1 /*
   2  * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "gc/parallel/cardTableExtension.hpp"
  27 #include "gc/parallel/gcTaskManager.hpp"
  28 #include "gc/parallel/objectStartArray.inline.hpp"
  29 #include "gc/parallel/parallelScavengeHeap.hpp"
  30 #include "gc/parallel/psPromotionManager.inline.hpp"
  31 #include "gc/parallel/psScavenge.hpp"
  32 #include "gc/parallel/psTasks.hpp"
  33 #include "gc/parallel/psYoungGen.hpp"
  34 #include "oops/oop.inline.hpp"
  35 #include "runtime/prefetch.inline.hpp"
  36 #include "utilities/align.hpp"
  37 
  38 // Checks an individual oop for missing precise marks. Mark
  39 // may be either dirty or newgen.
  40 class CheckForUnmarkedOops : public OopClosure {
  41  private:
  42   PSYoungGen*         _young_gen;
  43   CardTableExtension* _card_table;
  44   HeapWord*           _unmarked_addr;
  45 
  46  protected:
  47   template <class T> void do_oop_work(T* p) {
  48     oop obj = oopDesc::load_decode_heap_oop(p);
  49     if (_young_gen->is_in_reserved(obj) &&
  50         !_card_table->addr_is_marked_imprecise(p)) {
  51       // Don't overwrite the first missing card mark
  52       if (_unmarked_addr == NULL) {
  53         _unmarked_addr = (HeapWord*)p;
  54       }
  55     }
  56   }
  57 
  58  public:
  59   CheckForUnmarkedOops(PSYoungGen* young_gen, CardTableExtension* card_table) :
  60     _young_gen(young_gen), _card_table(card_table), _unmarked_addr(NULL) { }
  61 
  62   virtual void do_oop(oop* p)       { CheckForUnmarkedOops::do_oop_work(p); }
  63   virtual void do_oop(narrowOop* p) { CheckForUnmarkedOops::do_oop_work(p); }
  64 
  65   bool has_unmarked_oop() {
  66     return _unmarked_addr != NULL;
  67   }
  68 };
  69 
  70 // Checks all objects for the existence of some type of mark,
  71 // precise or imprecise, dirty or newgen.
  72 class CheckForUnmarkedObjects : public ObjectClosure {
  73  private:
  74   PSYoungGen*         _young_gen;
  75   CardTableExtension* _card_table;
  76 
  77  public:
  78   CheckForUnmarkedObjects() {
  79     ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
  80     _young_gen = heap->young_gen();
  81     _card_table = barrier_set_cast<CardTableExtension>(heap->barrier_set());
  82     // No point in asserting barrier set type here. Need to make CardTableExtension
  83     // a unique barrier set type.
  84   }
  85 
  86   // Card marks are not precise. The current system can leave us with
  87   // a mismatch of precise marks and beginning of object marks. This means
  88   // we test for missing precise marks first. If any are found, we don't
  89   // fail unless the object head is also unmarked.
  90   virtual void do_object(oop obj) {
  91     CheckForUnmarkedOops object_check(_young_gen, _card_table);
  92     obj->oop_iterate_no_header(&object_check);
  93     if (object_check.has_unmarked_oop()) {
  94       guarantee(_card_table->addr_is_marked_imprecise(obj), "Found unmarked young_gen object");
  95     }
  96   }
  97 };
  98 
  99 // Checks for precise marking of oops as newgen.
 100 class CheckForPreciseMarks : public OopClosure {
 101  private:
 102   PSYoungGen*         _young_gen;
 103   CardTableExtension* _card_table;
 104 
 105  protected:
 106   template <class T> void do_oop_work(T* p) {
 107     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 108     if (_young_gen->is_in_reserved(obj)) {
 109       assert(_card_table->addr_is_marked_precise(p), "Found unmarked precise oop");
 110       _card_table->set_card_newgen(p);
 111     }
 112   }
 113 
 114  public:
 115   CheckForPreciseMarks( PSYoungGen* young_gen, CardTableExtension* card_table ) :
 116     _young_gen(young_gen), _card_table(card_table) { }
 117 
 118   virtual void do_oop(oop* p)       { CheckForPreciseMarks::do_oop_work(p); }
 119   virtual void do_oop(narrowOop* p) { CheckForPreciseMarks::do_oop_work(p); }
 120 };
 121 
 122 // We get passed the space_top value to prevent us from traversing into
 123 // the old_gen promotion labs, which cannot be safely parsed.
 124 
 125 // Do not call this method if the space is empty.
 126 // It is a waste to start tasks and get here only to
 127 // do no work.  If this method needs to be called
 128 // when the space is empty, fix the calculation of
 129 // end_card to allow sp_top == sp->bottom().
 130 
 131 void CardTableExtension::scavenge_contents_parallel(ObjectStartArray* start_array,
 132                                                     MutableSpace* sp,
 133                                                     HeapWord* space_top,
 134                                                     PSPromotionManager* pm,
 135                                                     uint stripe_number,
 136                                                     uint stripe_total) {
 137   int ssize = 128; // Naked constant!  Work unit = 64k.
 138   int dirty_card_count = 0;
 139 
 140   // It is a waste to get here if empty.
 141   assert(sp->bottom() < sp->top(), "Should not be called if empty");
 142   oop* sp_top = (oop*)space_top;
 143   jbyte* start_card = byte_for(sp->bottom());
 144   jbyte* end_card   = byte_for(sp_top - 1) + 1;
 145   oop* last_scanned = NULL; // Prevent scanning objects more than once
 146   // The width of the stripe ssize*stripe_total must be
 147   // consistent with the number of stripes so that the complete slice
 148   // is covered.
 149   size_t slice_width = ssize * stripe_total;
 150   for (jbyte* slice = start_card; slice < end_card; slice += slice_width) {
 151     jbyte* worker_start_card = slice + stripe_number * ssize;
 152     if (worker_start_card >= end_card)
 153       return; // We're done.
 154 
 155     jbyte* worker_end_card = worker_start_card + ssize;
 156     if (worker_end_card > end_card)
 157       worker_end_card = end_card;
 158 
 159     // We do not want to scan objects more than once. In order to accomplish
 160     // this, we assert that any object with an object head inside our 'slice'
 161     // belongs to us. We may need to extend the range of scanned cards if the
 162     // last object continues into the next 'slice'.
 163     //
 164     // Note! ending cards are exclusive!
 165     HeapWord* slice_start = addr_for(worker_start_card);
 166     HeapWord* slice_end = MIN2((HeapWord*) sp_top, addr_for(worker_end_card));
 167 
 168 #ifdef ASSERT
 169     if (GCWorkerDelayMillis > 0) {
 170       // Delay 1 worker so that it proceeds after all the work
 171       // has been completed.
 172       if (stripe_number < 2) {
 173         os::sleep(Thread::current(), GCWorkerDelayMillis, false);
 174       }
 175     }
 176 #endif
 177 
 178     // If there are not objects starting within the chunk, skip it.
 179     if (!start_array->object_starts_in_range(slice_start, slice_end)) {
 180       continue;
 181     }
 182     // Update our beginning addr
 183     HeapWord* first_object = start_array->object_start(slice_start);
 184     debug_only(oop* first_object_within_slice = (oop*) first_object;)
 185     if (first_object < slice_start) {
 186       last_scanned = (oop*)(first_object + oop(first_object)->size());
 187       debug_only(first_object_within_slice = last_scanned;)
 188       worker_start_card = byte_for(last_scanned);
 189     }
 190 
 191     // Update the ending addr
 192     if (slice_end < (HeapWord*)sp_top) {
 193       // The subtraction is important! An object may start precisely at slice_end.
 194       HeapWord* last_object = start_array->object_start(slice_end - 1);
 195       slice_end = last_object + oop(last_object)->size();
 196       // worker_end_card is exclusive, so bump it one past the end of last_object's
 197       // covered span.
 198       worker_end_card = byte_for(slice_end) + 1;
 199 
 200       if (worker_end_card > end_card)
 201         worker_end_card = end_card;
 202     }
 203 
 204     assert(slice_end <= (HeapWord*)sp_top, "Last object in slice crosses space boundary");
 205     assert(is_valid_card_address(worker_start_card), "Invalid worker start card");
 206     assert(is_valid_card_address(worker_end_card), "Invalid worker end card");
 207     // Note that worker_start_card >= worker_end_card is legal, and happens when
 208     // an object spans an entire slice.
 209     assert(worker_start_card <= end_card, "worker start card beyond end card");
 210     assert(worker_end_card <= end_card, "worker end card beyond end card");
 211 
 212     jbyte* current_card = worker_start_card;
 213     while (current_card < worker_end_card) {
 214       // Find an unclean card.
 215       while (current_card < worker_end_card && card_is_clean(*current_card)) {
 216         current_card++;
 217       }
 218       jbyte* first_unclean_card = current_card;
 219 
 220       // Find the end of a run of contiguous unclean cards
 221       while (current_card < worker_end_card && !card_is_clean(*current_card)) {
 222         while (current_card < worker_end_card && !card_is_clean(*current_card)) {
 223           current_card++;
 224         }
 225 
 226         if (current_card < worker_end_card) {
 227           // Some objects may be large enough to span several cards. If such
 228           // an object has more than one dirty card, separated by a clean card,
 229           // we will attempt to scan it twice. The test against "last_scanned"
 230           // prevents the redundant object scan, but it does not prevent newly
 231           // marked cards from being cleaned.
 232           HeapWord* last_object_in_dirty_region = start_array->object_start(addr_for(current_card)-1);
 233           size_t size_of_last_object = oop(last_object_in_dirty_region)->size();
 234           HeapWord* end_of_last_object = last_object_in_dirty_region + size_of_last_object;
 235           jbyte* ending_card_of_last_object = byte_for(end_of_last_object);
 236           assert(ending_card_of_last_object <= worker_end_card, "ending_card_of_last_object is greater than worker_end_card");
 237           if (ending_card_of_last_object > current_card) {
 238             // This means the object spans the next complete card.
 239             // We need to bump the current_card to ending_card_of_last_object
 240             current_card = ending_card_of_last_object;
 241           }
 242         }
 243       }
 244       jbyte* following_clean_card = current_card;
 245 
 246       if (first_unclean_card < worker_end_card) {
 247         oop* p = (oop*) start_array->object_start(addr_for(first_unclean_card));
 248         assert((HeapWord*)p <= addr_for(first_unclean_card), "checking");
 249         // "p" should always be >= "last_scanned" because newly GC dirtied
 250         // cards are no longer scanned again (see comment at end
 251         // of loop on the increment of "current_card").  Test that
 252         // hypothesis before removing this code.
 253         // If this code is removed, deal with the first time through
 254         // the loop when the last_scanned is the object starting in
 255         // the previous slice.
 256         assert((p >= last_scanned) ||
 257                (last_scanned == first_object_within_slice),
 258                "Should no longer be possible");
 259         if (p < last_scanned) {
 260           // Avoid scanning more than once; this can happen because
 261           // newgen cards set by GC may a different set than the
 262           // originally dirty set
 263           p = last_scanned;
 264         }
 265         oop* to = (oop*)addr_for(following_clean_card);
 266 
 267         // Test slice_end first!
 268         if ((HeapWord*)to > slice_end) {
 269           to = (oop*)slice_end;
 270         } else if (to > sp_top) {
 271           to = sp_top;
 272         }
 273 
 274         // we know which cards to scan, now clear them
 275         if (first_unclean_card <= worker_start_card+1)
 276           first_unclean_card = worker_start_card+1;
 277         if (following_clean_card >= worker_end_card-1)
 278           following_clean_card = worker_end_card-1;
 279 
 280         while (first_unclean_card < following_clean_card) {
 281           *first_unclean_card++ = clean_card;
 282         }
 283 
 284         const int interval = PrefetchScanIntervalInBytes;
 285         // scan all objects in the range
 286         if (interval != 0) {
 287           while (p < to) {
 288             Prefetch::write(p, interval);
 289             oop m = oop(p);
 290             assert(oopDesc::is_oop_or_null(m), "Expected an oop or NULL for header field at " PTR_FORMAT, p2i(m));
 291             pm->push_contents(m);
 292             p += m->size();
 293           }
 294           pm->drain_stacks_cond_depth();
 295         } else {
 296           while (p < to) {
 297             oop m = oop(p);
 298             assert(oopDesc::is_oop_or_null(m), "Expected an oop or NULL for header field at " PTR_FORMAT, p2i(m));
 299             pm->push_contents(m);
 300             p += m->size();
 301           }
 302           pm->drain_stacks_cond_depth();
 303         }
 304         last_scanned = p;
 305       }
 306       // "current_card" is still the "following_clean_card" or
 307       // the current_card is >= the worker_end_card so the
 308       // loop will not execute again.
 309       assert((current_card == following_clean_card) ||
 310              (current_card >= worker_end_card),
 311         "current_card should only be incremented if it still equals "
 312         "following_clean_card");
 313       // Increment current_card so that it is not processed again.
 314       // It may now be dirty because a old-to-young pointer was
 315       // found on it an updated.  If it is now dirty, it cannot be
 316       // be safely cleaned in the next iteration.
 317       current_card++;
 318     }
 319   }
 320 }
 321 
 322 // This should be called before a scavenge.
 323 void CardTableExtension::verify_all_young_refs_imprecise() {
 324   CheckForUnmarkedObjects check;
 325 
 326   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 327   PSOldGen* old_gen = heap->old_gen();
 328 
 329   old_gen->object_iterate(&check);
 330 }
 331 
 332 // This should be called immediately after a scavenge, before mutators resume.
 333 void CardTableExtension::verify_all_young_refs_precise() {
 334   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 335   PSOldGen* old_gen = heap->old_gen();
 336 
 337   CheckForPreciseMarks check(
 338     heap->young_gen(),
 339     barrier_set_cast<CardTableExtension>(heap->barrier_set()));
 340 
 341   old_gen->oop_iterate_no_header(&check);
 342 
 343   verify_all_young_refs_precise_helper(old_gen->object_space()->used_region());
 344 }
 345 
 346 void CardTableExtension::verify_all_young_refs_precise_helper(MemRegion mr) {
 347   CardTableExtension* card_table =
 348     barrier_set_cast<CardTableExtension>(ParallelScavengeHeap::heap()->barrier_set());
 349 
 350   jbyte* bot = card_table->byte_for(mr.start());
 351   jbyte* top = card_table->byte_for(mr.end());
 352   while(bot <= top) {
 353     assert(*bot == clean_card || *bot == verify_card, "Found unwanted or unknown card mark");
 354     if (*bot == verify_card)
 355       *bot = youngergen_card;
 356     bot++;
 357   }
 358 }
 359 
 360 bool CardTableExtension::addr_is_marked_imprecise(void *addr) {
 361   jbyte* p = byte_for(addr);
 362   jbyte val = *p;
 363 
 364   if (card_is_dirty(val))
 365     return true;
 366 
 367   if (card_is_newgen(val))
 368     return true;
 369 
 370   if (card_is_clean(val))
 371     return false;
 372 
 373   assert(false, "Found unhandled card mark type");
 374 
 375   return false;
 376 }
 377 
 378 // Also includes verify_card
 379 bool CardTableExtension::addr_is_marked_precise(void *addr) {
 380   jbyte* p = byte_for(addr);
 381   jbyte val = *p;
 382 
 383   if (card_is_newgen(val))
 384     return true;
 385 
 386   if (card_is_verify(val))
 387     return true;
 388 
 389   if (card_is_clean(val))
 390     return false;
 391 
 392   if (card_is_dirty(val))
 393     return false;
 394 
 395   assert(false, "Found unhandled card mark type");
 396 
 397   return false;
 398 }
 399 
 400 // Assumes that only the base or the end changes.  This allows indentification
 401 // of the region that is being resized.  The
 402 // CardTableModRefBS::resize_covered_region() is used for the normal case
 403 // where the covered regions are growing or shrinking at the high end.
 404 // The method resize_covered_region_by_end() is analogous to
 405 // CardTableModRefBS::resize_covered_region() but
 406 // for regions that grow or shrink at the low end.
 407 void CardTableExtension::resize_covered_region(MemRegion new_region) {
 408 
 409   for (int i = 0; i < _cur_covered_regions; i++) {
 410     if (_covered[i].start() == new_region.start()) {
 411       // Found a covered region with the same start as the
 412       // new region.  The region is growing or shrinking
 413       // from the start of the region.
 414       resize_covered_region_by_start(new_region);
 415       return;
 416     }
 417     if (_covered[i].start() > new_region.start()) {
 418       break;
 419     }
 420   }
 421 
 422   int changed_region = -1;
 423   for (int j = 0; j < _cur_covered_regions; j++) {
 424     if (_covered[j].end() == new_region.end()) {
 425       changed_region = j;
 426       // This is a case where the covered region is growing or shrinking
 427       // at the start of the region.
 428       assert(changed_region != -1, "Don't expect to add a covered region");
 429       assert(_covered[changed_region].byte_size() != new_region.byte_size(),
 430         "The sizes should be different here");
 431       resize_covered_region_by_end(changed_region, new_region);
 432       return;
 433     }
 434   }
 435   // This should only be a new covered region (where no existing
 436   // covered region matches at the start or the end).
 437   assert(_cur_covered_regions < _max_covered_regions,
 438     "An existing region should have been found");
 439   resize_covered_region_by_start(new_region);
 440 }
 441 
 442 void CardTableExtension::resize_covered_region_by_start(MemRegion new_region) {
 443   CardTableModRefBS::resize_covered_region(new_region);
 444   debug_only(verify_guard();)
 445 }
 446 
 447 void CardTableExtension::resize_covered_region_by_end(int changed_region,
 448                                                       MemRegion new_region) {
 449   assert(SafepointSynchronize::is_at_safepoint(),
 450     "Only expect an expansion at the low end at a GC");
 451   debug_only(verify_guard();)
 452 #ifdef ASSERT
 453   for (int k = 0; k < _cur_covered_regions; k++) {
 454     if (_covered[k].end() == new_region.end()) {
 455       assert(changed_region == k, "Changed region is incorrect");
 456       break;
 457     }
 458   }
 459 #endif
 460 
 461   // Commit new or uncommit old pages, if necessary.
 462   if (resize_commit_uncommit(changed_region, new_region)) {
 463     // Set the new start of the committed region
 464     resize_update_committed_table(changed_region, new_region);
 465   }
 466 
 467   // Update card table entries
 468   resize_update_card_table_entries(changed_region, new_region);
 469 
 470   // Update the covered region
 471   resize_update_covered_table(changed_region, new_region);
 472 
 473   int ind = changed_region;
 474   log_trace(gc, barrier)("CardTableModRefBS::resize_covered_region: ");
 475   log_trace(gc, barrier)("    _covered[%d].start(): " INTPTR_FORMAT "  _covered[%d].last(): " INTPTR_FORMAT,
 476                 ind, p2i(_covered[ind].start()), ind, p2i(_covered[ind].last()));
 477   log_trace(gc, barrier)("    _committed[%d].start(): " INTPTR_FORMAT "  _committed[%d].last(): " INTPTR_FORMAT,
 478                 ind, p2i(_committed[ind].start()), ind, p2i(_committed[ind].last()));
 479   log_trace(gc, barrier)("    byte_for(start): " INTPTR_FORMAT "  byte_for(last): " INTPTR_FORMAT,
 480                 p2i(byte_for(_covered[ind].start())),  p2i(byte_for(_covered[ind].last())));
 481   log_trace(gc, barrier)("    addr_for(start): " INTPTR_FORMAT "  addr_for(last): " INTPTR_FORMAT,
 482                 p2i(addr_for((jbyte*) _committed[ind].start())), p2i(addr_for((jbyte*) _committed[ind].last())));
 483 
 484   debug_only(verify_guard();)
 485 }
 486 
 487 bool CardTableExtension::resize_commit_uncommit(int changed_region,
 488                                                 MemRegion new_region) {
 489   bool result = false;
 490   // Commit new or uncommit old pages, if necessary.
 491   MemRegion cur_committed = _committed[changed_region];
 492   assert(_covered[changed_region].end() == new_region.end(),
 493     "The ends of the regions are expected to match");
 494   // Extend the start of this _committed region to
 495   // to cover the start of any previous _committed region.
 496   // This forms overlapping regions, but never interior regions.
 497   HeapWord* min_prev_start = lowest_prev_committed_start(changed_region);
 498   if (min_prev_start < cur_committed.start()) {
 499     // Only really need to set start of "cur_committed" to
 500     // the new start (min_prev_start) but assertion checking code
 501     // below use cur_committed.end() so make it correct.
 502     MemRegion new_committed =
 503         MemRegion(min_prev_start, cur_committed.end());
 504     cur_committed = new_committed;
 505   }
 506 #ifdef ASSERT
 507   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 508   assert(cur_committed.start() == align_up(cur_committed.start(), os::vm_page_size()),
 509     "Starts should have proper alignment");
 510 #endif
 511 
 512   jbyte* new_start = byte_for(new_region.start());
 513   // Round down because this is for the start address
 514   HeapWord* new_start_aligned =
 515     (HeapWord*)align_down((uintptr_t)new_start, os::vm_page_size());
 516   // The guard page is always committed and should not be committed over.
 517   // This method is used in cases where the generation is growing toward
 518   // lower addresses but the guard region is still at the end of the
 519   // card table.  That still makes sense when looking for writes
 520   // off the end of the card table.
 521   if (new_start_aligned < cur_committed.start()) {
 522     // Expand the committed region
 523     //
 524     // Case A
 525     //                                          |+ guard +|
 526     //                          |+ cur committed +++++++++|
 527     //                  |+ new committed +++++++++++++++++|
 528     //
 529     // Case B
 530     //                                          |+ guard +|
 531     //                        |+ cur committed +|
 532     //                  |+ new committed +++++++|
 533     //
 534     // These are not expected because the calculation of the
 535     // cur committed region and the new committed region
 536     // share the same end for the covered region.
 537     // Case C
 538     //                                          |+ guard +|
 539     //                        |+ cur committed +|
 540     //                  |+ new committed +++++++++++++++++|
 541     // Case D
 542     //                                          |+ guard +|
 543     //                        |+ cur committed +++++++++++|
 544     //                  |+ new committed +++++++|
 545 
 546     HeapWord* new_end_for_commit =
 547       MIN2(cur_committed.end(), _guard_region.start());
 548     if(new_start_aligned < new_end_for_commit) {
 549       MemRegion new_committed =
 550         MemRegion(new_start_aligned, new_end_for_commit);
 551       os::commit_memory_or_exit((char*)new_committed.start(),
 552                                 new_committed.byte_size(), !ExecMem,
 553                                 "card table expansion");
 554     }
 555     result = true;
 556   } else if (new_start_aligned > cur_committed.start()) {
 557     // Shrink the committed region
 558 #if 0 // uncommitting space is currently unsafe because of the interactions
 559       // of growing and shrinking regions.  One region A can uncommit space
 560       // that it owns but which is being used by another region B (maybe).
 561       // Region B has not committed the space because it was already
 562       // committed by region A.
 563     MemRegion uncommit_region = committed_unique_to_self(changed_region,
 564       MemRegion(cur_committed.start(), new_start_aligned));
 565     if (!uncommit_region.is_empty()) {
 566       if (!os::uncommit_memory((char*)uncommit_region.start(),
 567                                uncommit_region.byte_size())) {
 568         // If the uncommit fails, ignore it.  Let the
 569         // committed table resizing go even though the committed
 570         // table will over state the committed space.
 571       }
 572     }
 573 #else
 574     assert(!result, "Should be false with current workaround");
 575 #endif
 576   }
 577   assert(_committed[changed_region].end() == cur_committed.end(),
 578     "end should not change");
 579   return result;
 580 }
 581 
 582 void CardTableExtension::resize_update_committed_table(int changed_region,
 583                                                        MemRegion new_region) {
 584 
 585   jbyte* new_start = byte_for(new_region.start());
 586   // Set the new start of the committed region
 587   HeapWord* new_start_aligned =
 588     (HeapWord*)align_down(new_start, os::vm_page_size());
 589   MemRegion new_committed = MemRegion(new_start_aligned,
 590     _committed[changed_region].end());
 591   _committed[changed_region] = new_committed;
 592   _committed[changed_region].set_start(new_start_aligned);
 593 }
 594 
 595 void CardTableExtension::resize_update_card_table_entries(int changed_region,
 596                                                           MemRegion new_region) {
 597   debug_only(verify_guard();)
 598   MemRegion original_covered = _covered[changed_region];
 599   // Initialize the card entries.  Only consider the
 600   // region covered by the card table (_whole_heap)
 601   jbyte* entry;
 602   if (new_region.start() < _whole_heap.start()) {
 603     entry = byte_for(_whole_heap.start());
 604   } else {
 605     entry = byte_for(new_region.start());
 606   }
 607   jbyte* end = byte_for(original_covered.start());
 608   // If _whole_heap starts at the original covered regions start,
 609   // this loop will not execute.
 610   while (entry < end) { *entry++ = clean_card; }
 611 }
 612 
 613 void CardTableExtension::resize_update_covered_table(int changed_region,
 614                                                      MemRegion new_region) {
 615   // Update the covered region
 616   _covered[changed_region].set_start(new_region.start());
 617   _covered[changed_region].set_word_size(new_region.word_size());
 618 
 619   // reorder regions.  There should only be at most 1 out
 620   // of order.
 621   for (int i = _cur_covered_regions-1 ; i > 0; i--) {
 622     if (_covered[i].start() < _covered[i-1].start()) {
 623         MemRegion covered_mr = _covered[i-1];
 624         _covered[i-1] = _covered[i];
 625         _covered[i] = covered_mr;
 626         MemRegion committed_mr = _committed[i-1];
 627       _committed[i-1] = _committed[i];
 628       _committed[i] = committed_mr;
 629       break;
 630     }
 631   }
 632 #ifdef ASSERT
 633   for (int m = 0; m < _cur_covered_regions-1; m++) {
 634     assert(_covered[m].start() <= _covered[m+1].start(),
 635       "Covered regions out of order");
 636     assert(_committed[m].start() <= _committed[m+1].start(),
 637       "Committed regions out of order");
 638   }
 639 #endif
 640 }
 641 
 642 // Returns the start of any committed region that is lower than
 643 // the target committed region (index ind) and that intersects the
 644 // target region.  If none, return start of target region.
 645 //
 646 //      -------------
 647 //      |           |
 648 //      -------------
 649 //              ------------
 650 //              | target   |
 651 //              ------------
 652 //                               -------------
 653 //                               |           |
 654 //                               -------------
 655 //      ^ returns this
 656 //
 657 //      -------------
 658 //      |           |
 659 //      -------------
 660 //                      ------------
 661 //                      | target   |
 662 //                      ------------
 663 //                               -------------
 664 //                               |           |
 665 //                               -------------
 666 //                      ^ returns this
 667 
 668 HeapWord* CardTableExtension::lowest_prev_committed_start(int ind) const {
 669   assert(_cur_covered_regions >= 0, "Expecting at least on region");
 670   HeapWord* min_start = _committed[ind].start();
 671   for (int j = 0; j < ind; j++) {
 672     HeapWord* this_start = _committed[j].start();
 673     if ((this_start < min_start) &&
 674         !(_committed[j].intersection(_committed[ind])).is_empty()) {
 675        min_start = this_start;
 676     }
 677   }
 678   return min_start;
 679 }