lustre/ldlm/interval_tree.c

   1 /* -*- mode: c; c-basic-offset: 8; indent-tabs-mode: nil; -*-
   2  * vim:expandtab:shiftwidth=8:tabstop=8:
   3  *
   4  *  Interval tree library used by ldlm extent lock code
   5  *
   6  *  Copyright (c) 2007 Cluster File Systems, Inc.
   7  *   Author: Huang Wei <huangwei@clusterfs.com>
   8  *   Author: Jay Xiong <jinshan.xiong@sun.com>
   9  *
  10  *   This file is part of the Lustre file system, http://www.lustre.org
  11  *   Lustre is a trademark of Cluster File Systems, Inc.
  12  *
  13  *   You may have signed or agreed to another license before downloading
  14  *   this software.  If so, you are bound by the terms and conditions
  15  *   of that agreement, and the following does not apply to you.  See the
  16  *   LICENSE file included with this distribution for more information.
  17  *
  18  *   If you did not agree to a different license, then this copy of Lustre
  19  *   is open source software; you can redistribute it and/or modify it
  20  *   under the terms of version 2 of the GNU General Public License as
  21  *   published by the Free Software Foundation.
  22  *
  23  *   In either case, Lustre is distributed in the hope that it will be
  24  *   useful, but WITHOUT ANY WARRANTY; without even the implied warranty
  25  *   of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  26  *   license text for more details.
  27  */
  28 #ifdef __KERNEL__
  29 # include <lustre_dlm.h>
  30 #else
  31 # include <liblustre.h>
  32 #endif
  33 #include <obd_support.h>
  34 #include <interval_tree.h>
  35
  36 enum {
  37         INTERVAL_RED = 0,
  38         INTERVAL_BLACK = 1
  39 };
  40
  41 static inline int node_is_left_child(struct interval_node *node)
  42 {
  43         LASSERT(node->in_parent != NULL);
  44         return node == node->in_parent->in_left;
  45 }
  46
  47 static inline int node_is_right_child(struct interval_node *node)
  48 {
  49         LASSERT(node->in_parent != NULL);
  50         return node == node->in_parent->in_right;
  51 }
  52
  53 static inline int node_is_red(struct interval_node *node)
  54 {
  55         return node->in_color == INTERVAL_RED;
  56 }
  57
  58 static inline int node_is_black(struct interval_node *node)
  59 {
  60         return node->in_color == INTERVAL_BLACK;
  61 }
  62
  63 static inline int extent_compare(struct interval_node_extent *e1,
  64                                  struct interval_node_extent *e2)
  65 {
  66         int rc;
  67         if (e1->start == e2->start) {
  68                 if (e1->end < e2->end)
  69                         rc = -1;
  70                 else if (e1->end > e2->end)
  71                         rc = 1;
  72                 else
  73                         rc = 0;
  74         } else {
  75                 if (e1->start < e2->start)
  76                         rc = -1;
  77                 else
  78                         rc = 1;
  79         }
  80         return rc;
  81 }
  82
  83 static inline int extent_equal(struct interval_node_extent *e1,
  84                                struct interval_node_extent *e2)
  85 {
  86         return (e1->start == e2->start) && (e1->end == e2->end);
  87 }
  88
  89 static inline int extent_overlapped(struct interval_node_extent *e1,
  90                                     struct interval_node_extent *e2)
  91 {
  92         return (e1->start <= e2->end) && (e2->start <= e1->end);
  93 }
  94
  95 static inline int node_compare(struct interval_node *n1,
  96                                struct interval_node *n2)
  97 {
  98         return extent_compare(&n1->in_extent, &n2->in_extent);
  99 }
 100
 101 static inline int node_equal(struct interval_node *n1,
 102                              struct interval_node *n2)
 103 {
 104         return extent_equal(&n1->in_extent, &n2->in_extent);
 105 }
 106
 107 static inline __u64 max_u64(__u64 x, __u64 y)
 108 {
 109         return x > y ? x : y;
 110 }
 111
 112 static inline __u64 min_u64(__u64 x, __u64 y)
 113 {
 114         return x < y ? x : y;
 115 }
 116
 117 #define interval_for_each(node, root)                   \
 118 for (node = interval_first(root); node != NULL;         \
 119      node = interval_next(node))
 120
 121 #define interval_for_each_reverse(node, root)           \
 122 for (node = interval_last(root); node != NULL;          \
 123      node = interval_prev(node))
 124
 125 static struct interval_node *interval_first(struct interval_node *node)
 126 {
 127         ENTRY;
 128
 129         if (!node)
 130                 RETURN(NULL);
 131         while (node->in_left)
 132                 node = node->in_left;
 133         RETURN(node);
 134 }
 135
 136 static struct interval_node *interval_last(struct interval_node *node)
 137 {
 138         ENTRY;
 139
 140         if (!node)
 141                 RETURN(NULL);
 142         while (node->in_right)
 143                 node = node->in_right;
 144         RETURN(node);
 145 }
 146
 147 static struct interval_node *interval_next(struct interval_node *node)
 148 {
 149         ENTRY;
 150
 151         if (!node)
 152                 RETURN(NULL);
 153         if (node->in_right)
 154                 RETURN(interval_first(node->in_right));
 155         while (node->in_parent && node_is_right_child(node))
 156                 node = node->in_parent;
 157         RETURN(node->in_parent);
 158 }
 159
 160 static struct interval_node *interval_prev(struct interval_node *node)
 161 {
 162         ENTRY;
 163
 164         if (!node)
 165                 RETURN(NULL);
 166
 167         if (node->in_left)
 168                 RETURN(interval_last(node->in_left));
 169
 170         while (node->in_parent && node_is_left_child(node))
 171                 node = node->in_parent;
 172
 173         RETURN(node->in_parent);
 174 }
 175
 176 enum interval_iter interval_iterate(struct interval_node *root,
 177                                     interval_callback_t func,
 178                                     void *data)
 179 {
 180         struct interval_node *node;
 181         enum interval_iter rc = INTERVAL_ITER_CONT;
 182         ENTRY;
 183
 184         interval_for_each(node, root) {
 185                 rc = func(node, data);
 186                 if (rc == INTERVAL_ITER_STOP)
 187                         break;
 188         }
 189
 190         RETURN(rc);
 191 }
 192 EXPORT_SYMBOL(interval_iterate);
 193
 194 enum interval_iter interval_iterate_reverse(struct interval_node *root,
 195                                             interval_callback_t func,
 196                                             void *data)
 197 {
 198         struct interval_node *node;
 199         enum interval_iter rc = INTERVAL_ITER_CONT;
 200         ENTRY;
 201
 202         interval_for_each_reverse(node, root) {
 203                 rc = func(node, data);
 204                 if (rc == INTERVAL_ITER_STOP)
 205                         break;
 206         }
 207
 208         RETURN(rc);
 209 }
 210 EXPORT_SYMBOL(interval_iterate_reverse);
 211
 212 /* try to find a node with same interval in the tree,
 213  * if found, return the pointer to the node, otherwise return NULL*/
 214 struct interval_node *interval_find(struct interval_node *root,
 215                                     struct interval_node_extent *ex)
 216 {
 217         struct interval_node *walk = root;
 218         int rc;
 219         ENTRY;
 220
 221         while (walk) {
 222                 rc = extent_compare(ex, &walk->in_extent);
 223                 if (rc == 0)
 224                         break;
 225                 else if (rc < 0)
 226                         walk = walk->in_left;
 227                 else
 228                         walk = walk->in_right;
 229         }
 230
 231         RETURN(walk);
 232 }
 233 EXPORT_SYMBOL(interval_find);
 234
 235 static void __rotate_change_maxhigh(struct interval_node *node,
 236                                     struct interval_node *rotate)
 237 {
 238         __u64 left_max, right_max;
 239
 240         rotate->in_max_high = node->in_max_high;
 241         left_max = node->in_left ? node->in_left->in_max_high : 0;
 242         right_max = node->in_right ? node->in_right->in_max_high : 0;
 243         node->in_max_high  = max_u64(interval_high(node),
 244                                      max_u64(left_max,right_max));
 245 }
 246
 247 /* The left rotation "pivots" around the link from node to node->right, and
 248  * - node will be linked to node->right's left child, and
 249  * - node->right's left child will be linked to node's right child.  */
 250 static void __rotate_left(struct interval_node *node,
 251                           struct interval_node **root)
 252 {
 253         struct interval_node *right = node->in_right;
 254         struct interval_node *parent = node->in_parent;
 255
 256         node->in_right = right->in_left;
 257         if (node->in_right)
 258                 right->in_left->in_parent = node;
 259
 260         right->in_left = node;
 261         right->in_parent = parent;
 262         if (parent) {
 263                 if (node_is_left_child(node))
 264                         parent->in_left = right;
 265                 else
 266                         parent->in_right = right;
 267         } else {
 268                 *root = right;
 269         }
 270         node->in_parent = right;
 271
 272         /* update max_high for node and right */
 273         __rotate_change_maxhigh(node, right);
 274 }
 275
 276 /* The right rotation "pivots" around the link from node to node->left, and
 277  * - node will be linked to node->left's right child, and
 278  * - node->left's right child will be linked to node's left child.  */
 279 static void __rotate_right(struct interval_node *node,
 280                            struct interval_node **root)
 281 {
 282         struct interval_node *left = node->in_left;
 283         struct interval_node *parent = node->in_parent;
 284
 285         node->in_left = left->in_right;
 286         if (node->in_left)
 287                 left->in_right->in_parent = node;
 288         left->in_right = node;
 289
 290         left->in_parent = parent;
 291         if (parent) {
 292                 if (node_is_right_child(node))
 293                         parent->in_right = left;
 294                 else
 295                         parent->in_left = left;
 296         } else {
 297                 *root = left;
 298         }
 299         node->in_parent = left;
 300
 301         /* update max_high for node and left */
 302         __rotate_change_maxhigh(node, left);
 303 }
 304
 305 #define interval_swap(a, b) do {                        \
 306         struct interval_node *c = a; a = b; b = c;      \
 307 } while (0)
 308
 309 /*
 310  * Operations INSERT and DELETE, when run on a tree with n keys,
 311  * take O(logN) time.Because they modify the tree, the result
 312  * may violate the red-black properties.To restore these properties,
 313  * we must change the colors of some of the nodes in the tree
 314  * and also change the pointer structure.
 315  */
 316 static void interval_insert_color(struct interval_node *node,
 317                                   struct interval_node **root)
 318 {
 319         struct interval_node *parent, *gparent;
 320         ENTRY;
 321
 322         while ((parent = node->in_parent) && node_is_red(parent)) {
 323                 gparent = parent->in_parent;
 324                 /* Parent is RED, so gparent must not be NULL */
 325                 if (node_is_left_child(parent)) {
 326                         struct interval_node *uncle;
 327                         uncle = gparent->in_right;
 328                         if (uncle && node_is_red(uncle)) {
 329                                 uncle->in_color = INTERVAL_BLACK;
 330                                 parent->in_color = INTERVAL_BLACK;
 331                                 gparent->in_color = INTERVAL_RED;
 332                                 node = gparent;
 333                                 continue;
 334                         }
 335
 336                         if (parent->in_right == node) {
 337                                 __rotate_left(parent, root);
 338                                 interval_swap(node, parent);
 339                         }
 340
 341                         parent->in_color = INTERVAL_BLACK;
 342                         gparent->in_color = INTERVAL_RED;
 343                         __rotate_right(gparent, root);
 344                 } else {
 345                         struct interval_node *uncle;
 346                         uncle = gparent->in_left;
 347                         if (uncle && node_is_red(uncle)) {
 348                                 uncle->in_color = INTERVAL_BLACK;
 349                                 parent->in_color = INTERVAL_BLACK;
 350                                 gparent->in_color = INTERVAL_RED;
 351                                 node = gparent;
 352                                 continue;
 353                         }
 354
 355                         if (node_is_left_child(node)) {
 356                                 __rotate_right(parent, root);
 357                                 interval_swap(node, parent);
 358                         }
 359
 360                         parent->in_color = INTERVAL_BLACK;
 361                         gparent->in_color = INTERVAL_RED;
 362                         __rotate_left(gparent, root);
 363                 }
 364         }
 365
 366         (*root)->in_color = INTERVAL_BLACK;
 367         EXIT;
 368 }
 369
 370 struct interval_node *interval_insert(struct interval_node *node,
 371                                       struct interval_node **root)
 372
 373 {
 374         struct interval_node **p, *parent = NULL;
 375         ENTRY;
 376
 377         p = root;
 378         while (*p) {
 379                 parent = *p;
 380                 if (node_equal(parent, node))
 381                         RETURN(parent);
 382
 383                 /* max_high field must be updated after each iteration */
 384                 if (parent->in_max_high < interval_high(node))
 385                         parent->in_max_high = interval_high(node);
 386
 387                 if (node_compare(node, parent) < 0)
 388                         p = &parent->in_left;
 389                 else
 390                         p = &parent->in_right;
 391         }
 392
 393         /* link node into the tree */
 394         node->in_parent = parent;
 395         node->in_color = INTERVAL_RED;
 396         node->in_left = node->in_right = NULL;
 397         *p = node;
 398
 399         interval_insert_color(node, root);
 400
 401         RETURN(NULL);
 402 }
 403 EXPORT_SYMBOL(interval_insert);
 404
 405 static inline int node_is_black_or_0(struct interval_node *node)
 406 {
 407         return !node || node_is_black(node);
 408 }
 409
 410 static void interval_erase_color(struct interval_node *node,
 411                                  struct interval_node *parent,
 412                                  struct interval_node **root)
 413 {
 414         struct interval_node *tmp;
 415         ENTRY;
 416
 417         while (node_is_black_or_0(node) && node != *root) {
 418                 if (parent->in_left == node) {
 419                         tmp = parent->in_right;
 420                         if (node_is_red(tmp)) {
 421                                 tmp->in_color = INTERVAL_BLACK;
 422                                 parent->in_color = INTERVAL_RED;
 423                                 __rotate_left(parent, root);
 424                                 tmp = parent->in_right;
 425                         }
 426                         if (node_is_black_or_0(tmp->in_left) &&
 427                             node_is_black_or_0(tmp->in_right)) {
 428                                 tmp->in_color = INTERVAL_RED;
 429                                 node = parent;
 430                                 parent = node->in_parent;
 431                         } else {
 432                                 if (node_is_black_or_0(tmp->in_right)) {
 433                                         struct interval_node *o_left;
 434                                         if ((o_left = tmp->in_left))
 435                                              o_left->in_color = INTERVAL_BLACK;
 436                                         tmp->in_color = INTERVAL_RED;
 437                                         __rotate_right(tmp, root);
 438                                         tmp = parent->in_right;
 439                                 }
 440                                 tmp->in_color = parent->in_color;
 441                                 parent->in_color = INTERVAL_BLACK;
 442                                 if (tmp->in_right)
 443                                     tmp->in_right->in_color = INTERVAL_BLACK;
 444                                 __rotate_left(parent, root);
 445                                 node = *root;
 446                                 break;
 447                         }
 448                 } else {
 449                         tmp = parent->in_left;
 450                         if (node_is_red(tmp)) {
 451                                 tmp->in_color = INTERVAL_BLACK;
 452                                 parent->in_color = INTERVAL_RED;
 453                                 __rotate_right(parent, root);
 454                                 tmp = parent->in_left;
 455                         }
 456                         if (node_is_black_or_0(tmp->in_left) &&
 457                             node_is_black_or_0(tmp->in_right)) {
 458                                 tmp->in_color = INTERVAL_RED;
 459                                 node = parent;
 460                                 parent = node->in_parent;
 461                         } else {
 462                                 if (node_is_black_or_0(tmp->in_left)) {
 463                                         struct interval_node *o_right;
 464                                         if ((o_right = tmp->in_right))
 465                                             o_right->in_color = INTERVAL_BLACK;
 466                                         tmp->in_color = INTERVAL_RED;
 467                                         __rotate_left(tmp, root);
 468                                         tmp = parent->in_left;
 469                                 }
 470                                 tmp->in_color = parent->in_color;
 471                                 parent->in_color = INTERVAL_BLACK;
 472                                 if (tmp->in_left)
 473                                         tmp->in_left->in_color = INTERVAL_BLACK;
 474                                 __rotate_right(parent, root);
 475                                 node = *root;
 476                                 break;
 477                         }
 478                 }
 479         }
 480         if (node)
 481                 node->in_color = INTERVAL_BLACK;
 482         EXIT;
 483 }
 484
 485 /*
 486  * if the @max_high value of @node is changed, this function traverse  a path
 487  * from node  up to the root to update max_high for the whole tree.
 488  */
 489 static void update_maxhigh(struct interval_node *node,
 490                            __u64  old_maxhigh)
 491 {
 492         __u64 left_max, right_max;
 493         ENTRY;
 494
 495         while (node) {
 496                 left_max = node->in_left ? node->in_left->in_max_high : 0;
 497                 right_max = node->in_right ? node->in_right->in_max_high : 0;
 498                 node->in_max_high = max_u64(interval_high(node),
 499                                             max_u64(left_max, right_max));
 500
 501                 if (node->in_max_high >= old_maxhigh)
 502                         break;
 503                 node = node->in_parent;
 504         }
 505         EXIT;
 506 }
 507
 508 void interval_erase(struct interval_node *node,
 509                     struct interval_node **root)
 510 {
 511         struct interval_node *child, *parent;
 512         int color;
 513         ENTRY;
 514
 515         if (!node->in_left) {
 516                 child = node->in_right;
 517         } else if (!node->in_right) {
 518                 child = node->in_left;
 519         } else { /* Both left and right child are not NULL */
 520                 struct interval_node *old = node;
 521
 522                 node = interval_next(node);
 523                 child = node->in_right;
 524                 parent = node->in_parent;
 525                 color = node->in_color;
 526
 527                 if (child)
 528                         child->in_parent = parent;
 529                 if (parent == old) {
 530                         parent->in_right = child;
 531                         parent = node;
 532                 } else {
 533                         parent->in_left = child;
 534                 }
 535
 536                 node->in_color = old->in_color;
 537                 node->in_right = old->in_right;
 538                 node->in_left = old->in_left;
 539                 node->in_parent = old->in_parent;
 540
 541                 if (old->in_parent) {
 542                         if (node_is_left_child(old))
 543                                 old->in_parent->in_left = node;
 544                         else
 545                                 old->in_parent->in_right = node;
 546                 } else {
 547                         *root = node;
 548                 }
 549
 550                 old->in_left->in_parent = node;
 551                 if (old->in_right)
 552                         old->in_right->in_parent = node;
 553                 update_maxhigh(child, node->in_max_high);
 554                 update_maxhigh(node, old->in_max_high);
 555                 goto color;
 556         }
 557         parent = node->in_parent;
 558         color = node->in_color;
 559
 560         if (child)
 561                 child->in_parent = parent;
 562         if (parent) {
 563                 if (node_is_left_child(node))
 564                         parent->in_left = child;
 565                 else
 566                         parent->in_right = child;
 567         } else {
 568                 *root = child;
 569         }
 570
 571         update_maxhigh(child, node->in_max_high);
 572
 573 color:
 574         if (color == INTERVAL_BLACK)
 575                 interval_erase_color(child, parent, root);
 576         EXIT;
 577 }
 578 EXPORT_SYMBOL(interval_erase);
 579
 580 static inline int interval_may_overlap(struct interval_node *node,
 581                                           struct interval_node_extent *ext)
 582 {
 583         return (ext->start <= node->in_max_high &&
 584                 ext->end >= interval_low(node));
 585 }
 586
 587 /*
 588  * This function finds all intervals that overlap interval ext,
 589  * and calls func to handle resulted intervals one by one.
 590  * in lustre, this function will find all conflicting locks in
 591  * the granted queue and add these locks to the ast work list.
 592  *
 593  * {
 594  *       if (node == NULL)
 595  *               return 0;
 596  *       if (ext->end < interval_low(node)) {
 597  *               interval_search(node->in_left, ext, func, data);
 598  *       } else if (interval_may_overlap(node, ext)) {
 599  *               if (extent_overlapped(ext, &node->in_extent))
 600  *                       func(node, data);
 601  *               interval_search(node->in_left, ext, func, data);
 602  *               interval_search(node->in_right, ext, func, data);
 603  *       }
 604  *       return 0;
 605  * }
 606  *
 607  */
 608 enum interval_iter interval_search(struct interval_node *node,
 609                                    struct interval_node_extent *ext,
 610                                    interval_callback_t func,
 611                                    void *data)
 612 {
 613         struct interval_node *parent;
 614         enum interval_iter rc = INTERVAL_ITER_CONT;
 615
 616         LASSERT(ext != NULL);
 617         LASSERT(func != NULL);
 618
 619         while (node) {
 620                 if (ext->end < interval_low(node)) {
 621                         if (node->in_left) {
 622                                 node = node->in_left;
 623                                 continue;
 624                         }
 625                 } else if (interval_may_overlap(node, ext)) {
 626                         if (extent_overlapped(ext, &node->in_extent)) {
 627                                 rc = func(node, data);
 628                                 if (rc == INTERVAL_ITER_STOP)
 629                                         break;
 630                         }
 631
 632                         if (node->in_left) {
 633                                 node = node->in_left;
 634                                 continue;
 635                         }
 636                         if (node->in_right) {
 637                                 node = node->in_right;
 638                                 continue;
 639                         }
 640                 }
 641
 642                 parent = node->in_parent;
 643                 while (parent) {
 644                         if (node_is_left_child(node) &&
 645                             parent->in_right) {
 646                                 /* If we ever got the left, it means that the
 647                                  * parent met ext->end<interval_low(parent), or
 648                                  * may_overlap(parent). If the former is true,
 649                                  * we needn't go back. So stop early and check
 650                                  * may_overlap(parent) after this loop.  */
 651                                 node = parent->in_right;
 652                                 break;
 653                         }
 654                         node = parent;
 655                         parent = parent->in_parent;
 656                 }
 657                 if (parent == NULL || !interval_may_overlap(parent, ext))
 658                         break;
 659         }
 660
 661         return rc;
 662 }
 663 EXPORT_SYMBOL(interval_search);
 664
 665 static enum interval_iter interval_overlap_cb(struct interval_node *n,
 666                                               void *args)
 667 {
 668         *(int *)args = 1;
 669         return INTERVAL_ITER_STOP;
 670 }
 671
 672 int interval_is_overlapped(struct interval_node *root,
 673                            struct interval_node_extent *ext)
 674 {
 675         int has = 0;
 676         (void)interval_search(root, ext, interval_overlap_cb, &has);
 677         return has;
 678 }
 679 EXPORT_SYMBOL(interval_is_overlapped);
 680
 681 /* Don't expand to low. Expanding downwards is expensive, and meaningless to
 682  * some extents, because programs seldom do IO backward.
 683  *
 684  * The recursive algorithm of expanding low:
 685  * expand_low {
 686  *        struct interval_node *tmp;
 687  *        static __u64 res = 0;
 688  *
 689  *        if (root == NULL)
 690  *                return res;
 691  *        if (root->in_max_high < low) {
 692  *                res = max_u64(root->in_max_high + 1, res);
 693  *                return res;
 694  *        } else if (low < interval_low(root)) {
 695  *                interval_expand_low(root->in_left, low);
 696  *                return res;
 697  *        }
 698  *
 699  *        if (interval_high(root) < low)
 700  *                res = max_u64(interval_high(root) + 1, res);
 701  *        interval_expand_low(root->in_left, low);
 702  *        interval_expand_low(root->in_right, low);
 703  *
 704  *        return res;
 705  * }
 706  *
 707  * It's much easy to eliminate the recursion, see interval_search for
 708  * an example. -jay
 709  */
 710 static inline __u64 interval_expand_low(struct interval_node *root, __u64 low)
 711 {
 712         /* we only concern the empty tree right now. */
 713         if (root == NULL)
 714                 return 0;
 715         return low;
 716 }
 717
 718 static inline __u64 interval_expand_high(struct interval_node *node, __u64 high)
 719 {
 720         __u64 result = ~0;
 721
 722         while (node != NULL) {
 723                 if (node->in_max_high < high)
 724                         break;
 725
 726                 if (interval_low(node) > high) {
 727                         result = interval_low(node) - 1;
 728                         node = node->in_left;
 729                 } else {
 730                         node = node->in_right;
 731                 }
 732         }
 733
 734         return result;
 735 }
 736
 737 /* expanding the extent based on @ext. */
 738 void interval_expand(struct interval_node *root,
 739                      struct interval_node_extent *ext,
 740                      struct interval_node_extent *limiter)
 741 {
 742         /* The assertion of interval_is_overlapped is expensive because we may
 743          * travel many nodes to find the overlapped node. */
 744         LASSERT(interval_is_overlapped(root, ext) == 0);
 745         if (!limiter || limiter->start < ext->start)
 746                 ext->start = interval_expand_low(root, ext->start);
 747         if (!limiter || limiter->end > ext->end)
 748                 ext->end = interval_expand_high(root, ext->end);
 749         LASSERT(interval_is_overlapped(root, ext) == 0);
 750 }
 751 EXPORT_SYMBOL(interval_expand);