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 struct dm_btree_value_type le64_type = {
 143         .context = NULL,
 144         .size = sizeof(__le64),
 145         .inc = NULL,
 146         .dec = NULL,
 147         .equal = NULL
 148 };
 149
 150 static int init_child(struct dm_btree_info *info, struct btree_node *parent,
 151                       unsigned index, struct child *result)
 152 {
 153         int r, inc;
 154         dm_block_t root;
 155
 156         result->index = index;
 157         root = value64(parent, index);
 158
 159         r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
 160                                &result->block, &inc);
 161         if (r)
 162                 return r;
 163
 164         result->n = dm_block_data(result->block);
 165
 166         if (inc)
 167                 inc_children(info->tm, result->n, &le64_type);
 168
 169         *((__le64 *) value_ptr(parent, index)) =
 170                 cpu_to_le64(dm_block_location(result->block));
 171
 172         return 0;
 173 }
 174
 175 static int exit_child(struct dm_btree_info *info, struct child *c)
 176 {
 177         return dm_tm_unlock(info->tm, c->block);
 178 }
 179
 180 static void shift(struct btree_node *left, struct btree_node *right, int count)
 181 {
 182         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 183         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 184         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 185         uint32_t r_max_entries = le32_to_cpu(right->header.max_entries);
 186
 187         BUG_ON(max_entries != r_max_entries);
 188         BUG_ON(nr_left - count > max_entries);
 189         BUG_ON(nr_right + count > max_entries);
 190
 191         if (!count)
 192                 return;
 193
 194         if (count > 0) {
 195                 node_shift(right, count);
 196                 node_copy(left, right, count);
 197         } else {
 198                 node_copy(left, right, count);
 199                 node_shift(right, count);
 200         }
 201
 202         left->header.nr_entries = cpu_to_le32(nr_left - count);
 203         right->header.nr_entries = cpu_to_le32(nr_right + count);
 204 }
 205
 206 static void __rebalance2(struct dm_btree_info *info, struct btree_node *parent,
 207                          struct child *l, struct child *r)
 208 {
 209         struct btree_node *left = l->n;
 210         struct btree_node *right = r->n;
 211         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 212         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 213         unsigned threshold = 2 * merge_threshold(left) + 1;
 214
 215         if (nr_left + nr_right < threshold) {
 216                 /*
 217                  * Merge
 218                  */
 219                 node_copy(left, right, -nr_right);
 220                 left->header.nr_entries = cpu_to_le32(nr_left + nr_right);
 221                 delete_at(parent, r->index);
 222
 223                 /*
 224                  * We need to decrement the right block, but not it's
 225                  * children, since they're still referenced by left.
 226                  */
 227                 dm_tm_dec(info->tm, dm_block_location(r->block));
 228         } else {
 229                 /*
 230                  * Rebalance.
 231                  */
 232                 unsigned target_left = (nr_left + nr_right) / 2;
 233                 shift(left, right, nr_left - target_left);
 234                 *key_ptr(parent, r->index) = right->keys[0];
 235         }
 236 }
 237
 238 static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
 239                       unsigned left_index)
 240 {
 241         int r;
 242         struct btree_node *parent;
 243         struct child left, right;
 244
 245         parent = dm_block_data(shadow_current(s));
 246
 247         r = init_child(info, parent, left_index, &left);
 248         if (r)
 249                 return r;
 250
 251         r = init_child(info, parent, left_index + 1, &right);
 252         if (r) {
 253                 exit_child(info, &left);
 254                 return r;
 255         }
 256
 257         __rebalance2(info, parent, &left, &right);
 258
 259         r = exit_child(info, &left);
 260         if (r) {
 261                 exit_child(info, &right);
 262                 return r;
 263         }
 264
 265         return exit_child(info, &right);
 266 }
 267
 268 /*
 269  * We dump as many entries from center as possible into left, then the rest
 270  * in right, then rebalance2.  This wastes some cpu, but I want something
 271  * simple atm.
 272  */
 273 static void delete_center_node(struct dm_btree_info *info, struct btree_node *parent,
 274                                struct child *l, struct child *c, struct child *r,
 275                                struct btree_node *left, struct btree_node *center, struct btree_node *right,
 276                                uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
 277 {
 278         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 279         unsigned shift = min(max_entries - nr_left, nr_center);
 280
 281         BUG_ON(nr_left + shift > max_entries);
 282         node_copy(left, center, -shift);
 283         left->header.nr_entries = cpu_to_le32(nr_left + shift);
 284
 285         if (shift != nr_center) {
 286                 shift = nr_center - shift;
 287                 BUG_ON((nr_right + shift) > max_entries);
 288                 node_shift(right, shift);
 289                 node_copy(center, right, shift);
 290                 right->header.nr_entries = cpu_to_le32(nr_right + shift);
 291         }
 292         *key_ptr(parent, r->index) = right->keys[0];
 293
 294         delete_at(parent, c->index);
 295         r->index--;
 296
 297         dm_tm_dec(info->tm, dm_block_location(c->block));
 298         __rebalance2(info, parent, l, r);
 299 }
 300
 301 /*
 302  * Redistributes entries among 3 sibling nodes.
 303  */
 304 static void redistribute3(struct dm_btree_info *info, struct btree_node *parent,
 305                           struct child *l, struct child *c, struct child *r,
 306                           struct btree_node *left, struct btree_node *center, struct btree_node *right,
 307                           uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
 308 {
 309         int s;
 310         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 311         unsigned target = (nr_left + nr_center + nr_right) / 3;
 312         BUG_ON(target > max_entries);
 313
 314         if (nr_left < nr_right) {
 315                 s = nr_left - target;
 316
 317                 if (s < 0 && nr_center < -s) {
 318                         /* not enough in central node */
 319                         shift(left, center, nr_center);
 320                         s = nr_center - target;
 321                         shift(left, right, s);
 322                         nr_right += s;
 323                 } else
 324                         shift(left, center, s);
 325
 326                 shift(center, right, target - nr_right);
 327
 328         } else {
 329                 s = target - nr_right;
 330                 if (s > 0 && nr_center < s) {
 331                         /* not enough in central node */
 332                         shift(center, right, nr_center);
 333                         s = target - nr_center;
 334                         shift(left, right, s);
 335                         nr_left -= s;
 336                 } else
 337                         shift(center, right, s);
 338
 339                 shift(left, center, nr_left - target);
 340         }
 341
 342         *key_ptr(parent, c->index) = center->keys[0];
 343         *key_ptr(parent, r->index) = right->keys[0];
 344 }
 345
 346 static void __rebalance3(struct dm_btree_info *info, struct btree_node *parent,
 347                          struct child *l, struct child *c, struct child *r)
 348 {
 349         struct btree_node *left = l->n;
 350         struct btree_node *center = c->n;
 351         struct btree_node *right = r->n;
 352
 353         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 354         uint32_t nr_center = le32_to_cpu(center->header.nr_entries);
 355         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 356
 357         unsigned threshold = merge_threshold(left) * 4 + 1;
 358
 359         BUG_ON(left->header.max_entries != center->header.max_entries);
 360         BUG_ON(center->header.max_entries != right->header.max_entries);
 361
 362         if ((nr_left + nr_center + nr_right) < threshold)
 363                 delete_center_node(info, parent, l, c, r, left, center, right,
 364                                    nr_left, nr_center, nr_right);
 365         else
 366                 redistribute3(info, parent, l, c, r, left, center, right,
 367                               nr_left, nr_center, nr_right);
 368 }
 369
 370 static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
 371                       unsigned left_index)
 372 {
 373         int r;
 374         struct btree_node *parent = dm_block_data(shadow_current(s));
 375         struct child left, center, right;
 376
 377         /*
 378          * FIXME: fill out an array?
 379          */
 380         r = init_child(info, parent, left_index, &left);
 381         if (r)
 382                 return r;
 383
 384         r = init_child(info, parent, left_index + 1, &center);
 385         if (r) {
 386                 exit_child(info, &left);
 387                 return r;
 388         }
 389
 390         r = init_child(info, parent, left_index + 2, &right);
 391         if (r) {
 392                 exit_child(info, &left);
 393                 exit_child(info, &center);
 394                 return r;
 395         }
 396
 397         __rebalance3(info, parent, &left, &center, &right);
 398
 399         r = exit_child(info, &left);
 400         if (r) {
 401                 exit_child(info, &center);
 402                 exit_child(info, &right);
 403                 return r;
 404         }
 405
 406         r = exit_child(info, &center);
 407         if (r) {
 408                 exit_child(info, &right);
 409                 return r;
 410         }
 411
 412         r = exit_child(info, &right);
 413         if (r)
 414                 return r;
 415
 416         return 0;
 417 }
 418
 419 static int get_nr_entries(struct dm_transaction_manager *tm,
 420                           dm_block_t b, uint32_t *result)
 421 {
 422         int r;
 423         struct dm_block *block;
 424         struct btree_node *n;
 425
 426         r = dm_tm_read_lock(tm, b, &btree_node_validator, &block);
 427         if (r)
 428                 return r;
 429
 430         n = dm_block_data(block);
 431         *result = le32_to_cpu(n->header.nr_entries);
 432
 433         return dm_tm_unlock(tm, block);
 434 }
 435
 436 static int rebalance_children(struct shadow_spine *s,
 437                               struct dm_btree_info *info, uint64_t key)
 438 {
 439         int i, r, has_left_sibling, has_right_sibling;
 440         uint32_t child_entries;
 441         struct btree_node *n;
 442
 443         n = dm_block_data(shadow_current(s));
 444
 445         if (le32_to_cpu(n->header.nr_entries) == 1) {
 446                 struct dm_block *child;
 447                 dm_block_t b = value64(n, 0);
 448
 449                 r = dm_tm_read_lock(info->tm, b, &btree_node_validator, &child);
 450                 if (r)
 451                         return r;
 452
 453                 memcpy(n, dm_block_data(child),
 454                        dm_bm_block_size(dm_tm_get_bm(info->tm)));
 455                 r = dm_tm_unlock(info->tm, child);
 456                 if (r)
 457                         return r;
 458
 459                 dm_tm_dec(info->tm, dm_block_location(child));
 460                 return 0;
 461         }
 462
 463         i = lower_bound(n, key);
 464         if (i < 0)
 465                 return -ENODATA;
 466
 467         r = get_nr_entries(info->tm, value64(n, i), &child_entries);
 468         if (r)
 469                 return r;
 470
 471         has_left_sibling = i > 0;
 472         has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 1);
 473
 474         if (!has_left_sibling)
 475                 r = rebalance2(s, info, i);
 476
 477         else if (!has_right_sibling)
 478                 r = rebalance2(s, info, i - 1);
 479
 480         else
 481                 r = rebalance3(s, info, i - 1);
 482
 483         return r;
 484 }
 485
 486 static int do_leaf(struct btree_node *n, uint64_t key, unsigned *index)
 487 {
 488         int i = lower_bound(n, key);
 489
 490         if ((i < 0) ||
 491             (i >= le32_to_cpu(n->header.nr_entries)) ||
 492             (le64_to_cpu(n->keys[i]) != key))
 493                 return -ENODATA;
 494
 495         *index = i;
 496
 497         return 0;
 498 }
 499
 500 /*
 501  * Prepares for removal from one level of the hierarchy.  The caller must
 502  * call delete_at() to remove the entry at index.
 503  */
 504 static int remove_raw(struct shadow_spine *s, struct dm_btree_info *info,
 505                       struct dm_btree_value_type *vt, dm_block_t root,
 506                       uint64_t key, unsigned *index)
 507 {
 508         int i = *index, r;
 509         struct btree_node *n;
 510
 511         for (;;) {
 512                 r = shadow_step(s, root, vt);
 513                 if (r < 0)
 514                         break;
 515
 516                 /*
 517                  * We have to patch up the parent node, ugly, but I don't
 518                  * see a way to do this automatically as part of the spine
 519                  * op.
 520                  */
 521                 if (shadow_has_parent(s)) {
 522                         __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
 523                         memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
 524                                &location, sizeof(__le64));
 525                 }
 526
 527                 n = dm_block_data(shadow_current(s));
 528
 529                 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
 530                         return do_leaf(n, key, index);
 531
 532                 r = rebalance_children(s, info, key);
 533                 if (r)
 534                         break;
 535
 536                 n = dm_block_data(shadow_current(s));
 537                 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
 538                         return do_leaf(n, key, index);
 539
 540                 i = lower_bound(n, key);
 541
 542                 /*
 543                  * We know the key is present, or else
 544                  * rebalance_children would have returned
 545                  * -ENODATA
 546                  */
 547                 root = value64(n, i);
 548         }
 549
 550         return r;
 551 }
 552
 553 int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
 554                     uint64_t *keys, dm_block_t *new_root)
 555 {
 556         unsigned level, last_level = info->levels - 1;
 557         int index = 0, r = 0;
 558         struct shadow_spine spine;
 559         struct btree_node *n;
 560
 561         init_shadow_spine(&spine, info);
 562         for (level = 0; level < info->levels; level++) {
 563                 r = remove_raw(&spine, info,
 564                                (level == last_level ?
 565                                 &info->value_type : &le64_type),
 566                                root, keys[level], (unsigned *)&index);
 567                 if (r < 0)
 568                         break;
 569
 570                 n = dm_block_data(shadow_current(&spine));
 571                 if (level != last_level) {
 572                         root = value64(n, index);
 573                         continue;
 574                 }
 575
 576                 BUG_ON(index < 0 || index >= le32_to_cpu(n->header.nr_entries));
 577
 578                 if (info->value_type.dec)
 579                         info->value_type.dec(info->value_type.context,
 580                                              value_ptr(n, index));
 581
 582                 delete_at(n, index);
 583         }
 584
 585         *new_root = shadow_root(&spine);
 586         exit_shadow_spine(&spine);
 587
 588         return r;
 589 }
 590 EXPORT_SYMBOL_GPL(dm_btree_remove);