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