Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /* |
| 2 | * lib/prio_tree.c - priority search tree |
| 3 | * |
| 4 | * Copyright (C) 2004, Rajesh Venkatasubramanian <vrajesh@umich.edu> |
| 5 | * |
| 6 | * This file is released under the GPL v2. |
| 7 | * |
| 8 | * Based on the radix priority search tree proposed by Edward M. McCreight |
| 9 | * SIAM Journal of Computing, vol. 14, no.2, pages 257-276, May 1985 |
| 10 | * |
| 11 | * 02Feb2004 Initial version |
| 12 | */ |
| 13 | |
| 14 | #include <linux/init.h> |
| 15 | #include <linux/mm.h> |
| 16 | #include <linux/prio_tree.h> |
| 17 | |
| 18 | /* |
| 19 | * A clever mix of heap and radix trees forms a radix priority search tree (PST) |
| 20 | * which is useful for storing intervals, e.g, we can consider a vma as a closed |
| 21 | * interval of file pages [offset_begin, offset_end], and store all vmas that |
| 22 | * map a file in a PST. Then, using the PST, we can answer a stabbing query, |
| 23 | * i.e., selecting a set of stored intervals (vmas) that overlap with (map) a |
| 24 | * given input interval X (a set of consecutive file pages), in "O(log n + m)" |
| 25 | * time where 'log n' is the height of the PST, and 'm' is the number of stored |
| 26 | * intervals (vmas) that overlap (map) with the input interval X (the set of |
| 27 | * consecutive file pages). |
| 28 | * |
| 29 | * In our implementation, we store closed intervals of the form [radix_index, |
| 30 | * heap_index]. We assume that always radix_index <= heap_index. McCreight's PST |
| 31 | * is designed for storing intervals with unique radix indices, i.e., each |
| 32 | * interval have different radix_index. However, this limitation can be easily |
| 33 | * overcome by using the size, i.e., heap_index - radix_index, as part of the |
| 34 | * index, so we index the tree using [(radix_index,size), heap_index]. |
| 35 | * |
| 36 | * When the above-mentioned indexing scheme is used, theoretically, in a 32 bit |
| 37 | * machine, the maximum height of a PST can be 64. We can use a balanced version |
| 38 | * of the priority search tree to optimize the tree height, but the balanced |
| 39 | * tree proposed by McCreight is too complex and memory-hungry for our purpose. |
| 40 | */ |
| 41 | |
| 42 | /* |
| 43 | * The following macros are used for implementing prio_tree for i_mmap |
| 44 | */ |
| 45 | |
| 46 | #define RADIX_INDEX(vma) ((vma)->vm_pgoff) |
| 47 | #define VMA_SIZE(vma) (((vma)->vm_end - (vma)->vm_start) >> PAGE_SHIFT) |
| 48 | /* avoid overflow */ |
| 49 | #define HEAP_INDEX(vma) ((vma)->vm_pgoff + (VMA_SIZE(vma) - 1)) |
| 50 | |
| 51 | |
| 52 | static void get_index(const struct prio_tree_root *root, |
| 53 | const struct prio_tree_node *node, |
| 54 | unsigned long *radix, unsigned long *heap) |
| 55 | { |
| 56 | if (root->raw) { |
| 57 | struct vm_area_struct *vma = prio_tree_entry( |
| 58 | node, struct vm_area_struct, shared.prio_tree_node); |
| 59 | |
| 60 | *radix = RADIX_INDEX(vma); |
| 61 | *heap = HEAP_INDEX(vma); |
| 62 | } |
| 63 | else { |
| 64 | *radix = node->start; |
| 65 | *heap = node->last; |
| 66 | } |
| 67 | } |
| 68 | |
| 69 | static unsigned long index_bits_to_maxindex[BITS_PER_LONG]; |
| 70 | |
| 71 | void __init prio_tree_init(void) |
| 72 | { |
| 73 | unsigned int i; |
| 74 | |
| 75 | for (i = 0; i < ARRAY_SIZE(index_bits_to_maxindex) - 1; i++) |
| 76 | index_bits_to_maxindex[i] = (1UL << (i + 1)) - 1; |
| 77 | index_bits_to_maxindex[ARRAY_SIZE(index_bits_to_maxindex) - 1] = ~0UL; |
| 78 | } |
| 79 | |
| 80 | /* |
| 81 | * Maximum heap_index that can be stored in a PST with index_bits bits |
| 82 | */ |
| 83 | static inline unsigned long prio_tree_maxindex(unsigned int bits) |
| 84 | { |
| 85 | return index_bits_to_maxindex[bits - 1]; |
| 86 | } |
| 87 | |
Xiao Guangrong | 97e834c | 2012-03-23 15:02:15 -0700 | [diff] [blame^] | 88 | static void prio_set_parent(struct prio_tree_node *parent, |
| 89 | struct prio_tree_node *child, bool left) |
| 90 | { |
| 91 | if (left) |
| 92 | parent->left = child; |
| 93 | else |
| 94 | parent->right = child; |
| 95 | |
| 96 | child->parent = parent; |
| 97 | } |
| 98 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 99 | /* |
| 100 | * Extend a priority search tree so that it can store a node with heap_index |
| 101 | * max_heap_index. In the worst case, this algorithm takes O((log n)^2). |
| 102 | * However, this function is used rarely and the common case performance is |
| 103 | * not bad. |
| 104 | */ |
| 105 | static struct prio_tree_node *prio_tree_expand(struct prio_tree_root *root, |
| 106 | struct prio_tree_node *node, unsigned long max_heap_index) |
| 107 | { |
Xiao Guangrong | 742245d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 108 | struct prio_tree_node *prev; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 109 | |
| 110 | if (max_heap_index > prio_tree_maxindex(root->index_bits)) |
| 111 | root->index_bits++; |
| 112 | |
Xiao Guangrong | 742245d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 113 | prev = node; |
| 114 | INIT_PRIO_TREE_NODE(node); |
| 115 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 116 | while (max_heap_index > prio_tree_maxindex(root->index_bits)) { |
Xiao Guangrong | 742245d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 117 | struct prio_tree_node *tmp = root->prio_tree_node; |
| 118 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 119 | root->index_bits++; |
| 120 | |
| 121 | if (prio_tree_empty(root)) |
| 122 | continue; |
| 123 | |
Xiao Guangrong | 742245d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 124 | prio_tree_remove(root, root->prio_tree_node); |
| 125 | INIT_PRIO_TREE_NODE(tmp); |
| 126 | |
Xiao Guangrong | 97e834c | 2012-03-23 15:02:15 -0700 | [diff] [blame^] | 127 | prio_set_parent(prev, tmp, true); |
Xiao Guangrong | 742245d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 128 | prev = tmp; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 129 | } |
| 130 | |
Xiao Guangrong | 97e834c | 2012-03-23 15:02:15 -0700 | [diff] [blame^] | 131 | if (!prio_tree_empty(root)) |
| 132 | prio_set_parent(prev, root->prio_tree_node, true); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 133 | |
| 134 | root->prio_tree_node = node; |
| 135 | return node; |
| 136 | } |
| 137 | |
| 138 | /* |
| 139 | * Replace a prio_tree_node with a new node and return the old node |
| 140 | */ |
| 141 | struct prio_tree_node *prio_tree_replace(struct prio_tree_root *root, |
| 142 | struct prio_tree_node *old, struct prio_tree_node *node) |
| 143 | { |
| 144 | INIT_PRIO_TREE_NODE(node); |
| 145 | |
| 146 | if (prio_tree_root(old)) { |
| 147 | BUG_ON(root->prio_tree_node != old); |
| 148 | /* |
| 149 | * We can reduce root->index_bits here. However, it is complex |
| 150 | * and does not help much to improve performance (IMO). |
| 151 | */ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 152 | root->prio_tree_node = node; |
Xiao Guangrong | 97e834c | 2012-03-23 15:02:15 -0700 | [diff] [blame^] | 153 | } else |
| 154 | prio_set_parent(old->parent, node, old->parent->left == old); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 155 | |
Xiao Guangrong | 97e834c | 2012-03-23 15:02:15 -0700 | [diff] [blame^] | 156 | if (!prio_tree_left_empty(old)) |
| 157 | prio_set_parent(node, old->left, true); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 158 | |
Xiao Guangrong | 97e834c | 2012-03-23 15:02:15 -0700 | [diff] [blame^] | 159 | if (!prio_tree_right_empty(old)) |
| 160 | prio_set_parent(node, old->right, false); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 161 | |
| 162 | return old; |
| 163 | } |
| 164 | |
| 165 | /* |
| 166 | * Insert a prio_tree_node @node into a radix priority search tree @root. The |
| 167 | * algorithm typically takes O(log n) time where 'log n' is the number of bits |
| 168 | * required to represent the maximum heap_index. In the worst case, the algo |
| 169 | * can take O((log n)^2) - check prio_tree_expand. |
| 170 | * |
| 171 | * If a prior node with same radix_index and heap_index is already found in |
| 172 | * the tree, then returns the address of the prior node. Otherwise, inserts |
| 173 | * @node into the tree and returns @node. |
| 174 | */ |
| 175 | struct prio_tree_node *prio_tree_insert(struct prio_tree_root *root, |
| 176 | struct prio_tree_node *node) |
| 177 | { |
| 178 | struct prio_tree_node *cur, *res = node; |
| 179 | unsigned long radix_index, heap_index; |
| 180 | unsigned long r_index, h_index, index, mask; |
| 181 | int size_flag = 0; |
| 182 | |
| 183 | get_index(root, node, &radix_index, &heap_index); |
| 184 | |
| 185 | if (prio_tree_empty(root) || |
| 186 | heap_index > prio_tree_maxindex(root->index_bits)) |
| 187 | return prio_tree_expand(root, node, heap_index); |
| 188 | |
| 189 | cur = root->prio_tree_node; |
| 190 | mask = 1UL << (root->index_bits - 1); |
| 191 | |
| 192 | while (mask) { |
| 193 | get_index(root, cur, &r_index, &h_index); |
| 194 | |
| 195 | if (r_index == radix_index && h_index == heap_index) |
| 196 | return cur; |
| 197 | |
| 198 | if (h_index < heap_index || |
| 199 | (h_index == heap_index && r_index > radix_index)) { |
| 200 | struct prio_tree_node *tmp = node; |
| 201 | node = prio_tree_replace(root, cur, node); |
| 202 | cur = tmp; |
| 203 | /* swap indices */ |
| 204 | index = r_index; |
| 205 | r_index = radix_index; |
| 206 | radix_index = index; |
| 207 | index = h_index; |
| 208 | h_index = heap_index; |
| 209 | heap_index = index; |
| 210 | } |
| 211 | |
| 212 | if (size_flag) |
| 213 | index = heap_index - radix_index; |
| 214 | else |
| 215 | index = radix_index; |
| 216 | |
| 217 | if (index & mask) { |
| 218 | if (prio_tree_right_empty(cur)) { |
| 219 | INIT_PRIO_TREE_NODE(node); |
Xiao Guangrong | 97e834c | 2012-03-23 15:02:15 -0700 | [diff] [blame^] | 220 | prio_set_parent(cur, node, false); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 221 | return res; |
| 222 | } else |
| 223 | cur = cur->right; |
| 224 | } else { |
| 225 | if (prio_tree_left_empty(cur)) { |
| 226 | INIT_PRIO_TREE_NODE(node); |
Xiao Guangrong | 97e834c | 2012-03-23 15:02:15 -0700 | [diff] [blame^] | 227 | prio_set_parent(cur, node, true); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 228 | return res; |
| 229 | } else |
| 230 | cur = cur->left; |
| 231 | } |
| 232 | |
| 233 | mask >>= 1; |
| 234 | |
| 235 | if (!mask) { |
| 236 | mask = 1UL << (BITS_PER_LONG - 1); |
| 237 | size_flag = 1; |
| 238 | } |
| 239 | } |
| 240 | /* Should not reach here */ |
| 241 | BUG(); |
| 242 | return NULL; |
| 243 | } |
| 244 | |
| 245 | /* |
| 246 | * Remove a prio_tree_node @node from a radix priority search tree @root. The |
| 247 | * algorithm takes O(log n) time where 'log n' is the number of bits required |
| 248 | * to represent the maximum heap_index. |
| 249 | */ |
| 250 | void prio_tree_remove(struct prio_tree_root *root, struct prio_tree_node *node) |
| 251 | { |
| 252 | struct prio_tree_node *cur; |
| 253 | unsigned long r_index, h_index_right, h_index_left; |
| 254 | |
| 255 | cur = node; |
| 256 | |
| 257 | while (!prio_tree_left_empty(cur) || !prio_tree_right_empty(cur)) { |
| 258 | if (!prio_tree_left_empty(cur)) |
| 259 | get_index(root, cur->left, &r_index, &h_index_left); |
| 260 | else { |
| 261 | cur = cur->right; |
| 262 | continue; |
| 263 | } |
| 264 | |
| 265 | if (!prio_tree_right_empty(cur)) |
| 266 | get_index(root, cur->right, &r_index, &h_index_right); |
| 267 | else { |
| 268 | cur = cur->left; |
| 269 | continue; |
| 270 | } |
| 271 | |
| 272 | /* both h_index_left and h_index_right cannot be 0 */ |
| 273 | if (h_index_left >= h_index_right) |
| 274 | cur = cur->left; |
| 275 | else |
| 276 | cur = cur->right; |
| 277 | } |
| 278 | |
| 279 | if (prio_tree_root(cur)) { |
| 280 | BUG_ON(root->prio_tree_node != cur); |
| 281 | __INIT_PRIO_TREE_ROOT(root, root->raw); |
| 282 | return; |
| 283 | } |
| 284 | |
| 285 | if (cur->parent->right == cur) |
| 286 | cur->parent->right = cur->parent; |
| 287 | else |
| 288 | cur->parent->left = cur->parent; |
| 289 | |
| 290 | while (cur != node) |
| 291 | cur = prio_tree_replace(root, cur->parent, cur); |
| 292 | } |
| 293 | |
Xiao Guangrong | f35368d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 294 | static void iter_walk_down(struct prio_tree_iter *iter) |
| 295 | { |
| 296 | iter->mask >>= 1; |
| 297 | if (iter->mask) { |
| 298 | if (iter->size_level) |
| 299 | iter->size_level++; |
| 300 | return; |
| 301 | } |
| 302 | |
| 303 | if (iter->size_level) { |
| 304 | BUG_ON(!prio_tree_left_empty(iter->cur)); |
| 305 | BUG_ON(!prio_tree_right_empty(iter->cur)); |
| 306 | iter->size_level++; |
| 307 | iter->mask = ULONG_MAX; |
| 308 | } else { |
| 309 | iter->size_level = 1; |
| 310 | iter->mask = 1UL << (BITS_PER_LONG - 1); |
| 311 | } |
| 312 | } |
| 313 | |
| 314 | static void iter_walk_up(struct prio_tree_iter *iter) |
| 315 | { |
| 316 | if (iter->mask == ULONG_MAX) |
| 317 | iter->mask = 1UL; |
| 318 | else if (iter->size_level == 1) |
| 319 | iter->mask = 1UL; |
| 320 | else |
| 321 | iter->mask <<= 1; |
| 322 | if (iter->size_level) |
| 323 | iter->size_level--; |
| 324 | if (!iter->size_level && (iter->value & iter->mask)) |
| 325 | iter->value ^= iter->mask; |
| 326 | } |
| 327 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 328 | /* |
| 329 | * Following functions help to enumerate all prio_tree_nodes in the tree that |
| 330 | * overlap with the input interval X [radix_index, heap_index]. The enumeration |
| 331 | * takes O(log n + m) time where 'log n' is the height of the tree (which is |
| 332 | * proportional to # of bits required to represent the maximum heap_index) and |
| 333 | * 'm' is the number of prio_tree_nodes that overlap the interval X. |
| 334 | */ |
| 335 | |
| 336 | static struct prio_tree_node *prio_tree_left(struct prio_tree_iter *iter, |
| 337 | unsigned long *r_index, unsigned long *h_index) |
| 338 | { |
| 339 | if (prio_tree_left_empty(iter->cur)) |
| 340 | return NULL; |
| 341 | |
| 342 | get_index(iter->root, iter->cur->left, r_index, h_index); |
| 343 | |
| 344 | if (iter->r_index <= *h_index) { |
| 345 | iter->cur = iter->cur->left; |
Xiao Guangrong | f35368d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 346 | iter_walk_down(iter); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 347 | return iter->cur; |
| 348 | } |
| 349 | |
| 350 | return NULL; |
| 351 | } |
| 352 | |
| 353 | static struct prio_tree_node *prio_tree_right(struct prio_tree_iter *iter, |
| 354 | unsigned long *r_index, unsigned long *h_index) |
| 355 | { |
| 356 | unsigned long value; |
| 357 | |
| 358 | if (prio_tree_right_empty(iter->cur)) |
| 359 | return NULL; |
| 360 | |
| 361 | if (iter->size_level) |
| 362 | value = iter->value; |
| 363 | else |
| 364 | value = iter->value | iter->mask; |
| 365 | |
| 366 | if (iter->h_index < value) |
| 367 | return NULL; |
| 368 | |
| 369 | get_index(iter->root, iter->cur->right, r_index, h_index); |
| 370 | |
| 371 | if (iter->r_index <= *h_index) { |
| 372 | iter->cur = iter->cur->right; |
Xiao Guangrong | f35368d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 373 | iter_walk_down(iter); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 374 | return iter->cur; |
| 375 | } |
| 376 | |
| 377 | return NULL; |
| 378 | } |
| 379 | |
| 380 | static struct prio_tree_node *prio_tree_parent(struct prio_tree_iter *iter) |
| 381 | { |
| 382 | iter->cur = iter->cur->parent; |
Xiao Guangrong | f35368d | 2012-03-23 15:02:15 -0700 | [diff] [blame] | 383 | iter_walk_up(iter); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 384 | return iter->cur; |
| 385 | } |
| 386 | |
| 387 | static inline int overlap(struct prio_tree_iter *iter, |
| 388 | unsigned long r_index, unsigned long h_index) |
| 389 | { |
| 390 | return iter->h_index >= r_index && iter->r_index <= h_index; |
| 391 | } |
| 392 | |
| 393 | /* |
| 394 | * prio_tree_first: |
| 395 | * |
| 396 | * Get the first prio_tree_node that overlaps with the interval [radix_index, |
| 397 | * heap_index]. Note that always radix_index <= heap_index. We do a pre-order |
| 398 | * traversal of the tree. |
| 399 | */ |
| 400 | static struct prio_tree_node *prio_tree_first(struct prio_tree_iter *iter) |
| 401 | { |
| 402 | struct prio_tree_root *root; |
| 403 | unsigned long r_index, h_index; |
| 404 | |
| 405 | INIT_PRIO_TREE_ITER(iter); |
| 406 | |
| 407 | root = iter->root; |
| 408 | if (prio_tree_empty(root)) |
| 409 | return NULL; |
| 410 | |
| 411 | get_index(root, root->prio_tree_node, &r_index, &h_index); |
| 412 | |
| 413 | if (iter->r_index > h_index) |
| 414 | return NULL; |
| 415 | |
| 416 | iter->mask = 1UL << (root->index_bits - 1); |
| 417 | iter->cur = root->prio_tree_node; |
| 418 | |
| 419 | while (1) { |
| 420 | if (overlap(iter, r_index, h_index)) |
| 421 | return iter->cur; |
| 422 | |
| 423 | if (prio_tree_left(iter, &r_index, &h_index)) |
| 424 | continue; |
| 425 | |
| 426 | if (prio_tree_right(iter, &r_index, &h_index)) |
| 427 | continue; |
| 428 | |
| 429 | break; |
| 430 | } |
| 431 | return NULL; |
| 432 | } |
| 433 | |
| 434 | /* |
| 435 | * prio_tree_next: |
| 436 | * |
| 437 | * Get the next prio_tree_node that overlaps with the input interval in iter |
| 438 | */ |
| 439 | struct prio_tree_node *prio_tree_next(struct prio_tree_iter *iter) |
| 440 | { |
| 441 | unsigned long r_index, h_index; |
| 442 | |
| 443 | if (iter->cur == NULL) |
| 444 | return prio_tree_first(iter); |
| 445 | |
| 446 | repeat: |
| 447 | while (prio_tree_left(iter, &r_index, &h_index)) |
| 448 | if (overlap(iter, r_index, h_index)) |
| 449 | return iter->cur; |
| 450 | |
| 451 | while (!prio_tree_right(iter, &r_index, &h_index)) { |
| 452 | while (!prio_tree_root(iter->cur) && |
| 453 | iter->cur->parent->right == iter->cur) |
| 454 | prio_tree_parent(iter); |
| 455 | |
| 456 | if (prio_tree_root(iter->cur)) |
| 457 | return NULL; |
| 458 | |
| 459 | prio_tree_parent(iter); |
| 460 | } |
| 461 | |
| 462 | if (overlap(iter, r_index, h_index)) |
| 463 | return iter->cur; |
| 464 | |
| 465 | goto repeat; |
| 466 | } |