1 /* 2 * lib/btree.c - Simple In-memory B+Tree 3 * 4 * As should be obvious for Linux kernel code, license is GPLv2 5 * 6 * Copyright (c) 2007-2008 Joern Engel <joern@logfs.org> 7 * Bits and pieces stolen from Peter Zijlstra's code, which is 8 * Copyright 2007, Red Hat Inc. Peter Zijlstra <pzijlstr@redhat.com> 9 * GPLv2 10 * 11 * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch 12 * 13 * A relatively simple B+Tree implementation. I have written it as a learning 14 * exercise to understand how B+Trees work. Turned out to be useful as well. 15 * 16 * B+Trees can be used similar to Linux radix trees (which don't have anything 17 * in common with textbook radix trees, beware). Prerequisite for them working 18 * well is that access to a random tree node is much faster than a large number 19 * of operations within each node. 20 * 21 * Disks have fulfilled the prerequisite for a long time. More recently DRAM 22 * has gained similar properties, as memory access times, when measured in cpu 23 * cycles, have increased. Cacheline sizes have increased as well, which also 24 * helps B+Trees. 25 * 26 * Compared to radix trees, B+Trees are more efficient when dealing with a 27 * sparsely populated address space. Between 25% and 50% of the memory is 28 * occupied with valid pointers. When densely populated, radix trees contain 29 * ~98% pointers - hard to beat. Very sparse radix trees contain only ~2% 30 * pointers. 31 * 32 * This particular implementation stores pointers identified by a long value. 33 * Storing NULL pointers is illegal, lookup will return NULL when no entry 34 * was found. 35 * 36 * A tricks was used that is not commonly found in textbooks. The lowest 37 * values are to the right, not to the left. All used slots within a node 38 * are on the left, all unused slots contain NUL values. Most operations 39 * simply loop once over all slots and terminate on the first NUL. 40 */ 41 42 #include <linux/btree.h> 43 #include <linux/cache.h> 44 #include <linux/kernel.h> 45 #include <linux/slab.h> 46 #include <linux/module.h> 47 48 #define MAX(a, b) ((a) > (b) ? (a) : (b)) 49 #define NODESIZE MAX(L1_CACHE_BYTES, 128) 50 51 struct btree_geo { 52 int keylen; 53 int no_pairs; 54 int no_longs; 55 }; 56 57 struct btree_geo btree_geo32 = { 58 .keylen = 1, 59 .no_pairs = NODESIZE / sizeof(long) / 2, 60 .no_longs = NODESIZE / sizeof(long) / 2, 61 }; 62 EXPORT_SYMBOL_GPL(btree_geo32); 63 64 #define LONG_PER_U64 (64 / BITS_PER_LONG) 65 struct btree_geo btree_geo64 = { 66 .keylen = LONG_PER_U64, 67 .no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64), 68 .no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)), 69 }; 70 EXPORT_SYMBOL_GPL(btree_geo64); 71 72 struct btree_geo btree_geo128 = { 73 .keylen = 2 * LONG_PER_U64, 74 .no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64), 75 .no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)), 76 }; 77 EXPORT_SYMBOL_GPL(btree_geo128); 78 79 static struct kmem_cache *btree_cachep; 80 81 void *btree_alloc(gfp_t gfp_mask, void *pool_data) 82 { 83 return kmem_cache_alloc(btree_cachep, gfp_mask); 84 } 85 EXPORT_SYMBOL_GPL(btree_alloc); 86 87 void btree_free(void *element, void *pool_data) 88 { 89 kmem_cache_free(btree_cachep, element); 90 } 91 EXPORT_SYMBOL_GPL(btree_free); 92 93 static unsigned long *btree_node_alloc(struct btree_head *head, gfp_t gfp) 94 { 95 unsigned long *node; 96 97 node = mempool_alloc(head->mempool, gfp); 98 if (likely(node)) 99 memset(node, 0, NODESIZE); 100 return node; 101 } 102 103 static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n) 104 { 105 size_t i; 106 107 for (i = 0; i < n; i++) { 108 if (l1[i] < l2[i]) 109 return -1; 110 if (l1[i] > l2[i]) 111 return 1; 112 } 113 return 0; 114 } 115 116 static unsigned long *longcpy(unsigned long *dest, const unsigned long *src, 117 size_t n) 118 { 119 size_t i; 120 121 for (i = 0; i < n; i++) 122 dest[i] = src[i]; 123 return dest; 124 } 125 126 static unsigned long *longset(unsigned long *s, unsigned long c, size_t n) 127 { 128 size_t i; 129 130 for (i = 0; i < n; i++) 131 s[i] = c; 132 return s; 133 } 134 135 static void dec_key(struct btree_geo *geo, unsigned long *key) 136 { 137 unsigned long val; 138 int i; 139 140 for (i = geo->keylen - 1; i >= 0; i--) { 141 val = key[i]; 142 key[i] = val - 1; 143 if (val) 144 break; 145 } 146 } 147 148 static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n) 149 { 150 return &node[n * geo->keylen]; 151 } 152 153 static void *bval(struct btree_geo *geo, unsigned long *node, int n) 154 { 155 return (void *)node[geo->no_longs + n]; 156 } 157 158 static void setkey(struct btree_geo *geo, unsigned long *node, int n, 159 unsigned long *key) 160 { 161 longcpy(bkey(geo, node, n), key, geo->keylen); 162 } 163 164 static void setval(struct btree_geo *geo, unsigned long *node, int n, 165 void *val) 166 { 167 node[geo->no_longs + n] = (unsigned long) val; 168 } 169 170 static void clearpair(struct btree_geo *geo, unsigned long *node, int n) 171 { 172 longset(bkey(geo, node, n), 0, geo->keylen); 173 node[geo->no_longs + n] = 0; 174 } 175 176 static inline void __btree_init(struct btree_head *head) 177 { 178 head->node = NULL; 179 head->height = 0; 180 } 181 182 void btree_init_mempool(struct btree_head *head, mempool_t *mempool) 183 { 184 __btree_init(head); 185 head->mempool = mempool; 186 } 187 EXPORT_SYMBOL_GPL(btree_init_mempool); 188 189 int btree_init(struct btree_head *head) 190 { 191 __btree_init(head); 192 head->mempool = mempool_create(0, btree_alloc, btree_free, NULL); 193 if (!head->mempool) 194 return -ENOMEM; 195 return 0; 196 } 197 EXPORT_SYMBOL_GPL(btree_init); 198 199 void btree_destroy(struct btree_head *head) 200 { 201 mempool_destroy(head->mempool); 202 head->mempool = NULL; 203 } 204 EXPORT_SYMBOL_GPL(btree_destroy); 205 206 void *btree_last(struct btree_head *head, struct btree_geo *geo, 207 unsigned long *key) 208 { 209 int height = head->height; 210 unsigned long *node = head->node; 211 212 if (height == 0) 213 return NULL; 214 215 for ( ; height > 1; height--) 216 node = bval(geo, node, 0); 217 218 longcpy(key, bkey(geo, node, 0), geo->keylen); 219 return bval(geo, node, 0); 220 } 221 EXPORT_SYMBOL_GPL(btree_last); 222 223 static int keycmp(struct btree_geo *geo, unsigned long *node, int pos, 224 unsigned long *key) 225 { 226 return longcmp(bkey(geo, node, pos), key, geo->keylen); 227 } 228 229 static int keyzero(struct btree_geo *geo, unsigned long *key) 230 { 231 int i; 232 233 for (i = 0; i < geo->keylen; i++) 234 if (key[i]) 235 return 0; 236 237 return 1; 238 } 239 240 void *btree_lookup(struct btree_head *head, struct btree_geo *geo, 241 unsigned long *key) 242 { 243 int i, height = head->height; 244 unsigned long *node = head->node; 245 246 if (height == 0) 247 return NULL; 248 249 for ( ; height > 1; height--) { 250 for (i = 0; i < geo->no_pairs; i++) 251 if (keycmp(geo, node, i, key) <= 0) 252 break; 253 if (i == geo->no_pairs) 254 return NULL; 255 node = bval(geo, node, i); 256 if (!node) 257 return NULL; 258 } 259 260 if (!node) 261 return NULL; 262 263 for (i = 0; i < geo->no_pairs; i++) 264 if (keycmp(geo, node, i, key) == 0) 265 return bval(geo, node, i); 266 return NULL; 267 } 268 EXPORT_SYMBOL_GPL(btree_lookup); 269 270 int btree_update(struct btree_head *head, struct btree_geo *geo, 271 unsigned long *key, void *val) 272 { 273 int i, height = head->height; 274 unsigned long *node = head->node; 275 276 if (height == 0) 277 return -ENOENT; 278 279 for ( ; height > 1; height--) { 280 for (i = 0; i < geo->no_pairs; i++) 281 if (keycmp(geo, node, i, key) <= 0) 282 break; 283 if (i == geo->no_pairs) 284 return -ENOENT; 285 node = bval(geo, node, i); 286 if (!node) 287 return -ENOENT; 288 } 289 290 if (!node) 291 return -ENOENT; 292 293 for (i = 0; i < geo->no_pairs; i++) 294 if (keycmp(geo, node, i, key) == 0) { 295 setval(geo, node, i, val); 296 return 0; 297 } 298 return -ENOENT; 299 } 300 EXPORT_SYMBOL_GPL(btree_update); 301 302 /* 303 * Usually this function is quite similar to normal lookup. But the key of 304 * a parent node may be smaller than the smallest key of all its siblings. 305 * In such a case we cannot just return NULL, as we have only proven that no 306 * key smaller than __key, but larger than this parent key exists. 307 * So we set __key to the parent key and retry. We have to use the smallest 308 * such parent key, which is the last parent key we encountered. 309 */ 310 void *btree_get_prev(struct btree_head *head, struct btree_geo *geo, 311 unsigned long *__key) 312 { 313 int i, height; 314 unsigned long *node, *oldnode; 315 unsigned long *retry_key = NULL, key[geo->keylen]; 316 317 if (keyzero(geo, __key)) 318 return NULL; 319 320 if (head->height == 0) 321 return NULL; 322 longcpy(key, __key, geo->keylen); 323 retry: 324 dec_key(geo, key); 325 326 node = head->node; 327 for (height = head->height ; height > 1; height--) { 328 for (i = 0; i < geo->no_pairs; i++) 329 if (keycmp(geo, node, i, key) <= 0) 330 break; 331 if (i == geo->no_pairs) 332 goto miss; 333 oldnode = node; 334 node = bval(geo, node, i); 335 if (!node) 336 goto miss; 337 retry_key = bkey(geo, oldnode, i); 338 } 339 340 if (!node) 341 goto miss; 342 343 for (i = 0; i < geo->no_pairs; i++) { 344 if (keycmp(geo, node, i, key) <= 0) { 345 if (bval(geo, node, i)) { 346 longcpy(__key, bkey(geo, node, i), geo->keylen); 347 return bval(geo, node, i); 348 } else 349 goto miss; 350 } 351 } 352 miss: 353 if (retry_key) { 354 longcpy(key, retry_key, geo->keylen); 355 retry_key = NULL; 356 goto retry; 357 } 358 return NULL; 359 } 360 EXPORT_SYMBOL_GPL(btree_get_prev); 361 362 static int getpos(struct btree_geo *geo, unsigned long *node, 363 unsigned long *key) 364 { 365 int i; 366 367 for (i = 0; i < geo->no_pairs; i++) { 368 if (keycmp(geo, node, i, key) <= 0) 369 break; 370 } 371 return i; 372 } 373 374 static int getfill(struct btree_geo *geo, unsigned long *node, int start) 375 { 376 int i; 377 378 for (i = start; i < geo->no_pairs; i++) 379 if (!bval(geo, node, i)) 380 break; 381 return i; 382 } 383 384 /* 385 * locate the correct leaf node in the btree 386 */ 387 static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo, 388 unsigned long *key, int level) 389 { 390 unsigned long *node = head->node; 391 int i, height; 392 393 for (height = head->height; height > level; height--) { 394 for (i = 0; i < geo->no_pairs; i++) 395 if (keycmp(geo, node, i, key) <= 0) 396 break; 397 398 if ((i == geo->no_pairs) || !bval(geo, node, i)) { 399 /* right-most key is too large, update it */ 400 /* FIXME: If the right-most key on higher levels is 401 * always zero, this wouldn't be necessary. */ 402 i--; 403 setkey(geo, node, i, key); 404 } 405 BUG_ON(i < 0); 406 node = bval(geo, node, i); 407 } 408 BUG_ON(!node); 409 return node; 410 } 411 412 static int btree_grow(struct btree_head *head, struct btree_geo *geo, 413 gfp_t gfp) 414 { 415 unsigned long *node; 416 int fill; 417 418 node = btree_node_alloc(head, gfp); 419 if (!node) 420 return -ENOMEM; 421 if (head->node) { 422 fill = getfill(geo, head->node, 0); 423 setkey(geo, node, 0, bkey(geo, head->node, fill - 1)); 424 setval(geo, node, 0, head->node); 425 } 426 head->node = node; 427 head->height++; 428 return 0; 429 } 430 431 static void btree_shrink(struct btree_head *head, struct btree_geo *geo) 432 { 433 unsigned long *node; 434 int fill; 435 436 if (head->height <= 1) 437 return; 438 439 node = head->node; 440 fill = getfill(geo, node, 0); 441 BUG_ON(fill > 1); 442 head->node = bval(geo, node, 0); 443 head->height--; 444 mempool_free(node, head->mempool); 445 } 446 447 static int btree_insert_level(struct btree_head *head, struct btree_geo *geo, 448 unsigned long *key, void *val, int level, 449 gfp_t gfp) 450 { 451 unsigned long *node; 452 int i, pos, fill, err; 453 454 BUG_ON(!val); 455 if (head->height < level) { 456 err = btree_grow(head, geo, gfp); 457 if (err) 458 return err; 459 } 460 461 retry: 462 node = find_level(head, geo, key, level); 463 pos = getpos(geo, node, key); 464 fill = getfill(geo, node, pos); 465 /* two identical keys are not allowed */ 466 BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0); 467 468 if (fill == geo->no_pairs) { 469 /* need to split node */ 470 unsigned long *new; 471 472 new = btree_node_alloc(head, gfp); 473 if (!new) 474 return -ENOMEM; 475 err = btree_insert_level(head, geo, 476 bkey(geo, node, fill / 2 - 1), 477 new, level + 1, gfp); 478 if (err) { 479 mempool_free(new, head->mempool); 480 return err; 481 } 482 for (i = 0; i < fill / 2; i++) { 483 setkey(geo, new, i, bkey(geo, node, i)); 484 setval(geo, new, i, bval(geo, node, i)); 485 setkey(geo, node, i, bkey(geo, node, i + fill / 2)); 486 setval(geo, node, i, bval(geo, node, i + fill / 2)); 487 clearpair(geo, node, i + fill / 2); 488 } 489 if (fill & 1) { 490 setkey(geo, node, i, bkey(geo, node, fill - 1)); 491 setval(geo, node, i, bval(geo, node, fill - 1)); 492 clearpair(geo, node, fill - 1); 493 } 494 goto retry; 495 } 496 BUG_ON(fill >= geo->no_pairs); 497 498 /* shift and insert */ 499 for (i = fill; i > pos; i--) { 500 setkey(geo, node, i, bkey(geo, node, i - 1)); 501 setval(geo, node, i, bval(geo, node, i - 1)); 502 } 503 setkey(geo, node, pos, key); 504 setval(geo, node, pos, val); 505 506 return 0; 507 } 508 509 int btree_insert(struct btree_head *head, struct btree_geo *geo, 510 unsigned long *key, void *val, gfp_t gfp) 511 { 512 BUG_ON(!val); 513 return btree_insert_level(head, geo, key, val, 1, gfp); 514 } 515 EXPORT_SYMBOL_GPL(btree_insert); 516 517 static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo, 518 unsigned long *key, int level); 519 static void merge(struct btree_head *head, struct btree_geo *geo, int level, 520 unsigned long *left, int lfill, 521 unsigned long *right, int rfill, 522 unsigned long *parent, int lpos) 523 { 524 int i; 525 526 for (i = 0; i < rfill; i++) { 527 /* Move all keys to the left */ 528 setkey(geo, left, lfill + i, bkey(geo, right, i)); 529 setval(geo, left, lfill + i, bval(geo, right, i)); 530 } 531 /* Exchange left and right child in parent */ 532 setval(geo, parent, lpos, right); 533 setval(geo, parent, lpos + 1, left); 534 /* Remove left (formerly right) child from parent */ 535 btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1); 536 mempool_free(right, head->mempool); 537 } 538 539 static void rebalance(struct btree_head *head, struct btree_geo *geo, 540 unsigned long *key, int level, unsigned long *child, int fill) 541 { 542 unsigned long *parent, *left = NULL, *right = NULL; 543 int i, no_left, no_right; 544 545 if (fill == 0) { 546 /* Because we don't steal entries from a neighbour, this case 547 * can happen. Parent node contains a single child, this 548 * node, so merging with a sibling never happens. 549 */ 550 btree_remove_level(head, geo, key, level + 1); 551 mempool_free(child, head->mempool); 552 return; 553 } 554 555 parent = find_level(head, geo, key, level + 1); 556 i = getpos(geo, parent, key); 557 BUG_ON(bval(geo, parent, i) != child); 558 559 if (i > 0) { 560 left = bval(geo, parent, i - 1); 561 no_left = getfill(geo, left, 0); 562 if (fill + no_left <= geo->no_pairs) { 563 merge(head, geo, level, 564 left, no_left, 565 child, fill, 566 parent, i - 1); 567 return; 568 } 569 } 570 if (i + 1 < getfill(geo, parent, i)) { 571 right = bval(geo, parent, i + 1); 572 no_right = getfill(geo, right, 0); 573 if (fill + no_right <= geo->no_pairs) { 574 merge(head, geo, level, 575 child, fill, 576 right, no_right, 577 parent, i); 578 return; 579 } 580 } 581 /* 582 * We could also try to steal one entry from the left or right 583 * neighbor. By not doing so we changed the invariant from 584 * "all nodes are at least half full" to "no two neighboring 585 * nodes can be merged". Which means that the average fill of 586 * all nodes is still half or better. 587 */ 588 } 589 590 static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo, 591 unsigned long *key, int level) 592 { 593 unsigned long *node; 594 int i, pos, fill; 595 void *ret; 596 597 if (level > head->height) { 598 /* we recursed all the way up */ 599 head->height = 0; 600 head->node = NULL; 601 return NULL; 602 } 603 604 node = find_level(head, geo, key, level); 605 pos = getpos(geo, node, key); 606 fill = getfill(geo, node, pos); 607 if ((level == 1) && (keycmp(geo, node, pos, key) != 0)) 608 return NULL; 609 ret = bval(geo, node, pos); 610 611 /* remove and shift */ 612 for (i = pos; i < fill - 1; i++) { 613 setkey(geo, node, i, bkey(geo, node, i + 1)); 614 setval(geo, node, i, bval(geo, node, i + 1)); 615 } 616 clearpair(geo, node, fill - 1); 617 618 if (fill - 1 < geo->no_pairs / 2) { 619 if (level < head->height) 620 rebalance(head, geo, key, level, node, fill - 1); 621 else if (fill - 1 == 1) 622 btree_shrink(head, geo); 623 } 624 625 return ret; 626 } 627 628 void *btree_remove(struct btree_head *head, struct btree_geo *geo, 629 unsigned long *key) 630 { 631 if (head->height == 0) 632 return NULL; 633 634 return btree_remove_level(head, geo, key, 1); 635 } 636 EXPORT_SYMBOL_GPL(btree_remove); 637 638 int btree_merge(struct btree_head *target, struct btree_head *victim, 639 struct btree_geo *geo, gfp_t gfp) 640 { 641 unsigned long key[geo->keylen]; 642 unsigned long dup[geo->keylen]; 643 void *val; 644 int err; 645 646 BUG_ON(target == victim); 647 648 if (!(target->node)) { 649 /* target is empty, just copy fields over */ 650 target->node = victim->node; 651 target->height = victim->height; 652 __btree_init(victim); 653 return 0; 654 } 655 656 /* TODO: This needs some optimizations. Currently we do three tree 657 * walks to remove a single object from the victim. 658 */ 659 for (;;) { 660 if (!btree_last(victim, geo, key)) 661 break; 662 val = btree_lookup(victim, geo, key); 663 err = btree_insert(target, geo, key, val, gfp); 664 if (err) 665 return err; 666 /* We must make a copy of the key, as the original will get 667 * mangled inside btree_remove. */ 668 longcpy(dup, key, geo->keylen); 669 btree_remove(victim, geo, dup); 670 } 671 return 0; 672 } 673 EXPORT_SYMBOL_GPL(btree_merge); 674 675 static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo, 676 unsigned long *node, unsigned long opaque, 677 void (*func)(void *elem, unsigned long opaque, 678 unsigned long *key, size_t index, 679 void *func2), 680 void *func2, int reap, int height, size_t count) 681 { 682 int i; 683 unsigned long *child; 684 685 for (i = 0; i < geo->no_pairs; i++) { 686 child = bval(geo, node, i); 687 if (!child) 688 break; 689 if (height > 1) 690 count = __btree_for_each(head, geo, child, opaque, 691 func, func2, reap, height - 1, count); 692 else 693 func(child, opaque, bkey(geo, node, i), count++, 694 func2); 695 } 696 if (reap) 697 mempool_free(node, head->mempool); 698 return count; 699 } 700 701 static void empty(void *elem, unsigned long opaque, unsigned long *key, 702 size_t index, void *func2) 703 { 704 } 705 706 void visitorl(void *elem, unsigned long opaque, unsigned long *key, 707 size_t index, void *__func) 708 { 709 visitorl_t func = __func; 710 711 func(elem, opaque, *key, index); 712 } 713 EXPORT_SYMBOL_GPL(visitorl); 714 715 void visitor32(void *elem, unsigned long opaque, unsigned long *__key, 716 size_t index, void *__func) 717 { 718 visitor32_t func = __func; 719 u32 *key = (void *)__key; 720 721 func(elem, opaque, *key, index); 722 } 723 EXPORT_SYMBOL_GPL(visitor32); 724 725 void visitor64(void *elem, unsigned long opaque, unsigned long *__key, 726 size_t index, void *__func) 727 { 728 visitor64_t func = __func; 729 u64 *key = (void *)__key; 730 731 func(elem, opaque, *key, index); 732 } 733 EXPORT_SYMBOL_GPL(visitor64); 734 735 void visitor128(void *elem, unsigned long opaque, unsigned long *__key, 736 size_t index, void *__func) 737 { 738 visitor128_t func = __func; 739 u64 *key = (void *)__key; 740 741 func(elem, opaque, key[0], key[1], index); 742 } 743 EXPORT_SYMBOL_GPL(visitor128); 744 745 size_t btree_visitor(struct btree_head *head, struct btree_geo *geo, 746 unsigned long opaque, 747 void (*func)(void *elem, unsigned long opaque, 748 unsigned long *key, 749 size_t index, void *func2), 750 void *func2) 751 { 752 size_t count = 0; 753 754 if (!func2) 755 func = empty; 756 if (head->node) 757 count = __btree_for_each(head, geo, head->node, opaque, func, 758 func2, 0, head->height, 0); 759 return count; 760 } 761 EXPORT_SYMBOL_GPL(btree_visitor); 762 763 size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo, 764 unsigned long opaque, 765 void (*func)(void *elem, unsigned long opaque, 766 unsigned long *key, 767 size_t index, void *func2), 768 void *func2) 769 { 770 size_t count = 0; 771 772 if (!func2) 773 func = empty; 774 if (head->node) 775 count = __btree_for_each(head, geo, head->node, opaque, func, 776 func2, 1, head->height, 0); 777 __btree_init(head); 778 return count; 779 } 780 EXPORT_SYMBOL_GPL(btree_grim_visitor); 781 782 static int __init btree_module_init(void) 783 { 784 btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0, 785 SLAB_HWCACHE_ALIGN, NULL); 786 return 0; 787 } 788 789 static void __exit btree_module_exit(void) 790 { 791 kmem_cache_destroy(btree_cachep); 792 } 793 794 /* If core code starts using btree, initialization should happen even earlier */ 795 module_init(btree_module_init); 796 module_exit(btree_module_exit); 797 798 MODULE_AUTHOR("Joern Engel <joern@logfs.org>"); 799 MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>"); 800 MODULE_LICENSE("GPL"); 801