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 * excercise 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 memset(node, 0, NODESIZE); 99 return node; 100 } 101 102 static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n) 103 { 104 size_t i; 105 106 for (i = 0; i < n; i++) { 107 if (l1[i] < l2[i]) 108 return -1; 109 if (l1[i] > l2[i]) 110 return 1; 111 } 112 return 0; 113 } 114 115 static unsigned long *longcpy(unsigned long *dest, const unsigned long *src, 116 size_t n) 117 { 118 size_t i; 119 120 for (i = 0; i < n; i++) 121 dest[i] = src[i]; 122 return dest; 123 } 124 125 static unsigned long *longset(unsigned long *s, unsigned long c, size_t n) 126 { 127 size_t i; 128 129 for (i = 0; i < n; i++) 130 s[i] = c; 131 return s; 132 } 133 134 static void dec_key(struct btree_geo *geo, unsigned long *key) 135 { 136 unsigned long val; 137 int i; 138 139 for (i = geo->keylen - 1; i >= 0; i--) { 140 val = key[i]; 141 key[i] = val - 1; 142 if (val) 143 break; 144 } 145 } 146 147 static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n) 148 { 149 return &node[n * geo->keylen]; 150 } 151 152 static void *bval(struct btree_geo *geo, unsigned long *node, int n) 153 { 154 return (void *)node[geo->no_longs + n]; 155 } 156 157 static void setkey(struct btree_geo *geo, unsigned long *node, int n, 158 unsigned long *key) 159 { 160 longcpy(bkey(geo, node, n), key, geo->keylen); 161 } 162 163 static void setval(struct btree_geo *geo, unsigned long *node, int n, 164 void *val) 165 { 166 node[geo->no_longs + n] = (unsigned long) val; 167 } 168 169 static void clearpair(struct btree_geo *geo, unsigned long *node, int n) 170 { 171 longset(bkey(geo, node, n), 0, geo->keylen); 172 node[geo->no_longs + n] = 0; 173 } 174 175 static inline void __btree_init(struct btree_head *head) 176 { 177 head->node = NULL; 178 head->height = 0; 179 } 180 181 void btree_init_mempool(struct btree_head *head, mempool_t *mempool) 182 { 183 __btree_init(head); 184 head->mempool = mempool; 185 } 186 EXPORT_SYMBOL_GPL(btree_init_mempool); 187 188 int btree_init(struct btree_head *head) 189 { 190 __btree_init(head); 191 head->mempool = mempool_create(0, btree_alloc, btree_free, NULL); 192 if (!head->mempool) 193 return -ENOMEM; 194 return 0; 195 } 196 EXPORT_SYMBOL_GPL(btree_init); 197 198 void btree_destroy(struct btree_head *head) 199 { 200 mempool_destroy(head->mempool); 201 head->mempool = NULL; 202 } 203 EXPORT_SYMBOL_GPL(btree_destroy); 204 205 void *btree_last(struct btree_head *head, struct btree_geo *geo, 206 unsigned long *key) 207 { 208 int height = head->height; 209 unsigned long *node = head->node; 210 211 if (height == 0) 212 return NULL; 213 214 for ( ; height > 1; height--) 215 node = bval(geo, node, 0); 216 217 longcpy(key, bkey(geo, node, 0), geo->keylen); 218 return bval(geo, node, 0); 219 } 220 EXPORT_SYMBOL_GPL(btree_last); 221 222 static int keycmp(struct btree_geo *geo, unsigned long *node, int pos, 223 unsigned long *key) 224 { 225 return longcmp(bkey(geo, node, pos), key, geo->keylen); 226 } 227 228 static int keyzero(struct btree_geo *geo, unsigned long *key) 229 { 230 int i; 231 232 for (i = 0; i < geo->keylen; i++) 233 if (key[i]) 234 return 0; 235 236 return 1; 237 } 238 239 void *btree_lookup(struct btree_head *head, struct btree_geo *geo, 240 unsigned long *key) 241 { 242 int i, height = head->height; 243 unsigned long *node = head->node; 244 245 if (height == 0) 246 return NULL; 247 248 for ( ; height > 1; height--) { 249 for (i = 0; i < geo->no_pairs; i++) 250 if (keycmp(geo, node, i, key) <= 0) 251 break; 252 if (i == geo->no_pairs) 253 return NULL; 254 node = bval(geo, node, i); 255 if (!node) 256 return NULL; 257 } 258 259 if (!node) 260 return NULL; 261 262 for (i = 0; i < geo->no_pairs; i++) 263 if (keycmp(geo, node, i, key) == 0) 264 return bval(geo, node, i); 265 return NULL; 266 } 267 EXPORT_SYMBOL_GPL(btree_lookup); 268 269 int btree_update(struct btree_head *head, struct btree_geo *geo, 270 unsigned long *key, void *val) 271 { 272 int i, height = head->height; 273 unsigned long *node = head->node; 274 275 if (height == 0) 276 return -ENOENT; 277 278 for ( ; height > 1; height--) { 279 for (i = 0; i < geo->no_pairs; i++) 280 if (keycmp(geo, node, i, key) <= 0) 281 break; 282 if (i == geo->no_pairs) 283 return -ENOENT; 284 node = bval(geo, node, i); 285 if (!node) 286 return -ENOENT; 287 } 288 289 if (!node) 290 return -ENOENT; 291 292 for (i = 0; i < geo->no_pairs; i++) 293 if (keycmp(geo, node, i, key) == 0) { 294 setval(geo, node, i, val); 295 return 0; 296 } 297 return -ENOENT; 298 } 299 EXPORT_SYMBOL_GPL(btree_update); 300 301 /* 302 * Usually this function is quite similar to normal lookup. But the key of 303 * a parent node may be smaller than the smallest key of all its siblings. 304 * In such a case we cannot just return NULL, as we have only proven that no 305 * key smaller than __key, but larger than this parent key exists. 306 * So we set __key to the parent key and retry. We have to use the smallest 307 * such parent key, which is the last parent key we encountered. 308 */ 309 void *btree_get_prev(struct btree_head *head, struct btree_geo *geo, 310 unsigned long *__key) 311 { 312 int i, height; 313 unsigned long *node, *oldnode; 314 unsigned long *retry_key = NULL, key[geo->keylen]; 315 316 if (keyzero(geo, __key)) 317 return NULL; 318 319 if (head->height == 0) 320 return NULL; 321 retry: 322 longcpy(key, __key, geo->keylen); 323 dec_key(geo, key); 324 325 node = head->node; 326 for (height = head->height ; height > 1; height--) { 327 for (i = 0; i < geo->no_pairs; i++) 328 if (keycmp(geo, node, i, key) <= 0) 329 break; 330 if (i == geo->no_pairs) 331 goto miss; 332 oldnode = node; 333 node = bval(geo, node, i); 334 if (!node) 335 goto miss; 336 retry_key = bkey(geo, oldnode, i); 337 } 338 339 if (!node) 340 goto miss; 341 342 for (i = 0; i < geo->no_pairs; i++) { 343 if (keycmp(geo, node, i, key) <= 0) { 344 if (bval(geo, node, i)) { 345 longcpy(__key, bkey(geo, node, i), geo->keylen); 346 return bval(geo, node, i); 347 } else 348 goto miss; 349 } 350 } 351 miss: 352 if (retry_key) { 353 __key = retry_key; 354 retry_key = NULL; 355 goto retry; 356 } 357 return NULL; 358 } 359 360 static int getpos(struct btree_geo *geo, unsigned long *node, 361 unsigned long *key) 362 { 363 int i; 364 365 for (i = 0; i < geo->no_pairs; i++) { 366 if (keycmp(geo, node, i, key) <= 0) 367 break; 368 } 369 return i; 370 } 371 372 static int getfill(struct btree_geo *geo, unsigned long *node, int start) 373 { 374 int i; 375 376 for (i = start; i < geo->no_pairs; i++) 377 if (!bval(geo, node, i)) 378 break; 379 return i; 380 } 381 382 /* 383 * locate the correct leaf node in the btree 384 */ 385 static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo, 386 unsigned long *key, int level) 387 { 388 unsigned long *node = head->node; 389 int i, height; 390 391 for (height = head->height; height > level; height--) { 392 for (i = 0; i < geo->no_pairs; i++) 393 if (keycmp(geo, node, i, key) <= 0) 394 break; 395 396 if ((i == geo->no_pairs) || !bval(geo, node, i)) { 397 /* right-most key is too large, update it */ 398 /* FIXME: If the right-most key on higher levels is 399 * always zero, this wouldn't be necessary. */ 400 i--; 401 setkey(geo, node, i, key); 402 } 403 BUG_ON(i < 0); 404 node = bval(geo, node, i); 405 } 406 BUG_ON(!node); 407 return node; 408 } 409 410 static int btree_grow(struct btree_head *head, struct btree_geo *geo, 411 gfp_t gfp) 412 { 413 unsigned long *node; 414 int fill; 415 416 node = btree_node_alloc(head, gfp); 417 if (!node) 418 return -ENOMEM; 419 if (head->node) { 420 fill = getfill(geo, head->node, 0); 421 setkey(geo, node, 0, bkey(geo, head->node, fill - 1)); 422 setval(geo, node, 0, head->node); 423 } 424 head->node = node; 425 head->height++; 426 return 0; 427 } 428 429 static void btree_shrink(struct btree_head *head, struct btree_geo *geo) 430 { 431 unsigned long *node; 432 int fill; 433 434 if (head->height <= 1) 435 return; 436 437 node = head->node; 438 fill = getfill(geo, node, 0); 439 BUG_ON(fill > 1); 440 head->node = bval(geo, node, 0); 441 head->height--; 442 mempool_free(node, head->mempool); 443 } 444 445 static int btree_insert_level(struct btree_head *head, struct btree_geo *geo, 446 unsigned long *key, void *val, int level, 447 gfp_t gfp) 448 { 449 unsigned long *node; 450 int i, pos, fill, err; 451 452 BUG_ON(!val); 453 if (head->height < level) { 454 err = btree_grow(head, geo, gfp); 455 if (err) 456 return err; 457 } 458 459 retry: 460 node = find_level(head, geo, key, level); 461 pos = getpos(geo, node, key); 462 fill = getfill(geo, node, pos); 463 /* two identical keys are not allowed */ 464 BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0); 465 466 if (fill == geo->no_pairs) { 467 /* need to split node */ 468 unsigned long *new; 469 470 new = btree_node_alloc(head, gfp); 471 if (!new) 472 return -ENOMEM; 473 err = btree_insert_level(head, geo, 474 bkey(geo, node, fill / 2 - 1), 475 new, level + 1, gfp); 476 if (err) { 477 mempool_free(new, head->mempool); 478 return err; 479 } 480 for (i = 0; i < fill / 2; i++) { 481 setkey(geo, new, i, bkey(geo, node, i)); 482 setval(geo, new, i, bval(geo, node, i)); 483 setkey(geo, node, i, bkey(geo, node, i + fill / 2)); 484 setval(geo, node, i, bval(geo, node, i + fill / 2)); 485 clearpair(geo, node, i + fill / 2); 486 } 487 if (fill & 1) { 488 setkey(geo, node, i, bkey(geo, node, fill - 1)); 489 setval(geo, node, i, bval(geo, node, fill - 1)); 490 clearpair(geo, node, fill - 1); 491 } 492 goto retry; 493 } 494 BUG_ON(fill >= geo->no_pairs); 495 496 /* shift and insert */ 497 for (i = fill; i > pos; i--) { 498 setkey(geo, node, i, bkey(geo, node, i - 1)); 499 setval(geo, node, i, bval(geo, node, i - 1)); 500 } 501 setkey(geo, node, pos, key); 502 setval(geo, node, pos, val); 503 504 return 0; 505 } 506 507 int btree_insert(struct btree_head *head, struct btree_geo *geo, 508 unsigned long *key, void *val, gfp_t gfp) 509 { 510 return btree_insert_level(head, geo, key, val, 1, gfp); 511 } 512 EXPORT_SYMBOL_GPL(btree_insert); 513 514 static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo, 515 unsigned long *key, int level); 516 static void merge(struct btree_head *head, struct btree_geo *geo, int level, 517 unsigned long *left, int lfill, 518 unsigned long *right, int rfill, 519 unsigned long *parent, int lpos) 520 { 521 int i; 522 523 for (i = 0; i < rfill; i++) { 524 /* Move all keys to the left */ 525 setkey(geo, left, lfill + i, bkey(geo, right, i)); 526 setval(geo, left, lfill + i, bval(geo, right, i)); 527 } 528 /* Exchange left and right child in parent */ 529 setval(geo, parent, lpos, right); 530 setval(geo, parent, lpos + 1, left); 531 /* Remove left (formerly right) child from parent */ 532 btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1); 533 mempool_free(right, head->mempool); 534 } 535 536 static void rebalance(struct btree_head *head, struct btree_geo *geo, 537 unsigned long *key, int level, unsigned long *child, int fill) 538 { 539 unsigned long *parent, *left = NULL, *right = NULL; 540 int i, no_left, no_right; 541 542 if (fill == 0) { 543 /* Because we don't steal entries from a neigbour, this case 544 * can happen. Parent node contains a single child, this 545 * node, so merging with a sibling never happens. 546 */ 547 btree_remove_level(head, geo, key, level + 1); 548 mempool_free(child, head->mempool); 549 return; 550 } 551 552 parent = find_level(head, geo, key, level + 1); 553 i = getpos(geo, parent, key); 554 BUG_ON(bval(geo, parent, i) != child); 555 556 if (i > 0) { 557 left = bval(geo, parent, i - 1); 558 no_left = getfill(geo, left, 0); 559 if (fill + no_left <= geo->no_pairs) { 560 merge(head, geo, level, 561 left, no_left, 562 child, fill, 563 parent, i - 1); 564 return; 565 } 566 } 567 if (i + 1 < getfill(geo, parent, i)) { 568 right = bval(geo, parent, i + 1); 569 no_right = getfill(geo, right, 0); 570 if (fill + no_right <= geo->no_pairs) { 571 merge(head, geo, level, 572 child, fill, 573 right, no_right, 574 parent, i); 575 return; 576 } 577 } 578 /* 579 * We could also try to steal one entry from the left or right 580 * neighbor. By not doing so we changed the invariant from 581 * "all nodes are at least half full" to "no two neighboring 582 * nodes can be merged". Which means that the average fill of 583 * all nodes is still half or better. 584 */ 585 } 586 587 static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo, 588 unsigned long *key, int level) 589 { 590 unsigned long *node; 591 int i, pos, fill; 592 void *ret; 593 594 if (level > head->height) { 595 /* we recursed all the way up */ 596 head->height = 0; 597 head->node = NULL; 598 return NULL; 599 } 600 601 node = find_level(head, geo, key, level); 602 pos = getpos(geo, node, key); 603 fill = getfill(geo, node, pos); 604 if ((level == 1) && (keycmp(geo, node, pos, key) != 0)) 605 return NULL; 606 ret = bval(geo, node, pos); 607 608 /* remove and shift */ 609 for (i = pos; i < fill - 1; i++) { 610 setkey(geo, node, i, bkey(geo, node, i + 1)); 611 setval(geo, node, i, bval(geo, node, i + 1)); 612 } 613 clearpair(geo, node, fill - 1); 614 615 if (fill - 1 < geo->no_pairs / 2) { 616 if (level < head->height) 617 rebalance(head, geo, key, level, node, fill - 1); 618 else if (fill - 1 == 1) 619 btree_shrink(head, geo); 620 } 621 622 return ret; 623 } 624 625 void *btree_remove(struct btree_head *head, struct btree_geo *geo, 626 unsigned long *key) 627 { 628 if (head->height == 0) 629 return NULL; 630 631 return btree_remove_level(head, geo, key, 1); 632 } 633 EXPORT_SYMBOL_GPL(btree_remove); 634 635 int btree_merge(struct btree_head *target, struct btree_head *victim, 636 struct btree_geo *geo, gfp_t gfp) 637 { 638 unsigned long key[geo->keylen]; 639 unsigned long dup[geo->keylen]; 640 void *val; 641 int err; 642 643 BUG_ON(target == victim); 644 645 if (!(target->node)) { 646 /* target is empty, just copy fields over */ 647 target->node = victim->node; 648 target->height = victim->height; 649 __btree_init(victim); 650 return 0; 651 } 652 653 /* TODO: This needs some optimizations. Currently we do three tree 654 * walks to remove a single object from the victim. 655 */ 656 for (;;) { 657 if (!btree_last(victim, geo, key)) 658 break; 659 val = btree_lookup(victim, geo, key); 660 err = btree_insert(target, geo, key, val, gfp); 661 if (err) 662 return err; 663 /* We must make a copy of the key, as the original will get 664 * mangled inside btree_remove. */ 665 longcpy(dup, key, geo->keylen); 666 btree_remove(victim, geo, dup); 667 } 668 return 0; 669 } 670 EXPORT_SYMBOL_GPL(btree_merge); 671 672 static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo, 673 unsigned long *node, unsigned long opaque, 674 void (*func)(void *elem, unsigned long opaque, 675 unsigned long *key, size_t index, 676 void *func2), 677 void *func2, int reap, int height, size_t count) 678 { 679 int i; 680 unsigned long *child; 681 682 for (i = 0; i < geo->no_pairs; i++) { 683 child = bval(geo, node, i); 684 if (!child) 685 break; 686 if (height > 1) 687 count = __btree_for_each(head, geo, child, opaque, 688 func, func2, reap, height - 1, count); 689 else 690 func(child, opaque, bkey(geo, node, i), count++, 691 func2); 692 } 693 if (reap) 694 mempool_free(node, head->mempool); 695 return count; 696 } 697 698 static void empty(void *elem, unsigned long opaque, unsigned long *key, 699 size_t index, void *func2) 700 { 701 } 702 703 void visitorl(void *elem, unsigned long opaque, unsigned long *key, 704 size_t index, void *__func) 705 { 706 visitorl_t func = __func; 707 708 func(elem, opaque, *key, index); 709 } 710 EXPORT_SYMBOL_GPL(visitorl); 711 712 void visitor32(void *elem, unsigned long opaque, unsigned long *__key, 713 size_t index, void *__func) 714 { 715 visitor32_t func = __func; 716 u32 *key = (void *)__key; 717 718 func(elem, opaque, *key, index); 719 } 720 EXPORT_SYMBOL_GPL(visitor32); 721 722 void visitor64(void *elem, unsigned long opaque, unsigned long *__key, 723 size_t index, void *__func) 724 { 725 visitor64_t func = __func; 726 u64 *key = (void *)__key; 727 728 func(elem, opaque, *key, index); 729 } 730 EXPORT_SYMBOL_GPL(visitor64); 731 732 void visitor128(void *elem, unsigned long opaque, unsigned long *__key, 733 size_t index, void *__func) 734 { 735 visitor128_t func = __func; 736 u64 *key = (void *)__key; 737 738 func(elem, opaque, key[0], key[1], index); 739 } 740 EXPORT_SYMBOL_GPL(visitor128); 741 742 size_t btree_visitor(struct btree_head *head, struct btree_geo *geo, 743 unsigned long opaque, 744 void (*func)(void *elem, unsigned long opaque, 745 unsigned long *key, 746 size_t index, void *func2), 747 void *func2) 748 { 749 size_t count = 0; 750 751 if (!func2) 752 func = empty; 753 if (head->node) 754 count = __btree_for_each(head, geo, head->node, opaque, func, 755 func2, 0, head->height, 0); 756 return count; 757 } 758 EXPORT_SYMBOL_GPL(btree_visitor); 759 760 size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo, 761 unsigned long opaque, 762 void (*func)(void *elem, unsigned long opaque, 763 unsigned long *key, 764 size_t index, void *func2), 765 void *func2) 766 { 767 size_t count = 0; 768 769 if (!func2) 770 func = empty; 771 if (head->node) 772 count = __btree_for_each(head, geo, head->node, opaque, func, 773 func2, 1, head->height, 0); 774 __btree_init(head); 775 return count; 776 } 777 EXPORT_SYMBOL_GPL(btree_grim_visitor); 778 779 static int __init btree_module_init(void) 780 { 781 btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0, 782 SLAB_HWCACHE_ALIGN, NULL); 783 return 0; 784 } 785 786 static void __exit btree_module_exit(void) 787 { 788 kmem_cache_destroy(btree_cachep); 789 } 790 791 /* If core code starts using btree, initialization should happen even earlier */ 792 module_init(btree_module_init); 793 module_exit(btree_module_exit); 794 795 MODULE_AUTHOR("Joern Engel <joern@logfs.org>"); 796 MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>"); 797 MODULE_LICENSE("GPL"); 798