lib/radix-tree.c

   1 /*
   2  * Copyright (C) 2001 Momchil Velikov
   3  * Portions Copyright (C) 2001 Christoph Hellwig
   4  * Copyright (C) 2005 SGI, Christoph Lameter <clameter@sgi.com>
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License as
   8  * published by the Free Software Foundation; either version 2, or (at
   9  * your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19  */
  20
  21 #include <linux/errno.h>
  22 #include <linux/init.h>
  23 #include <linux/kernel.h>
  24 #include <linux/module.h>
  25 #include <linux/radix-tree.h>
  26 #include <linux/percpu.h>
  27 #include <linux/slab.h>
  28 #include <linux/notifier.h>
  29 #include <linux/cpu.h>
  30 #include <linux/gfp.h>
  31 #include <linux/string.h>
  32 #include <linux/bitops.h>
  33
  34
  35 #ifdef __KERNEL__
  36 #define RADIX_TREE_MAP_SHIFT    6
  37 #else
  38 #define RADIX_TREE_MAP_SHIFT    3       /* For more stressful testing */
  39 #endif
  40 #define RADIX_TREE_TAGS         2
  41
  42 #define RADIX_TREE_MAP_SIZE     (1UL << RADIX_TREE_MAP_SHIFT)
  43 #define RADIX_TREE_MAP_MASK     (RADIX_TREE_MAP_SIZE-1)
  44
  45 #define RADIX_TREE_TAG_LONGS    \
  46         ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
  47
  48 struct radix_tree_node {
  49         unsigned int    count;
  50         void            *slots[RADIX_TREE_MAP_SIZE];
  51         unsigned long   tags[RADIX_TREE_TAGS][RADIX_TREE_TAG_LONGS];
  52 };
  53
  54 struct radix_tree_path {
  55         struct radix_tree_node *node;
  56         int offset;
  57 };
  58
  59 #define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
  60 #define RADIX_TREE_MAX_PATH (RADIX_TREE_INDEX_BITS/RADIX_TREE_MAP_SHIFT + 2)
  61
  62 static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH] __read_mostly;
  63
  64 /*
  65  * Radix tree node cache.
  66  */
  67 static kmem_cache_t *radix_tree_node_cachep;
  68
  69 /*
  70  * Per-cpu pool of preloaded nodes
  71  */
  72 struct radix_tree_preload {
  73         int nr;
  74         struct radix_tree_node *nodes[RADIX_TREE_MAX_PATH];
  75 };
  76 DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
  77
  78 /*
  79  * This assumes that the caller has performed appropriate preallocation, and
  80  * that the caller has pinned this thread of control to the current CPU.
  81  */
  82 static struct radix_tree_node *
  83 radix_tree_node_alloc(struct radix_tree_root *root)
  84 {
  85         struct radix_tree_node *ret;
  86
  87         ret = kmem_cache_alloc(radix_tree_node_cachep, root->gfp_mask);
  88         if (ret == NULL && !(root->gfp_mask & __GFP_WAIT)) {
  89                 struct radix_tree_preload *rtp;
  90
  91                 rtp = &__get_cpu_var(radix_tree_preloads);
  92                 if (rtp->nr) {
  93                         ret = rtp->nodes[rtp->nr - 1];
  94                         rtp->nodes[rtp->nr - 1] = NULL;
  95                         rtp->nr--;
  96                 }
  97         }
  98         return ret;
  99 }
 100
 101 static inline void
 102 radix_tree_node_free(struct radix_tree_node *node)
 103 {
 104         kmem_cache_free(radix_tree_node_cachep, node);
 105 }
 106
 107 /*
 108  * Load up this CPU's radix_tree_node buffer with sufficient objects to
 109  * ensure that the addition of a single element in the tree cannot fail.  On
 110  * success, return zero, with preemption disabled.  On error, return -ENOMEM
 111  * with preemption not disabled.
 112  */
 113 int radix_tree_preload(gfp_t gfp_mask)
 114 {
 115         struct radix_tree_preload *rtp;
 116         struct radix_tree_node *node;
 117         int ret = -ENOMEM;
 118
 119         preempt_disable();
 120         rtp = &__get_cpu_var(radix_tree_preloads);
 121         while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {
 122                 preempt_enable();
 123                 node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
 124                 if (node == NULL)
 125                         goto out;
 126                 preempt_disable();
 127                 rtp = &__get_cpu_var(radix_tree_preloads);
 128                 if (rtp->nr < ARRAY_SIZE(rtp->nodes))
 129                         rtp->nodes[rtp->nr++] = node;
 130                 else
 131                         kmem_cache_free(radix_tree_node_cachep, node);
 132         }
 133         ret = 0;
 134 out:
 135         return ret;
 136 }
 137
 138 static inline void tag_set(struct radix_tree_node *node, int tag, int offset)
 139 {
 140         __set_bit(offset, node->tags[tag]);
 141 }
 142
 143 static inline void tag_clear(struct radix_tree_node *node, int tag, int offset)
 144 {
 145         __clear_bit(offset, node->tags[tag]);
 146 }
 147
 148 static inline int tag_get(struct radix_tree_node *node, int tag, int offset)
 149 {
 150         return test_bit(offset, node->tags[tag]);
 151 }
 152
 153 /*
 154  * Returns 1 if any slot in the node has this tag set.
 155  * Otherwise returns 0.
 156  */
 157 static inline int any_tag_set(struct radix_tree_node *node, int tag)
 158 {
 159         int idx;
 160         for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
 161                 if (node->tags[tag][idx])
 162                         return 1;
 163         }
 164         return 0;
 165 }
 166
 167 /*
 168  *      Return the maximum key which can be store into a
 169  *      radix tree with height HEIGHT.
 170  */
 171 static inline unsigned long radix_tree_maxindex(unsigned int height)
 172 {
 173         return height_to_maxindex[height];
 174 }
 175
 176 /*
 177  *      Extend a radix tree so it can store key @index.
 178  */
 179 static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
 180 {
 181         struct radix_tree_node *node;
 182         unsigned int height;
 183         char tags[RADIX_TREE_TAGS];
 184         int tag;
 185
 186         /* Figure out what the height should be.  */
 187         height = root->height + 1;
 188         while (index > radix_tree_maxindex(height))
 189                 height++;
 190
 191         if (root->rnode == NULL) {
 192                 root->height = height;
 193                 goto out;
 194         }
 195
 196         /*
 197          * Prepare the tag status of the top-level node for propagation
 198          * into the newly-pushed top-level node(s)
 199          */
 200         for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
 201                 tags[tag] = 0;
 202                 if (any_tag_set(root->rnode, tag))
 203                         tags[tag] = 1;
 204         }
 205
 206         do {
 207                 if (!(node = radix_tree_node_alloc(root)))
 208                         return -ENOMEM;
 209
 210                 /* Increase the height.  */
 211                 node->slots[0] = root->rnode;
 212
 213                 /* Propagate the aggregated tag info into the new root */
 214                 for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
 215                         if (tags[tag])
 216                                 tag_set(node, tag, 0);
 217                 }
 218
 219                 node->count = 1;
 220                 root->rnode = node;
 221                 root->height++;
 222         } while (height > root->height);
 223 out:
 224         return 0;
 225 }
 226
 227 /**
 228  *      radix_tree_insert    -    insert into a radix tree
 229  *      @root:          radix tree root
 230  *      @index:         index key
 231  *      @item:          item to insert
 232  *
 233  *      Insert an item into the radix tree at position @index.
 234  */
 235 int radix_tree_insert(struct radix_tree_root *root,
 236                         unsigned long index, void *item)
 237 {
 238         struct radix_tree_node *node = NULL, *slot;
 239         unsigned int height, shift;
 240         int offset;
 241         int error;
 242
 243         /* Make sure the tree is high enough.  */
 244         if ((!index && !root->rnode) ||
 245                         index > radix_tree_maxindex(root->height)) {
 246                 error = radix_tree_extend(root, index);
 247                 if (error)
 248                         return error;
 249         }
 250
 251         slot = root->rnode;
 252         height = root->height;
 253         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 254
 255         offset = 0;                     /* uninitialised var warning */
 256         do {
 257                 if (slot == NULL) {
 258                         /* Have to add a child node.  */
 259                         if (!(slot = radix_tree_node_alloc(root)))
 260                                 return -ENOMEM;
 261                         if (node) {
 262                                 node->slots[offset] = slot;
 263                                 node->count++;
 264                         } else
 265                                 root->rnode = slot;
 266                 }
 267
 268                 /* Go a level down */
 269                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 270                 node = slot;
 271                 slot = node->slots[offset];
 272                 shift -= RADIX_TREE_MAP_SHIFT;
 273                 height--;
 274         } while (height > 0);
 275
 276         if (slot != NULL)
 277                 return -EEXIST;
 278
 279         BUG_ON(!node);
 280         node->count++;
 281         node->slots[offset] = item;
 282         BUG_ON(tag_get(node, 0, offset));
 283         BUG_ON(tag_get(node, 1, offset));
 284
 285         return 0;
 286 }
 287 EXPORT_SYMBOL(radix_tree_insert);
 288
 289 static inline void **__lookup_slot(struct radix_tree_root *root,
 290                                    unsigned long index)
 291 {
 292         unsigned int height, shift;
 293         struct radix_tree_node **slot;
 294
 295         height = root->height;
 296         if (index > radix_tree_maxindex(height))
 297                 return NULL;
 298
 299         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 300         slot = &root->rnode;
 301
 302         while (height > 0) {
 303                 if (*slot == NULL)
 304                         return NULL;
 305
 306                 slot = (struct radix_tree_node **)
 307                         ((*slot)->slots +
 308                                 ((index >> shift) & RADIX_TREE_MAP_MASK));
 309                 shift -= RADIX_TREE_MAP_SHIFT;
 310                 height--;
 311         }
 312
 313         return (void **)slot;
 314 }
 315
 316 /**
 317  *      radix_tree_lookup_slot    -    lookup a slot in a radix tree
 318  *      @root:          radix tree root
 319  *      @index:         index key
 320  *
 321  *      Lookup the slot corresponding to the position @index in the radix tree
 322  *      @root. This is useful for update-if-exists operations.
 323  */
 324 void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
 325 {
 326         return __lookup_slot(root, index);
 327 }
 328 EXPORT_SYMBOL(radix_tree_lookup_slot);
 329
 330 /**
 331  *      radix_tree_lookup    -    perform lookup operation on a radix tree
 332  *      @root:          radix tree root
 333  *      @index:         index key
 334  *
 335  *      Lookup the item at the position @index in the radix tree @root.
 336  */
 337 void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
 338 {
 339         void **slot;
 340
 341         slot = __lookup_slot(root, index);
 342         return slot != NULL ? *slot : NULL;
 343 }
 344 EXPORT_SYMBOL(radix_tree_lookup);
 345
 346 /**
 347  *      radix_tree_tag_set - set a tag on a radix tree node
 348  *      @root:          radix tree root
 349  *      @index:         index key
 350  *      @tag:           tag index
 351  *
 352  *      Set the search tag corresponging to @index in the radix tree.  From
 353  *      the root all the way down to the leaf node.
 354  *
 355  *      Returns the address of the tagged item.   Setting a tag on a not-present
 356  *      item is a bug.
 357  */
 358 void *radix_tree_tag_set(struct radix_tree_root *root,
 359                         unsigned long index, int tag)
 360 {
 361         unsigned int height, shift;
 362         struct radix_tree_node *slot;
 363
 364         height = root->height;
 365         if (index > radix_tree_maxindex(height))
 366                 return NULL;
 367
 368         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 369         slot = root->rnode;
 370
 371         while (height > 0) {
 372                 int offset;
 373
 374                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 375                 if (!tag_get(slot, tag, offset))
 376                         tag_set(slot, tag, offset);
 377                 slot = slot->slots[offset];
 378                 BUG_ON(slot == NULL);
 379                 shift -= RADIX_TREE_MAP_SHIFT;
 380                 height--;
 381         }
 382
 383         return slot;
 384 }
 385 EXPORT_SYMBOL(radix_tree_tag_set);
 386
 387 /**
 388  *      radix_tree_tag_clear - clear a tag on a radix tree node
 389  *      @root:          radix tree root
 390  *      @index:         index key
 391  *      @tag:           tag index
 392  *
 393  *      Clear the search tag corresponging to @index in the radix tree.  If
 394  *      this causes the leaf node to have no tags set then clear the tag in the
 395  *      next-to-leaf node, etc.
 396  *
 397  *      Returns the address of the tagged item on success, else NULL.  ie:
 398  *      has the same return value and semantics as radix_tree_lookup().
 399  */
 400 void *radix_tree_tag_clear(struct radix_tree_root *root,
 401                         unsigned long index, int tag)
 402 {
 403         struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
 404         struct radix_tree_node *slot;
 405         unsigned int height, shift;
 406         void *ret = NULL;
 407
 408         height = root->height;
 409         if (index > radix_tree_maxindex(height))
 410                 goto out;
 411
 412         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 413         pathp->node = NULL;
 414         slot = root->rnode;
 415
 416         while (height > 0) {
 417                 int offset;
 418
 419                 if (slot == NULL)
 420                         goto out;
 421
 422                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 423                 pathp[1].offset = offset;
 424                 pathp[1].node = slot;
 425                 slot = slot->slots[offset];
 426                 pathp++;
 427                 shift -= RADIX_TREE_MAP_SHIFT;
 428                 height--;
 429         }
 430
 431         ret = slot;
 432         if (ret == NULL)
 433                 goto out;
 434
 435         do {
 436                 if (!tag_get(pathp->node, tag, pathp->offset))
 437                         goto out;
 438                 tag_clear(pathp->node, tag, pathp->offset);
 439                 if (any_tag_set(pathp->node, tag))
 440                         goto out;
 441                 pathp--;
 442         } while (pathp->node);
 443 out:
 444         return ret;
 445 }
 446 EXPORT_SYMBOL(radix_tree_tag_clear);
 447
 448 #ifndef __KERNEL__      /* Only the test harness uses this at present */
 449 /**
 450  * radix_tree_tag_get - get a tag on a radix tree node
 451  * @root:               radix tree root
 452  * @index:              index key
 453  * @tag:                tag index
 454  *
 455  * Return values:
 456  *
 457  *  0: tag not present
 458  *  1: tag present, set
 459  * -1: tag present, unset
 460  */
 461 int radix_tree_tag_get(struct radix_tree_root *root,
 462                         unsigned long index, int tag)
 463 {
 464         unsigned int height, shift;
 465         struct radix_tree_node *slot;
 466         int saw_unset_tag = 0;
 467
 468         height = root->height;
 469         if (index > radix_tree_maxindex(height))
 470                 return 0;
 471
 472         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 473         slot = root->rnode;
 474
 475         for ( ; ; ) {
 476                 int offset;
 477
 478                 if (slot == NULL)
 479                         return 0;
 480
 481                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 482
 483                 /*
 484                  * This is just a debug check.  Later, we can bale as soon as
 485                  * we see an unset tag.
 486                  */
 487                 if (!tag_get(slot, tag, offset))
 488                         saw_unset_tag = 1;
 489                 if (height == 1) {
 490                         int ret = tag_get(slot, tag, offset);
 491
 492                         BUG_ON(ret && saw_unset_tag);
 493                         return ret ? 1 : -1;
 494                 }
 495                 slot = slot->slots[offset];
 496                 shift -= RADIX_TREE_MAP_SHIFT;
 497                 height--;
 498         }
 499 }
 500 EXPORT_SYMBOL(radix_tree_tag_get);
 501 #endif
 502
 503 static unsigned int
 504 __lookup(struct radix_tree_root *root, void **results, unsigned long index,
 505         unsigned int max_items, unsigned long *next_index)
 506 {
 507         unsigned int nr_found = 0;
 508         unsigned int shift, height;
 509         struct radix_tree_node *slot;
 510         unsigned long i;
 511
 512         height = root->height;
 513         if (height == 0)
 514                 goto out;
 515
 516         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 517         slot = root->rnode;
 518
 519         for ( ; height > 1; height--) {
 520
 521                 for (i = (index >> shift) & RADIX_TREE_MAP_MASK ;
 522                                 i < RADIX_TREE_MAP_SIZE; i++) {
 523                         if (slot->slots[i] != NULL)
 524                                 break;
 525                         index &= ~((1UL << shift) - 1);
 526                         index += 1UL << shift;
 527                         if (index == 0)
 528                                 goto out;       /* 32-bit wraparound */
 529                 }
 530                 if (i == RADIX_TREE_MAP_SIZE)
 531                         goto out;
 532
 533                 shift -= RADIX_TREE_MAP_SHIFT;
 534                 slot = slot->slots[i];
 535         }
 536
 537         /* Bottom level: grab some items */
 538         for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) {
 539                 index++;
 540                 if (slot->slots[i]) {
 541                         results[nr_found++] = slot->slots[i];
 542                         if (nr_found == max_items)
 543                                 goto out;
 544                 }
 545         }
 546 out:
 547         *next_index = index;
 548         return nr_found;
 549 }
 550
 551 /**
 552  *      radix_tree_gang_lookup - perform multiple lookup on a radix tree
 553  *      @root:          radix tree root
 554  *      @results:       where the results of the lookup are placed
 555  *      @first_index:   start the lookup from this key
 556  *      @max_items:     place up to this many items at *results
 557  *
 558  *      Performs an index-ascending scan of the tree for present items.  Places
 559  *      them at *@results and returns the number of items which were placed at
 560  *      *@results.
 561  *
 562  *      The implementation is naive.
 563  */
 564 unsigned int
 565 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 566                         unsigned long first_index, unsigned int max_items)
 567 {
 568         const unsigned long max_index = radix_tree_maxindex(root->height);
 569         unsigned long cur_index = first_index;
 570         unsigned int ret = 0;
 571
 572         while (ret < max_items) {
 573                 unsigned int nr_found;
 574                 unsigned long next_index;       /* Index of next search */
 575
 576                 if (cur_index > max_index)
 577                         break;
 578                 nr_found = __lookup(root, results + ret, cur_index,
 579                                         max_items - ret, &next_index);
 580                 ret += nr_found;
 581                 if (next_index == 0)
 582                         break;
 583                 cur_index = next_index;
 584         }
 585         return ret;
 586 }
 587 EXPORT_SYMBOL(radix_tree_gang_lookup);
 588
 589 /*
 590  * FIXME: the two tag_get()s here should use find_next_bit() instead of
 591  * open-coding the search.
 592  */
 593 static unsigned int
 594 __lookup_tag(struct radix_tree_root *root, void **results, unsigned long index,
 595         unsigned int max_items, unsigned long *next_index, int tag)
 596 {
 597         unsigned int nr_found = 0;
 598         unsigned int shift;
 599         unsigned int height = root->height;
 600         struct radix_tree_node *slot;
 601
 602         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 603         slot = root->rnode;
 604
 605         while (height > 0) {
 606                 unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;
 607
 608                 for ( ; i < RADIX_TREE_MAP_SIZE; i++) {
 609                         if (tag_get(slot, tag, i)) {
 610                                 BUG_ON(slot->slots[i] == NULL);
 611                                 break;
 612                         }
 613                         index &= ~((1UL << shift) - 1);
 614                         index += 1UL << shift;
 615                         if (index == 0)
 616                                 goto out;       /* 32-bit wraparound */
 617                 }
 618                 if (i == RADIX_TREE_MAP_SIZE)
 619                         goto out;
 620                 height--;
 621                 if (height == 0) {      /* Bottom level: grab some items */
 622                         unsigned long j = index & RADIX_TREE_MAP_MASK;
 623
 624                         for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
 625                                 index++;
 626                                 if (tag_get(slot, tag, j)) {
 627                                         BUG_ON(slot->slots[j] == NULL);
 628                                         results[nr_found++] = slot->slots[j];
 629                                         if (nr_found == max_items)
 630                                                 goto out;
 631                                 }
 632                         }
 633                 }
 634                 shift -= RADIX_TREE_MAP_SHIFT;
 635                 slot = slot->slots[i];
 636         }
 637 out:
 638         *next_index = index;
 639         return nr_found;
 640 }
 641
 642 /**
 643  *      radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
 644  *                                   based on a tag
 645  *      @root:          radix tree root
 646  *      @results:       where the results of the lookup are placed
 647  *      @first_index:   start the lookup from this key
 648  *      @max_items:     place up to this many items at *results
 649  *      @tag:           the tag index
 650  *
 651  *      Performs an index-ascending scan of the tree for present items which
 652  *      have the tag indexed by @tag set.  Places the items at *@results and
 653  *      returns the number of items which were placed at *@results.
 654  */
 655 unsigned int
 656 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 657                 unsigned long first_index, unsigned int max_items, int tag)
 658 {
 659         const unsigned long max_index = radix_tree_maxindex(root->height);
 660         unsigned long cur_index = first_index;
 661         unsigned int ret = 0;
 662
 663         while (ret < max_items) {
 664                 unsigned int nr_found;
 665                 unsigned long next_index;       /* Index of next search */
 666
 667                 if (cur_index > max_index)
 668                         break;
 669                 nr_found = __lookup_tag(root, results + ret, cur_index,
 670                                         max_items - ret, &next_index, tag);
 671                 ret += nr_found;
 672                 if (next_index == 0)
 673                         break;
 674                 cur_index = next_index;
 675         }
 676         return ret;
 677 }
 678 EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
 679
 680 /**
 681  *      radix_tree_shrink    -    shrink height of a radix tree to minimal
 682  *      @root           radix tree root
 683  */
 684 static inline void radix_tree_shrink(struct radix_tree_root *root)
 685 {
 686         /* try to shrink tree height */
 687         while (root->height > 1 &&
 688                         root->rnode->count == 1 &&
 689                         root->rnode->slots[0]) {
 690                 struct radix_tree_node *to_free = root->rnode;
 691
 692                 root->rnode = to_free->slots[0];
 693                 root->height--;
 694                 /* must only free zeroed nodes into the slab */
 695                 tag_clear(to_free, 0, 0);
 696                 tag_clear(to_free, 1, 0);
 697                 to_free->slots[0] = NULL;
 698                 to_free->count = 0;
 699                 radix_tree_node_free(to_free);
 700         }
 701 }
 702
 703 /**
 704  *      radix_tree_delete    -    delete an item from a radix tree
 705  *      @root:          radix tree root
 706  *      @index:         index key
 707  *
 708  *      Remove the item at @index from the radix tree rooted at @root.
 709  *
 710  *      Returns the address of the deleted item, or NULL if it was not present.
 711  */
 712 void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
 713 {
 714         struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
 715         struct radix_tree_path *orig_pathp;
 716         struct radix_tree_node *slot;
 717         unsigned int height, shift;
 718         void *ret = NULL;
 719         char tags[RADIX_TREE_TAGS];
 720         int nr_cleared_tags;
 721         int tag;
 722         int offset;
 723
 724         height = root->height;
 725         if (index > radix_tree_maxindex(height))
 726                 goto out;
 727
 728         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 729         pathp->node = NULL;
 730         slot = root->rnode;
 731
 732         for ( ; height > 0; height--) {
 733                 if (slot == NULL)
 734                         goto out;
 735
 736                 pathp++;
 737                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 738                 pathp->offset = offset;
 739                 pathp->node = slot;
 740                 slot = slot->slots[offset];
 741                 shift -= RADIX_TREE_MAP_SHIFT;
 742         }
 743
 744         ret = slot;
 745         if (ret == NULL)
 746                 goto out;
 747
 748         orig_pathp = pathp;
 749
 750         /*
 751          * Clear all tags associated with the just-deleted item
 752          */
 753         nr_cleared_tags = 0;
 754         for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
 755                 tags[tag] = 1;
 756                 if (tag_get(pathp->node, tag, pathp->offset)) {
 757                         tag_clear(pathp->node, tag, pathp->offset);
 758                         if (!any_tag_set(pathp->node, tag)) {
 759                                 tags[tag] = 0;
 760                                 nr_cleared_tags++;
 761                         }
 762                 }
 763         }
 764
 765         for (pathp--; nr_cleared_tags && pathp->node; pathp--) {
 766                 for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
 767                         if (tags[tag])
 768                                 continue;
 769
 770                         tag_clear(pathp->node, tag, pathp->offset);
 771                         if (any_tag_set(pathp->node, tag)) {
 772                                 tags[tag] = 1;
 773                                 nr_cleared_tags--;
 774                         }
 775                 }
 776         }
 777
 778         /* Now free the nodes we do not need anymore */
 779         for (pathp = orig_pathp; pathp->node; pathp--) {
 780                 pathp->node->slots[pathp->offset] = NULL;
 781                 pathp->node->count--;
 782
 783                 if (pathp->node->count) {
 784                         if (pathp->node == root->rnode)
 785                                 radix_tree_shrink(root);
 786                         goto out;
 787                 }
 788
 789                 /* Node with zero slots in use so free it */
 790                 radix_tree_node_free(pathp->node);
 791         }
 792         root->rnode = NULL;
 793         root->height = 0;
 794 out:
 795         return ret;
 796 }
 797 EXPORT_SYMBOL(radix_tree_delete);
 798
 799 /**
 800  *      radix_tree_tagged - test whether any items in the tree are tagged
 801  *      @root:          radix tree root
 802  *      @tag:           tag to test
 803  */
 804 int radix_tree_tagged(struct radix_tree_root *root, int tag)
 805 {
 806         struct radix_tree_node *rnode;
 807         rnode = root->rnode;
 808         if (!rnode)
 809                 return 0;
 810         return any_tag_set(rnode, tag);
 811 }
 812 EXPORT_SYMBOL(radix_tree_tagged);
 813
 814 static void
 815 radix_tree_node_ctor(void *node, kmem_cache_t *cachep, unsigned long flags)
 816 {
 817         memset(node, 0, sizeof(struct radix_tree_node));
 818 }
 819
 820 static __init unsigned long __maxindex(unsigned int height)
 821 {
 822         unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
 823         unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
 824
 825         if (tmp >= RADIX_TREE_INDEX_BITS)
 826                 index = ~0UL;
 827         return index;
 828 }
 829
 830 static __init void radix_tree_init_maxindex(void)
 831 {
 832         unsigned int i;
 833
 834         for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
 835                 height_to_maxindex[i] = __maxindex(i);
 836 }
 837
 838 #ifdef CONFIG_HOTPLUG_CPU
 839 static int radix_tree_callback(struct notifier_block *nfb,
 840                             unsigned long action,
 841                             void *hcpu)
 842 {
 843        int cpu = (long)hcpu;
 844        struct radix_tree_preload *rtp;
 845
 846        /* Free per-cpu pool of perloaded nodes */
 847        if (action == CPU_DEAD) {
 848                rtp = &per_cpu(radix_tree_preloads, cpu);
 849                while (rtp->nr) {
 850                        kmem_cache_free(radix_tree_node_cachep,
 851                                        rtp->nodes[rtp->nr-1]);
 852                        rtp->nodes[rtp->nr-1] = NULL;
 853                        rtp->nr--;
 854                }
 855        }
 856        return NOTIFY_OK;
 857 }
 858 #endif /* CONFIG_HOTPLUG_CPU */
 859
 860 void __init radix_tree_init(void)
 861 {
 862         radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
 863                         sizeof(struct radix_tree_node), 0,
 864                         SLAB_PANIC, radix_tree_node_ctor, NULL);
 865         radix_tree_init_maxindex();
 866         hotcpu_notifier(radix_tree_callback, 0);
 867 }