstn mode; on
255 	 * reject retry outer descent.  Note that this does *not*
256 	 * apply to a collision: in that case we will retry as we used
257 	 * to. */
258 	__u32 chooseleaf_descend_once;
259 
260 	/* if non-zero, feed r into chooseleaf, bit-shifted right by (r-1)
261 	 * bits.  a value of 1 is best for new clusters.  for legacy clusters
262 	 * that want to limit reshuffling, a value of 3 or 4 will make the
263 	 * mappings line up a bit better with previous mappings. */
264 	__u8 chooseleaf_vary_r;
265 
266 	/* if true, it makes chooseleaf firstn to return stable results (if
267 	 * no local retry) so that data migrations would be optimal when some
268 	 * device fails. */
269 	__u8 chooseleaf_stable;
270 
271 	/*
272 	 * This value is calculated after decode or construction by
273 	 * the builder. It is exposed here (rather than having a
274 	 * 'build CRUSH working space' function) so that callers can
275 	 * reserve a static buffer, allocate space on the stack, or
276 	 * otherwise avoid calling into the heap allocator if they
277 	 * want to. The size of the working space depends on the map,
278 	 * while the size of the scratch vector passed to the mapper
279 	 * depends on the size of the desired result set.
280 	 *
281 	 * Nothing stops the caller from allocating both in one swell
282 	 * foop and passing in two points, though.
283 	 */
284 	size_t working_size;
285 
286 #ifndef __KERNEL__
287 	/*
288 	 * version 0 (original) of straw_calc has various flaws.  version 1
289 	 * fixes a few of them.
290 	 */
291 	__u8 straw_calc_version;
292 
293 	/*
294 	 * allowed bucket algs is a bitmask, here the bit positions
295 	 * are CRUSH_BUCKET_*.  note that these are *bits* and
296 	 * CRUSH_BUCKET_* values are not, so we need to or together (1
297 	 * << CRUSH_BUCKET_WHATEVER).  The 0th bit is not used to
298 	 * minimize confusion (bucket type values start at 1).
299 	 */
300 	__u32 allowed_bucket_algs;
301 
302 	__u32 *choose_tries;
303 #else
304 	/* device/bucket type id -> type name (CrushWrapper::type_map) */
305 	struct rb_root type_names;
306 
307 	/* device/bucket id -> name (CrushWrapper::name_map) */
308 	struct rb_root names;
309 
310 	/* CrushWrapper::choose_args */
311 	struct rb_root choose_args;
312 #endif
313 };
314 
315 
316 /* crush.c */
317 extern int crush_get_bucket_item_weight(const struct crush_bucket *b, int pos);
318 extern void crush_destroy_bucket_uniform(struct crush_bucket_uniform *b);
319 extern void crush_destroy_bucket_list(struct crush_bucket_list *b);
320 extern void crush_destroy_bucket_tree(struct crush_bucket_tree *b);
321 extern void crush_destroy_bucket_straw(struct crush_bucket_straw *b);
322 extern void crush_destroy_bucket_straw2(struct crush_bucket_straw2 *b);
323 extern void crush_destroy_bucket(struct crush_bucket *b);
324 extern void crush_destroy_rule(struct crush_rule *r);
325 extern void crush_destroy(struct crush_map *map);
326 
crush_calc_tree_node(int i)327 static inline int crush_calc_tree_node(int i)
328 {
329 	return ((i+1) << 1)-1;
330 }
331 
332 /*
333  * These data structures are private to the CRUSH implementation. They
334  * are exposed in this header file because builder needs their
335  * definitions to calculate the total working size.
336  *
337  * Moving this out of the crush map allow us to treat the CRUSH map as
338  * immutable within the mapper and removes the requirement for a CRUSH
339  * map lock.
340  */
341 struct crush_work_bucket {
342 	__u32 perm_x; /* @x for which *perm is defined */
343 	__u32 perm_n; /* num elements of *perm that are permuted/defined */
344 	__u32 *perm;  /* Permutation of the bucket's items */
345 };
346 
347 struct crush_work {
348 	struct crush_work_bucket **work; /* Per-bucket working store */
349 #ifdef __KERNEL__
350 	struct list_head item;
351 #endif
352 };
353 
354 #ifdef __KERNEL__
355 /* osdmap.c */
356 void clear_crush_names(struct rb_root *root);
357 void clear_choose_args(struct crush_map *c);
358 #endif
359 
360 #endif
361