1 /*
   2  * Copyright (c) 2001, 2018, 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/gcTaskManager.hpp"
  27 #include "gc/parallel/objectStartArray.inline.hpp"
  28 #include "gc/parallel/parallelScavengeHeap.inline.hpp"
  29 #include "gc/parallel/psCardTable.hpp"
  30 #include "gc/parallel/psPromotionManager.inline.hpp"
  31 #include "gc/parallel/psScavenge.inline.hpp"
  32 #include "gc/parallel/psTasks.hpp"
  33 #include "gc/parallel/psYoungGen.hpp"
  34 #include "memory/iterator.inline.hpp"
  35 #include "oops/access.inline.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "runtime/prefetch.inline.hpp"
  38 #include "utilities/align.hpp"
  39 
  40 // Checks an individual oop for missing precise marks. Mark
  41 // may be either dirty or newgen.
  42 class CheckForUnmarkedOops : public BasicOopIterateClosure {
  43  private:
  44   PSYoungGen*  _young_gen;
  45   PSCardTable* _card_table;
  46   HeapWord*    _unmarked_addr;
  47 
  48  protected:
  49   template <class T> void do_oop_work(T* p) {
  50     oop obj = RawAccess<>::oop_load(p);
  51     if (_young_gen->is_in_reserved(obj) &&
  52         !_card_table->addr_is_marked_imprecise(p)) {
  53       // Don't overwrite the first missing card mark
  54       if (_unmarked_addr == NULL) {
  55         _unmarked_addr = (HeapWord*)p;
  56       }
  57     }
  58   }
  59 
  60  public:
  61   CheckForUnmarkedOops(PSYoungGen* young_gen, PSCardTable* card_table) :
  62     _young_gen(young_gen), _card_table(card_table), _unmarked_addr(NULL) { }
  63 
  64   virtual void do_oop(oop* p)       { CheckForUnmarkedOops::do_oop_work(p); }
  65   virtual void do_oop(narrowOop* p) { CheckForUnmarkedOops::do_oop_work(p); }
  66 
  67   bool has_unmarked_oop() {
  68     return _unmarked_addr != NULL;
  69   }
  70 };
  71 
  72 // Checks all objects for the existence of some type of mark,
  73 // precise or imprecise, dirty or newgen.
  74 class CheckForUnmarkedObjects : public ObjectClosure {
  75  private:
  76   PSYoungGen*  _young_gen;
  77   PSCardTable* _card_table;
  78 
  79  public:
  80   CheckForUnmarkedObjects() {
  81     ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
  82     _young_gen = heap->young_gen();
  83     _card_table = heap->card_table();
  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(&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 BasicOopIterateClosure {
 101  private:
 102   PSYoungGen*  _young_gen;
 103   PSCardTable* _card_table;
 104 
 105  protected:
 106   template <class T> void do_oop_work(T* p) {
 107     oop obj = RawAccess<IS_NOT_NULL>::oop_load(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, PSCardTable* 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 PSCardTable::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   CardValue* start_card = byte_for(sp->bottom());
 144   CardValue* 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 (CardValue* slice = start_card; slice < end_card; slice += slice_width) {
 151     CardValue* worker_start_card = slice + stripe_number * ssize;
 152     if (worker_start_card >= end_card)
 153       return; // We're done.
 154 
 155     CardValue* 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     CardValue* 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       CardValue* 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           CardValue* 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       CardValue* 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 PSCardTable::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 PSCardTable::verify_all_young_refs_precise() {
 334   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 335   PSOldGen* old_gen = heap->old_gen();
 336 
 337   CheckForPreciseMarks check(heap->young_gen(), this);
 338 
 339   old_gen->oop_iterate(&check);
 340 
 341   verify_all_young_refs_precise_helper(old_gen->object_space()->used_region());
 342 }
 343 
 344 void PSCardTable::verify_all_young_refs_precise_helper(MemRegion mr) {
 345   CardValue* bot = byte_for(mr.start());
 346   CardValue* top = byte_for(mr.end());
 347   while (bot <= top) {
 348     assert(*bot == clean_card || *bot == verify_card, "Found unwanted or unknown card mark");
 349     if (*bot == verify_card)
 350       *bot = youngergen_card;
 351     bot++;
 352   }
 353 }
 354 
 355 bool PSCardTable::addr_is_marked_imprecise(void *addr) {
 356   CardValue* p = byte_for(addr);
 357   CardValue val = *p;
 358 
 359   if (card_is_dirty(val))
 360     return true;
 361 
 362   if (card_is_newgen(val))
 363     return true;
 364 
 365   if (card_is_clean(val))
 366     return false;
 367 
 368   assert(false, "Found unhandled card mark type");
 369 
 370   return false;
 371 }
 372 
 373 // Also includes verify_card
 374 bool PSCardTable::addr_is_marked_precise(void *addr) {
 375   CardValue* p = byte_for(addr);
 376   CardValue val = *p;
 377 
 378   if (card_is_newgen(val))
 379     return true;
 380 
 381   if (card_is_verify(val))
 382     return true;
 383 
 384   if (card_is_clean(val))
 385     return false;
 386 
 387   if (card_is_dirty(val))
 388     return false;
 389 
 390   assert(false, "Found unhandled card mark type");
 391 
 392   return false;
 393 }
 394 
 395 // Assumes that only the base or the end changes.  This allows indentification
 396 // of the region that is being resized.  The
 397 // CardTable::resize_covered_region() is used for the normal case
 398 // where the covered regions are growing or shrinking at the high end.
 399 // The method resize_covered_region_by_end() is analogous to
 400 // CardTable::resize_covered_region() but
 401 // for regions that grow or shrink at the low end.
 402 void PSCardTable::resize_covered_region(MemRegion new_region) {
 403   for (int i = 0; i < _cur_covered_regions; i++) {
 404     if (_covered[i].start() == new_region.start()) {
 405       // Found a covered region with the same start as the
 406       // new region.  The region is growing or shrinking
 407       // from the start of the region.
 408       resize_covered_region_by_start(new_region);
 409       return;
 410     }
 411     if (_covered[i].start() > new_region.start()) {
 412       break;
 413     }
 414   }
 415 
 416   int changed_region = -1;
 417   for (int j = 0; j < _cur_covered_regions; j++) {
 418     if (_covered[j].end() == new_region.end()) {
 419       changed_region = j;
 420       // This is a case where the covered region is growing or shrinking
 421       // at the start of the region.
 422       assert(changed_region != -1, "Don't expect to add a covered region");
 423       assert(_covered[changed_region].byte_size() != new_region.byte_size(),
 424         "The sizes should be different here");
 425       resize_covered_region_by_end(changed_region, new_region);
 426       return;
 427     }
 428   }
 429   // This should only be a new covered region (where no existing
 430   // covered region matches at the start or the end).
 431   assert(_cur_covered_regions < _max_covered_regions,
 432     "An existing region should have been found");
 433   resize_covered_region_by_start(new_region);
 434 }
 435 
 436 void PSCardTable::resize_covered_region_by_start(MemRegion new_region) {
 437   CardTable::resize_covered_region(new_region);
 438   debug_only(verify_guard();)
 439 }
 440 
 441 void PSCardTable::resize_covered_region_by_end(int changed_region,
 442                                                MemRegion new_region) {
 443   assert(SafepointSynchronize::is_at_safepoint(),
 444     "Only expect an expansion at the low end at a GC");
 445   debug_only(verify_guard();)
 446 #ifdef ASSERT
 447   for (int k = 0; k < _cur_covered_regions; k++) {
 448     if (_covered[k].end() == new_region.end()) {
 449       assert(changed_region == k, "Changed region is incorrect");
 450       break;
 451     }
 452   }
 453 #endif
 454 
 455   // Commit new or uncommit old pages, if necessary.
 456   if (resize_commit_uncommit(changed_region, new_region)) {
 457     // Set the new start of the committed region
 458     resize_update_committed_table(changed_region, new_region);
 459   }
 460 
 461   // Update card table entries
 462   resize_update_card_table_entries(changed_region, new_region);
 463 
 464   // Update the covered region
 465   resize_update_covered_table(changed_region, new_region);
 466 
 467   int ind = changed_region;
 468   log_trace(gc, barrier)("CardTable::resize_covered_region: ");
 469   log_trace(gc, barrier)("    _covered[%d].start(): " INTPTR_FORMAT "  _covered[%d].last(): " INTPTR_FORMAT,
 470                 ind, p2i(_covered[ind].start()), ind, p2i(_covered[ind].last()));
 471   log_trace(gc, barrier)("    _committed[%d].start(): " INTPTR_FORMAT "  _committed[%d].last(): " INTPTR_FORMAT,
 472                 ind, p2i(_committed[ind].start()), ind, p2i(_committed[ind].last()));
 473   log_trace(gc, barrier)("    byte_for(start): " INTPTR_FORMAT "  byte_for(last): " INTPTR_FORMAT,
 474                 p2i(byte_for(_covered[ind].start())),  p2i(byte_for(_covered[ind].last())));
 475   log_trace(gc, barrier)("    addr_for(start): " INTPTR_FORMAT "  addr_for(last): " INTPTR_FORMAT,
 476                 p2i(addr_for((CardValue*) _committed[ind].start())), p2i(addr_for((CardValue*) _committed[ind].last())));
 477 
 478   debug_only(verify_guard();)
 479 }
 480 
 481 bool PSCardTable::resize_commit_uncommit(int changed_region,
 482                                          MemRegion new_region) {
 483   bool result = false;
 484   // Commit new or uncommit old pages, if necessary.
 485   MemRegion cur_committed = _committed[changed_region];
 486   assert(_covered[changed_region].end() == new_region.end(),
 487     "The ends of the regions are expected to match");
 488   // Extend the start of this _committed region to
 489   // to cover the start of any previous _committed region.
 490   // This forms overlapping regions, but never interior regions.
 491   HeapWord* min_prev_start = lowest_prev_committed_start(changed_region);
 492   if (min_prev_start < cur_committed.start()) {
 493     // Only really need to set start of "cur_committed" to
 494     // the new start (min_prev_start) but assertion checking code
 495     // below use cur_committed.end() so make it correct.
 496     MemRegion new_committed =
 497         MemRegion(min_prev_start, cur_committed.end());
 498     cur_committed = new_committed;
 499   }
 500 #ifdef ASSERT
 501   ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
 502   assert(cur_committed.start() == align_up(cur_committed.start(), os::vm_page_size()),
 503          "Starts should have proper alignment");
 504 #endif
 505 
 506   CardValue* new_start = byte_for(new_region.start());
 507   // Round down because this is for the start address
 508   HeapWord* new_start_aligned = align_down((HeapWord*)new_start, os::vm_page_size());
 509   // The guard page is always committed and should not be committed over.
 510   // This method is used in cases where the generation is growing toward
 511   // lower addresses but the guard region is still at the end of the
 512   // card table.  That still makes sense when looking for writes
 513   // off the end of the card table.
 514   if (new_start_aligned < cur_committed.start()) {
 515     // Expand the committed region
 516     //
 517     // Case A
 518     //                                          |+ guard +|
 519     //                          |+ cur committed +++++++++|
 520     //                  |+ new committed +++++++++++++++++|
 521     //
 522     // Case B
 523     //                                          |+ guard +|
 524     //                        |+ cur committed +|
 525     //                  |+ new committed +++++++|
 526     //
 527     // These are not expected because the calculation of the
 528     // cur committed region and the new committed region
 529     // share the same end for the covered region.
 530     // Case C
 531     //                                          |+ guard +|
 532     //                        |+ cur committed +|
 533     //                  |+ new committed +++++++++++++++++|
 534     // Case D
 535     //                                          |+ guard +|
 536     //                        |+ cur committed +++++++++++|
 537     //                  |+ new committed +++++++|
 538 
 539     HeapWord* new_end_for_commit =
 540       MIN2(cur_committed.end(), _guard_region.start());
 541     if(new_start_aligned < new_end_for_commit) {
 542       MemRegion new_committed =
 543         MemRegion(new_start_aligned, new_end_for_commit);
 544       os::commit_memory_or_exit((char*)new_committed.start(),
 545                                 new_committed.byte_size(), !ExecMem,
 546                                 "card table expansion");
 547     }
 548     result = true;
 549   } else if (new_start_aligned > cur_committed.start()) {
 550     // Shrink the committed region
 551 #if 0 // uncommitting space is currently unsafe because of the interactions
 552       // of growing and shrinking regions.  One region A can uncommit space
 553       // that it owns but which is being used by another region B (maybe).
 554       // Region B has not committed the space because it was already
 555       // committed by region A.
 556     MemRegion uncommit_region = committed_unique_to_self(changed_region,
 557       MemRegion(cur_committed.start(), new_start_aligned));
 558     if (!uncommit_region.is_empty()) {
 559       if (!os::uncommit_memory((char*)uncommit_region.start(),
 560                                uncommit_region.byte_size())) {
 561         // If the uncommit fails, ignore it.  Let the
 562         // committed table resizing go even though the committed
 563         // table will over state the committed space.
 564       }
 565     }
 566 #else
 567     assert(!result, "Should be false with current workaround");
 568 #endif
 569   }
 570   assert(_committed[changed_region].end() == cur_committed.end(),
 571     "end should not change");
 572   return result;
 573 }
 574 
 575 void PSCardTable::resize_update_committed_table(int changed_region,
 576                                                 MemRegion new_region) {
 577 
 578   CardValue* new_start = byte_for(new_region.start());
 579   // Set the new start of the committed region
 580   HeapWord* new_start_aligned = align_down((HeapWord*)new_start, os::vm_page_size());
 581   MemRegion new_committed = MemRegion(new_start_aligned,
 582                                       _committed[changed_region].end());
 583   _committed[changed_region] = new_committed;
 584   _committed[changed_region].set_start(new_start_aligned);
 585 }
 586 
 587 void PSCardTable::resize_update_card_table_entries(int changed_region,
 588                                                    MemRegion new_region) {
 589   debug_only(verify_guard();)
 590   MemRegion original_covered = _covered[changed_region];
 591   // Initialize the card entries.  Only consider the
 592   // region covered by the card table (_whole_heap)
 593   CardValue* entry;
 594   if (new_region.start() < _whole_heap.start()) {
 595     entry = byte_for(_whole_heap.start());
 596   } else {
 597     entry = byte_for(new_region.start());
 598   }
 599   CardValue* end = byte_for(original_covered.start());
 600   // If _whole_heap starts at the original covered regions start,
 601   // this loop will not execute.
 602   while (entry < end) { *entry++ = clean_card; }
 603 }
 604 
 605 void PSCardTable::resize_update_covered_table(int changed_region,
 606                                               MemRegion new_region) {
 607   // Update the covered region
 608   _covered[changed_region].set_start(new_region.start());
 609   _covered[changed_region].set_word_size(new_region.word_size());
 610 
 611   // reorder regions.  There should only be at most 1 out
 612   // of order.
 613   for (int i = _cur_covered_regions-1 ; i > 0; i--) {
 614     if (_covered[i].start() < _covered[i-1].start()) {
 615         MemRegion covered_mr = _covered[i-1];
 616         _covered[i-1] = _covered[i];
 617         _covered[i] = covered_mr;
 618         MemRegion committed_mr = _committed[i-1];
 619       _committed[i-1] = _committed[i];
 620       _committed[i] = committed_mr;
 621       break;
 622     }
 623   }
 624 #ifdef ASSERT
 625   for (int m = 0; m < _cur_covered_regions-1; m++) {
 626     assert(_covered[m].start() <= _covered[m+1].start(),
 627       "Covered regions out of order");
 628     assert(_committed[m].start() <= _committed[m+1].start(),
 629       "Committed regions out of order");
 630   }
 631 #endif
 632 }
 633 
 634 // Returns the start of any committed region that is lower than
 635 // the target committed region (index ind) and that intersects the
 636 // target region.  If none, return start of target region.
 637 //
 638 //      -------------
 639 //      |           |
 640 //      -------------
 641 //              ------------
 642 //              | target   |
 643 //              ------------
 644 //                               -------------
 645 //                               |           |
 646 //                               -------------
 647 //      ^ returns this
 648 //
 649 //      -------------
 650 //      |           |
 651 //      -------------
 652 //                      ------------
 653 //                      | target   |
 654 //                      ------------
 655 //                               -------------
 656 //                               |           |
 657 //                               -------------
 658 //                      ^ returns this
 659 
 660 HeapWord* PSCardTable::lowest_prev_committed_start(int ind) const {
 661   assert(_cur_covered_regions >= 0, "Expecting at least on region");
 662   HeapWord* min_start = _committed[ind].start();
 663   for (int j = 0; j < ind; j++) {
 664     HeapWord* this_start = _committed[j].start();
 665     if ((this_start < min_start) &&
 666         !(_committed[j].intersection(_committed[ind])).is_empty()) {
 667        min_start = this_start;
 668     }
 669   }
 670   return min_start;
 671 }
 672 
 673 bool PSCardTable::is_in_young(oop obj) const {
 674   return ParallelScavengeHeap::heap()->is_in_young(obj);
 675 }