drivers/md/persistent-data/dm-btree-remove.c

   1 /*
   2  * Copyright (C) 2011 Red Hat, Inc.
   3  *
   4  * This file is released under the GPL.
   5  */
   6
   7 #include "dm-btree.h"
   8 #include "dm-btree-internal.h"
   9 #include "dm-transaction-manager.h"
  10
  11 #include <linux/export.h>
  12
  13 /*
  14  * Removing an entry from a btree
  15  * ==============================
  16  *
  17  * A very important constraint for our btree is that no node, except the
  18  * root, may have fewer than a certain number of entries.
  19  * (MIN_ENTRIES <= nr_entries <= MAX_ENTRIES).
  20  *
  21  * Ensuring this is complicated by the way we want to only ever hold the
  22  * locks on 2 nodes concurrently, and only change nodes in a top to bottom
  23  * fashion.
  24  *
  25  * Each node may have a left or right sibling.  When decending the spine,
  26  * if a node contains only MIN_ENTRIES then we try and increase this to at
  27  * least MIN_ENTRIES + 1.  We do this in the following ways:
  28  *
  29  * [A] No siblings => this can only happen if the node is the root, in which
  30  *     case we copy the childs contents over the root.
  31  *
  32  * [B] No left sibling
  33  *     ==> rebalance(node, right sibling)
  34  *
  35  * [C] No right sibling
  36  *     ==> rebalance(left sibling, node)
  37  *
  38  * [D] Both siblings, total_entries(left, node, right) <= DEL_THRESHOLD
  39  *     ==> delete node adding it's contents to left and right
  40  *
  41  * [E] Both siblings, total_entries(left, node, right) > DEL_THRESHOLD
  42  *     ==> rebalance(left, node, right)
  43  *
  44  * After these operations it's possible that the our original node no
  45  * longer contains the desired sub tree.  For this reason this rebalancing
  46  * is performed on the children of the current node.  This also avoids
  47  * having a special case for the root.
  48  *
  49  * Once this rebalancing has occurred we can then step into the child node
  50  * for internal nodes.  Or delete the entry for leaf nodes.
  51  */
  52
  53 /*
  54  * Some little utilities for moving node data around.
  55  */
  56 static void node_shift(struct btree_node *n, int shift)
  57 {
  58         uint32_t nr_entries = le32_to_cpu(n->header.nr_entries);
  59         uint32_t value_size = le32_to_cpu(n->header.value_size);
  60
  61         if (shift < 0) {
  62                 shift = -shift;
  63                 BUG_ON(shift > nr_entries);
  64                 BUG_ON((void *) key_ptr(n, shift) >= value_ptr(n, shift));
  65                 memmove(key_ptr(n, 0),
  66                         key_ptr(n, shift),
  67                         (nr_entries - shift) * sizeof(__le64));
  68                 memmove(value_ptr(n, 0),
  69                         value_ptr(n, shift),
  70                         (nr_entries - shift) * value_size);
  71         } else {
  72                 BUG_ON(nr_entries + shift > le32_to_cpu(n->header.max_entries));
  73                 memmove(key_ptr(n, shift),
  74                         key_ptr(n, 0),
  75                         nr_entries * sizeof(__le64));
  76                 memmove(value_ptr(n, shift),
  77                         value_ptr(n, 0),
  78                         nr_entries * value_size);
  79         }
  80 }
  81
  82 static void node_copy(struct btree_node *left, struct btree_node *right, int shift)
  83 {
  84         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
  85         uint32_t value_size = le32_to_cpu(left->header.value_size);
  86         BUG_ON(value_size != le32_to_cpu(right->header.value_size));
  87
  88         if (shift < 0) {
  89                 shift = -shift;
  90                 BUG_ON(nr_left + shift > le32_to_cpu(left->header.max_entries));
  91                 memcpy(key_ptr(left, nr_left),
  92                        key_ptr(right, 0),
  93                        shift * sizeof(__le64));
  94                 memcpy(value_ptr(left, nr_left),
  95                        value_ptr(right, 0),
  96                        shift * value_size);
  97         } else {
  98                 BUG_ON(shift > le32_to_cpu(right->header.max_entries));
  99                 memcpy(key_ptr(right, 0),
 100                        key_ptr(left, nr_left - shift),
 101                        shift * sizeof(__le64));
 102                 memcpy(value_ptr(right, 0),
 103                        value_ptr(left, nr_left - shift),
 104                        shift * value_size);
 105         }
 106 }
 107
 108 /*
 109  * Delete a specific entry from a leaf node.
 110  */
 111 static void delete_at(struct btree_node *n, unsigned index)
 112 {
 113         unsigned nr_entries = le32_to_cpu(n->header.nr_entries);
 114         unsigned nr_to_copy = nr_entries - (index + 1);
 115         uint32_t value_size = le32_to_cpu(n->header.value_size);
 116         BUG_ON(index >= nr_entries);
 117
 118         if (nr_to_copy) {
 119                 memmove(key_ptr(n, index),
 120                         key_ptr(n, index + 1),
 121                         nr_to_copy * sizeof(__le64));
 122
 123                 memmove(value_ptr(n, index),
 124                         value_ptr(n, index + 1),
 125                         nr_to_copy * value_size);
 126         }
 127
 128         n->header.nr_entries = cpu_to_le32(nr_entries - 1);
 129 }
 130
 131 static unsigned merge_threshold(struct btree_node *n)
 132 {
 133         return le32_to_cpu(n->header.max_entries) / 3;
 134 }
 135
 136 struct child {
 137         unsigned index;
 138         struct dm_block *block;
 139         struct btree_node *n;
 140 };
 141
 142 static int init_child(struct dm_btree_info *info, struct dm_btree_value_type *vt,
 143                       struct btree_node *parent,
 144                       unsigned index, struct child *result)
 145 {
 146         int r, inc;
 147         dm_block_t root;
 148
 149         result->index = index;
 150         root = value64(parent, index);
 151
 152         r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
 153                                &result->block, &inc);
 154         if (r)
 155                 return r;
 156
 157         result->n = dm_block_data(result->block);
 158
 159         if (inc)
 160                 inc_children(info->tm, result->n, vt);
 161
 162         *((__le64 *) value_ptr(parent, index)) =
 163                 cpu_to_le64(dm_block_location(result->block));
 164
 165         return 0;
 166 }
 167
 168 static int exit_child(struct dm_btree_info *info, struct child *c)
 169 {
 170         return dm_tm_unlock(info->tm, c->block);
 171 }
 172
 173 static void shift(struct btree_node *left, struct btree_node *right, int count)
 174 {
 175         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 176         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 177         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 178         uint32_t r_max_entries = le32_to_cpu(right->header.max_entries);
 179
 180         BUG_ON(max_entries != r_max_entries);
 181         BUG_ON(nr_left - count > max_entries);
 182         BUG_ON(nr_right + count > max_entries);
 183
 184         if (!count)
 185                 return;
 186
 187         if (count > 0) {
 188                 node_shift(right, count);
 189                 node_copy(left, right, count);
 190         } else {
 191                 node_copy(left, right, count);
 192                 node_shift(right, count);
 193         }
 194
 195         left->header.nr_entries = cpu_to_le32(nr_left - count);
 196         right->header.nr_entries = cpu_to_le32(nr_right + count);
 197 }
 198
 199 static void __rebalance2(struct dm_btree_info *info, struct btree_node *parent,
 200                          struct child *l, struct child *r)
 201 {
 202         struct btree_node *left = l->n;
 203         struct btree_node *right = r->n;
 204         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 205         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 206         unsigned threshold = 2 * merge_threshold(left) + 1;
 207
 208         if (nr_left + nr_right < threshold) {
 209                 /*
 210                  * Merge
 211                  */
 212                 node_copy(left, right, -nr_right);
 213                 left->header.nr_entries = cpu_to_le32(nr_left + nr_right);
 214                 delete_at(parent, r->index);
 215
 216                 /*
 217                  * We need to decrement the right block, but not it's
 218                  * children, since they're still referenced by left.
 219                  */
 220                 dm_tm_dec(info->tm, dm_block_location(r->block));
 221         } else {
 222                 /*
 223                  * Rebalance.
 224                  */
 225                 unsigned target_left = (nr_left + nr_right) / 2;
 226                 shift(left, right, nr_left - target_left);
 227                 *key_ptr(parent, r->index) = right->keys[0];
 228         }
 229 }
 230
 231 static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
 232                       struct dm_btree_value_type *vt, unsigned left_index)
 233 {
 234         int r;
 235         struct btree_node *parent;
 236         struct child left, right;
 237
 238         parent = dm_block_data(shadow_current(s));
 239
 240         r = init_child(info, vt, parent, left_index, &left);
 241         if (r)
 242                 return r;
 243
 244         r = init_child(info, vt, parent, left_index + 1, &right);
 245         if (r) {
 246                 exit_child(info, &left);
 247                 return r;
 248         }
 249
 250         __rebalance2(info, parent, &left, &right);
 251
 252         r = exit_child(info, &left);
 253         if (r) {
 254                 exit_child(info, &right);
 255                 return r;
 256         }
 257
 258         return exit_child(info, &right);
 259 }
 260
 261 /*
 262  * We dump as many entries from center as possible into left, then the rest
 263  * in right, then rebalance2.  This wastes some cpu, but I want something
 264  * simple atm.
 265  */
 266 static void delete_center_node(struct dm_btree_info *info, struct btree_node *parent,
 267                                struct child *l, struct child *c, struct child *r,
 268                                struct btree_node *left, struct btree_node *center, struct btree_node *right,
 269                                uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
 270 {
 271         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 272         unsigned shift = min(max_entries - nr_left, nr_center);
 273
 274         BUG_ON(nr_left + shift > max_entries);
 275         node_copy(left, center, -shift);
 276         left->header.nr_entries = cpu_to_le32(nr_left + shift);
 277
 278         if (shift != nr_center) {
 279                 shift = nr_center - shift;
 280                 BUG_ON((nr_right + shift) > max_entries);
 281                 node_shift(right, shift);
 282                 node_copy(center, right, shift);
 283                 right->header.nr_entries = cpu_to_le32(nr_right + shift);
 284         }
 285         *key_ptr(parent, r->index) = right->keys[0];
 286
 287         delete_at(parent, c->index);
 288         r->index--;
 289
 290         dm_tm_dec(info->tm, dm_block_location(c->block));
 291         __rebalance2(info, parent, l, r);
 292 }
 293
 294 /*
 295  * Redistributes entries among 3 sibling nodes.
 296  */
 297 static void redistribute3(struct dm_btree_info *info, struct btree_node *parent,
 298                           struct child *l, struct child *c, struct child *r,
 299                           struct btree_node *left, struct btree_node *center, struct btree_node *right,
 300                           uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
 301 {
 302         int s;
 303         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 304         unsigned target = (nr_left + nr_center + nr_right) / 3;
 305         BUG_ON(target > max_entries);
 306
 307         if (nr_left < nr_right) {
 308                 s = nr_left - target;
 309
 310                 if (s < 0 && nr_center < -s) {
 311                         /* not enough in central node */
 312                         shift(left, center, nr_center);
 313                         s = nr_center - target;
 314                         shift(left, right, s);
 315                         nr_right += s;
 316                 } else
 317                         shift(left, center, s);
 318
 319                 shift(center, right, target - nr_right);
 320
 321         } else {
 322                 s = target - nr_right;
 323                 if (s > 0 && nr_center < s) {
 324                         /* not enough in central node */
 325                         shift(center, right, nr_center);
 326                         s = target - nr_center;
 327                         shift(left, right, s);
 328                         nr_left -= s;
 329                 } else
 330                         shift(center, right, s);
 331
 332                 shift(left, center, nr_left - target);
 333         }
 334
 335         *key_ptr(parent, c->index) = center->keys[0];
 336         *key_ptr(parent, r->index) = right->keys[0];
 337 }
 338
 339 static void __rebalance3(struct dm_btree_info *info, struct btree_node *parent,
 340                          struct child *l, struct child *c, struct child *r)
 341 {
 342         struct btree_node *left = l->n;
 343         struct btree_node *center = c->n;
 344         struct btree_node *right = r->n;
 345
 346         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 347         uint32_t nr_center = le32_to_cpu(center->header.nr_entries);
 348         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 349
 350         unsigned threshold = merge_threshold(left) * 4 + 1;
 351
 352         BUG_ON(left->header.max_entries != center->header.max_entries);
 353         BUG_ON(center->header.max_entries != right->header.max_entries);
 354
 355         if ((nr_left + nr_center + nr_right) < threshold)
 356                 delete_center_node(info, parent, l, c, r, left, center, right,
 357                                    nr_left, nr_center, nr_right);
 358         else
 359                 redistribute3(info, parent, l, c, r, left, center, right,
 360                               nr_left, nr_center, nr_right);
 361 }
 362
 363 static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
 364                       struct dm_btree_value_type *vt, unsigned left_index)
 365 {
 366         int r;
 367         struct btree_node *parent = dm_block_data(shadow_current(s));
 368         struct child left, center, right;
 369
 370         /*
 371          * FIXME: fill out an array?
 372          */
 373         r = init_child(info, vt, parent, left_index, &left);
 374         if (r)
 375                 return r;
 376
 377         r = init_child(info, vt, parent, left_index + 1, &center);
 378         if (r) {
 379                 exit_child(info, &left);
 380                 return r;
 381         }
 382
 383         r = init_child(info, vt, parent, left_index + 2, &right);
 384         if (r) {
 385                 exit_child(info, &left);
 386                 exit_child(info, &center);
 387                 return r;
 388         }
 389
 390         __rebalance3(info, parent, &left, &center, &right);
 391
 392         r = exit_child(info, &left);
 393         if (r) {
 394                 exit_child(info, &center);
 395                 exit_child(info, &right);
 396                 return r;
 397         }
 398
 399         r = exit_child(info, &center);
 400         if (r) {
 401                 exit_child(info, &right);
 402                 return r;
 403         }
 404
 405         r = exit_child(info, &right);
 406         if (r)
 407                 return r;
 408
 409         return 0;
 410 }
 411
 412 static int get_nr_entries(struct dm_transaction_manager *tm,
 413                           dm_block_t b, uint32_t *result)
 414 {
 415         int r;
 416         struct dm_block *block;
 417         struct btree_node *n;
 418
 419         r = dm_tm_read_lock(tm, b, &btree_node_validator, &block);
 420         if (r)
 421                 return r;
 422
 423         n = dm_block_data(block);
 424         *result = le32_to_cpu(n->header.nr_entries);
 425
 426         return dm_tm_unlock(tm, block);
 427 }
 428
 429 static int rebalance_children(struct shadow_spine *s,
 430                               struct dm_btree_info *info,
 431                               struct dm_btree_value_type *vt, uint64_t key)
 432 {
 433         int i, r, has_left_sibling, has_right_sibling;
 434         uint32_t child_entries;
 435         struct btree_node *n;
 436
 437         n = dm_block_data(shadow_current(s));
 438
 439         if (le32_to_cpu(n->header.nr_entries) == 1) {
 440                 struct dm_block *child;
 441                 dm_block_t b = value64(n, 0);
 442
 443                 r = dm_tm_read_lock(info->tm, b, &btree_node_validator, &child);
 444                 if (r)
 445                         return r;
 446
 447                 memcpy(n, dm_block_data(child),
 448                        dm_bm_block_size(dm_tm_get_bm(info->tm)));
 449                 r = dm_tm_unlock(info->tm, child);
 450                 if (r)
 451                         return r;
 452
 453                 dm_tm_dec(info->tm, dm_block_location(child));
 454                 return 0;
 455         }
 456
 457         i = lower_bound(n, key);
 458         if (i < 0)
 459                 return -ENODATA;
 460
 461         r = get_nr_entries(info->tm, value64(n, i), &child_entries);
 462         if (r)
 463                 return r;
 464
 465         has_left_sibling = i > 0;
 466         has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 1);
 467
 468         if (!has_left_sibling)
 469                 r = rebalance2(s, info, vt, i);
 470
 471         else if (!has_right_sibling)
 472                 r = rebalance2(s, info, vt, i - 1);
 473
 474         else
 475                 r = rebalance3(s, info, vt, i - 1);
 476
 477         return r;
 478 }
 479
 480 static int do_leaf(struct btree_node *n, uint64_t key, unsigned *index)
 481 {
 482         int i = lower_bound(n, key);
 483
 484         if ((i < 0) ||
 485             (i >= le32_to_cpu(n->header.nr_entries)) ||
 486             (le64_to_cpu(n->keys[i]) != key))
 487                 return -ENODATA;
 488
 489         *index = i;
 490
 491         return 0;
 492 }
 493
 494 /*
 495  * Prepares for removal from one level of the hierarchy.  The caller must
 496  * call delete_at() to remove the entry at index.
 497  */
 498 static int remove_raw(struct shadow_spine *s, struct dm_btree_info *info,
 499                       struct dm_btree_value_type *vt, dm_block_t root,
 500                       uint64_t key, unsigned *index)
 501 {
 502         int i = *index, r;
 503         struct btree_node *n;
 504
 505         for (;;) {
 506                 r = shadow_step(s, root, vt);
 507                 if (r < 0)
 508                         break;
 509
 510                 /*
 511                  * We have to patch up the parent node, ugly, but I don't
 512                  * see a way to do this automatically as part of the spine
 513                  * op.
 514                  */
 515                 if (shadow_has_parent(s)) {
 516                         __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
 517                         memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
 518                                &location, sizeof(__le64));
 519                 }
 520
 521                 n = dm_block_data(shadow_current(s));
 522
 523                 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
 524                         return do_leaf(n, key, index);
 525
 526                 r = rebalance_children(s, info, vt, key);
 527                 if (r)
 528                         break;
 529
 530                 n = dm_block_data(shadow_current(s));
 531                 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
 532                         return do_leaf(n, key, index);
 533
 534                 i = lower_bound(n, key);
 535
 536                 /*
 537                  * We know the key is present, or else
 538                  * rebalance_children would have returned
 539                  * -ENODATA
 540                  */
 541                 root = value64(n, i);
 542         }
 543
 544         return r;
 545 }
 546
 547 static struct dm_btree_value_type le64_type = {
 548         .context = NULL,
 549         .size = sizeof(__le64),
 550         .inc = NULL,
 551         .dec = NULL,
 552         .equal = NULL
 553 };
 554
 555 int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
 556                     uint64_t *keys, dm_block_t *new_root)
 557 {
 558         unsigned level, last_level = info->levels - 1;
 559         int index = 0, r = 0;
 560         struct shadow_spine spine;
 561         struct btree_node *n;
 562
 563         init_shadow_spine(&spine, info);
 564         for (level = 0; level < info->levels; level++) {
 565                 r = remove_raw(&spine, info,
 566                                (level == last_level ?
 567                                 &info->value_type : &le64_type),
 568                                root, keys[level], (unsigned *)&index);
 569                 if (r < 0)
 570                         break;
 571
 572                 n = dm_block_data(shadow_current(&spine));
 573                 if (level != last_level) {
 574                         root = value64(n, index);
 575                         continue;
 576                 }
 577
 578                 BUG_ON(index < 0 || index >= le32_to_cpu(n->header.nr_entries));
 579
 580                 if (info->value_type.dec)
 581                         info->value_type.dec(info->value_type.context,
 582                                              value_ptr(n, index));
 583
 584                 delete_at(n, index);
 585         }
 586
 587         *new_root = shadow_root(&spine);
 588         exit_shadow_spine(&spine);
 589
 590         return r;
 591 }
 592 EXPORT_SYMBOL_GPL(dm_btree_remove);