1 /*
   2  * Copyright (c) 2007, 2015, 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/shared/cardTableModRefBS.hpp"
  27 #include "gc/shared/cardTableRS.hpp"
  28 #include "gc/shared/collectedHeap.hpp"
  29 #include "gc/shared/genCollectedHeap.hpp"
  30 #include "gc/shared/space.inline.hpp"
  31 #include "memory/allocation.inline.hpp"
  32 #include "memory/virtualspace.hpp"
  33 #include "oops/oop.inline.hpp"
  34 #include "runtime/java.hpp"
  35 #include "runtime/mutexLocker.hpp"
  36 #include "runtime/orderAccess.inline.hpp"
  37 #include "runtime/vmThread.hpp"
  38 
  39 void CardTableModRefBS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
  40                                                              OopsInGenClosure* cl,
  41                                                              CardTableRS* ct,
  42                                                              int n_threads) {
  43   assert(n_threads > 0, "Error: expected n_threads > 0");
  44   assert((n_threads == 1 && ParallelGCThreads == 0) ||
  45          n_threads <= (int)ParallelGCThreads,
  46          "# worker threads != # requested!");
  47   assert(!Thread::current()->is_VM_thread() || (n_threads == 1), "There is only 1 VM thread");
  48   assert(UseDynamicNumberOfGCThreads ||
  49          !FLAG_IS_DEFAULT(ParallelGCThreads) ||
  50          n_threads == (int)ParallelGCThreads,
  51          "# worker threads != # requested!");
  52   // Make sure the LNC array is valid for the space.
  53   jbyte**   lowest_non_clean;
  54   uintptr_t lowest_non_clean_base_chunk_index;
  55   size_t    lowest_non_clean_chunk_size;
  56   get_LNC_array_for_space(sp, lowest_non_clean,
  57                           lowest_non_clean_base_chunk_index,
  58                           lowest_non_clean_chunk_size);
  59 
  60   uint n_strides = n_threads * ParGCStridesPerThread;
  61   SequentialSubTasksDone* pst = sp->par_seq_tasks();
  62   // Sets the condition for completion of the subtask (how many threads
  63   // need to finish in order to be done).
  64   pst->set_n_threads(n_threads);
  65   pst->set_n_tasks(n_strides);
  66 
  67   uint stride = 0;
  68   while (!pst->is_task_claimed(/* reference */ stride)) {
  69     process_stride(sp, mr, stride, n_strides, cl, ct,
  70                    lowest_non_clean,
  71                    lowest_non_clean_base_chunk_index,
  72                    lowest_non_clean_chunk_size);
  73   }
  74   if (pst->all_tasks_completed()) {
  75     // Clear lowest_non_clean array for next time.
  76     intptr_t first_chunk_index = addr_to_chunk_index(mr.start());
  77     uintptr_t last_chunk_index  = addr_to_chunk_index(mr.last());
  78     for (uintptr_t ch = first_chunk_index; ch <= last_chunk_index; ch++) {
  79       intptr_t ind = ch - lowest_non_clean_base_chunk_index;
  80       assert(0 <= ind && ind < (intptr_t)lowest_non_clean_chunk_size,
  81              "Bounds error");
  82       lowest_non_clean[ind] = NULL;
  83     }
  84   }
  85 }
  86 
  87 void
  88 CardTableModRefBS::
  89 process_stride(Space* sp,
  90                MemRegion used,
  91                jint stride, int n_strides,
  92                OopsInGenClosure* cl,
  93                CardTableRS* ct,
  94                jbyte** lowest_non_clean,
  95                uintptr_t lowest_non_clean_base_chunk_index,
  96                size_t    lowest_non_clean_chunk_size) {
  97   // We go from higher to lower addresses here; it wouldn't help that much
  98   // because of the strided parallelism pattern used here.
  99 
 100   // Find the first card address of the first chunk in the stride that is
 101   // at least "bottom" of the used region.
 102   jbyte*    start_card  = byte_for(used.start());
 103   jbyte*    end_card    = byte_after(used.last());
 104   uintptr_t start_chunk = addr_to_chunk_index(used.start());
 105   uintptr_t start_chunk_stride_num = start_chunk % n_strides;
 106   jbyte* chunk_card_start;
 107 
 108   if ((uintptr_t)stride >= start_chunk_stride_num) {
 109     chunk_card_start = (jbyte*)(start_card +
 110                                 (stride - start_chunk_stride_num) *
 111                                 ParGCCardsPerStrideChunk);
 112   } else {
 113     // Go ahead to the next chunk group boundary, then to the requested stride.
 114     chunk_card_start = (jbyte*)(start_card +
 115                                 (n_strides - start_chunk_stride_num + stride) *
 116                                 ParGCCardsPerStrideChunk);
 117   }
 118 
 119   while (chunk_card_start < end_card) {
 120     // Even though we go from lower to higher addresses below, the
 121     // strided parallelism can interleave the actual processing of the
 122     // dirty pages in various ways. For a specific chunk within this
 123     // stride, we take care to avoid double scanning or missing a card
 124     // by suitably initializing the "min_done" field in process_chunk_boundaries()
 125     // below, together with the dirty region extension accomplished in
 126     // DirtyCardToOopClosure::do_MemRegion().
 127     jbyte*    chunk_card_end = chunk_card_start + ParGCCardsPerStrideChunk;
 128     // Invariant: chunk_mr should be fully contained within the "used" region.
 129     MemRegion chunk_mr       = MemRegion(addr_for(chunk_card_start),
 130                                          chunk_card_end >= end_card ?
 131                                            used.end() : addr_for(chunk_card_end));
 132     assert(chunk_mr.word_size() > 0, "[chunk_card_start > used_end)");
 133     assert(used.contains(chunk_mr), "chunk_mr should be subset of used");
 134 
 135     DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(),
 136                                                      cl->gen_boundary());
 137     ClearNoncleanCardWrapper clear_cl(dcto_cl, ct);
 138 
 139 
 140     // Process the chunk.
 141     process_chunk_boundaries(sp,
 142                              dcto_cl,
 143                              chunk_mr,
 144                              used,
 145                              lowest_non_clean,
 146                              lowest_non_clean_base_chunk_index,
 147                              lowest_non_clean_chunk_size);
 148 
 149     // We want the LNC array updates above in process_chunk_boundaries
 150     // to be visible before any of the card table value changes as a
 151     // result of the dirty card iteration below.
 152     OrderAccess::storestore();
 153 
 154     // We want to clear the cards: clear_cl here does the work of finding
 155     // contiguous dirty ranges of cards to process and clear.
 156     clear_cl.do_MemRegion(chunk_mr);
 157 
 158     // Find the next chunk of the stride.
 159     chunk_card_start += ParGCCardsPerStrideChunk * n_strides;
 160   }
 161 }
 162 
 163 
 164 // If you want a talkative process_chunk_boundaries,
 165 // then #define NOISY(x) x
 166 #ifdef NOISY
 167 #error "Encountered a global preprocessor flag, NOISY, which might clash with local definition to follow"
 168 #else
 169 #define NOISY(x)
 170 #endif
 171 
 172 void
 173 CardTableModRefBS::
 174 process_chunk_boundaries(Space* sp,
 175                          DirtyCardToOopClosure* dcto_cl,
 176                          MemRegion chunk_mr,
 177                          MemRegion used,
 178                          jbyte** lowest_non_clean,
 179                          uintptr_t lowest_non_clean_base_chunk_index,
 180                          size_t    lowest_non_clean_chunk_size)
 181 {
 182   // We must worry about non-array objects that cross chunk boundaries,
 183   // because such objects are both precisely and imprecisely marked:
 184   // .. if the head of such an object is dirty, the entire object
 185   //    needs to be scanned, under the interpretation that this
 186   //    was an imprecise mark
 187   // .. if the head of such an object is not dirty, we can assume
 188   //    precise marking and it's efficient to scan just the dirty
 189   //    cards.
 190   // In either case, each scanned reference must be scanned precisely
 191   // once so as to avoid cloning of a young referent. For efficiency,
 192   // our closures depend on this property and do not protect against
 193   // double scans.
 194 
 195   uintptr_t start_chunk_index = addr_to_chunk_index(chunk_mr.start());
 196   assert(start_chunk_index >= lowest_non_clean_base_chunk_index, "Bounds error.");
 197   uintptr_t cur_chunk_index   = start_chunk_index - lowest_non_clean_base_chunk_index;
 198 
 199   NOISY(tty->print_cr("===========================================================================");)
 200   NOISY(tty->print_cr(" process_chunk_boundary: Called with [" PTR_FORMAT "," PTR_FORMAT ")",
 201                       chunk_mr.start(), chunk_mr.end());)
 202 
 203   // First, set "our" lowest_non_clean entry, which would be
 204   // used by the thread scanning an adjoining left chunk with
 205   // a non-array object straddling the mutual boundary.
 206   // Find the object that spans our boundary, if one exists.
 207   // first_block is the block possibly straddling our left boundary.
 208   HeapWord* first_block = sp->block_start(chunk_mr.start());
 209   assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()),
 210          "First chunk should always have a co-initial block");
 211   // Does the block straddle the chunk's left boundary, and is it
 212   // a non-array object?
 213   if (first_block < chunk_mr.start()        // first block straddles left bdry
 214       && sp->block_is_obj(first_block)      // first block is an object
 215       && !(oop(first_block)->is_objArray()  // first block is not an array (arrays are precisely dirtied)
 216            || oop(first_block)->is_typeArray())) {
 217     // Find our least non-clean card, so that a left neighbor
 218     // does not scan an object straddling the mutual boundary
 219     // too far to the right, and attempt to scan a portion of
 220     // that object twice.
 221     jbyte* first_dirty_card = NULL;
 222     jbyte* last_card_of_first_obj =
 223         byte_for(first_block + sp->block_size(first_block) - 1);
 224     jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
 225     jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last());
 226     jbyte* last_card_to_check =
 227       (jbyte*) MIN2((intptr_t) last_card_of_cur_chunk,
 228                     (intptr_t) last_card_of_first_obj);
 229     // Note that this does not need to go beyond our last card
 230     // if our first object completely straddles this chunk.
 231     for (jbyte* cur = first_card_of_cur_chunk;
 232          cur <= last_card_to_check; cur++) {
 233       jbyte val = *cur;
 234       if (card_will_be_scanned(val)) {
 235         first_dirty_card = cur; break;
 236       } else {
 237         assert(!card_may_have_been_dirty(val), "Error");
 238       }
 239     }
 240     if (first_dirty_card != NULL) {
 241       NOISY(tty->print_cr(" LNC: Found a dirty card at " PTR_FORMAT " in current chunk",
 242                     first_dirty_card);)
 243       assert(cur_chunk_index < lowest_non_clean_chunk_size, "Bounds error.");
 244       assert(lowest_non_clean[cur_chunk_index] == NULL,
 245              "Write exactly once : value should be stable hereafter for this round");
 246       lowest_non_clean[cur_chunk_index] = first_dirty_card;
 247     } NOISY(else {
 248       tty->print_cr(" LNC: Found no dirty card in current chunk; leaving LNC entry NULL");
 249       // In the future, we could have this thread look for a non-NULL value to copy from its
 250       // right neighbor (up to the end of the first object).
 251       if (last_card_of_cur_chunk < last_card_of_first_obj) {
 252         tty->print_cr(" LNC: BEWARE!!! first obj straddles past right end of chunk:\n"
 253                       "   might be efficient to get value from right neighbor?");
 254       }
 255     })
 256   } else {
 257     // In this case we can help our neighbor by just asking them
 258     // to stop at our first card (even though it may not be dirty).
 259     NOISY(tty->print_cr(" LNC: first block is not a non-array object; setting LNC to first card of current chunk");)
 260     assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter");
 261     jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
 262     lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk;
 263   }
 264   NOISY(tty->print_cr(" process_chunk_boundary: lowest_non_clean[" INTPTR_FORMAT "] = " PTR_FORMAT
 265                 "   which corresponds to the heap address " PTR_FORMAT,
 266                 cur_chunk_index, lowest_non_clean[cur_chunk_index],
 267                 (lowest_non_clean[cur_chunk_index] != NULL)
 268                 ? addr_for(lowest_non_clean[cur_chunk_index])
 269                 : NULL);)
 270   NOISY(tty->print_cr("---------------------------------------------------------------------------");)
 271 
 272   // Next, set our own max_to_do, which will strictly/exclusively bound
 273   // the highest address that we will scan past the right end of our chunk.
 274   HeapWord* max_to_do = NULL;
 275   if (chunk_mr.end() < used.end()) {
 276     // This is not the last chunk in the used region.
 277     // What is our last block? We check the first block of
 278     // the next (right) chunk rather than strictly check our last block
 279     // because it's potentially more efficient to do so.
 280     HeapWord* const last_block = sp->block_start(chunk_mr.end());
 281     assert(last_block <= chunk_mr.end(), "In case this property changes.");
 282     if ((last_block == chunk_mr.end())     // our last block does not straddle boundary
 283         || !sp->block_is_obj(last_block)   // last_block isn't an object
 284         || oop(last_block)->is_objArray()  // last_block is an array (precisely marked)
 285         || oop(last_block)->is_typeArray()) {
 286       max_to_do = chunk_mr.end();
 287       NOISY(tty->print_cr(" process_chunk_boundary: Last block on this card is not a non-array object;\n"
 288                          "   max_to_do left at " PTR_FORMAT, max_to_do);)
 289     } else {
 290       assert(last_block < chunk_mr.end(), "Tautology");
 291       // It is a non-array object that straddles the right boundary of this chunk.
 292       // last_obj_card is the card corresponding to the start of the last object
 293       // in the chunk.  Note that the last object may not start in
 294       // the chunk.
 295       jbyte* const last_obj_card = byte_for(last_block);
 296       const jbyte val = *last_obj_card;
 297       if (!card_will_be_scanned(val)) {
 298         assert(!card_may_have_been_dirty(val), "Error");
 299         // The card containing the head is not dirty.  Any marks on
 300         // subsequent cards still in this chunk must have been made
 301         // precisely; we can cap processing at the end of our chunk.
 302         max_to_do = chunk_mr.end();
 303         NOISY(tty->print_cr(" process_chunk_boundary: Head of last object on this card is not dirty;\n"
 304                             "   max_to_do left at " PTR_FORMAT,
 305                             max_to_do);)
 306       } else {
 307         // The last object must be considered dirty, and extends onto the
 308         // following chunk.  Look for a dirty card in that chunk that will
 309         // bound our processing.
 310         jbyte* limit_card = NULL;
 311         const size_t last_block_size = sp->block_size(last_block);
 312         jbyte* const last_card_of_last_obj =
 313           byte_for(last_block + last_block_size - 1);
 314         jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end());
 315         // This search potentially goes a long distance looking
 316         // for the next card that will be scanned, terminating
 317         // at the end of the last_block, if no earlier dirty card
 318         // is found.
 319         assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk,
 320                "last card of next chunk may be wrong");
 321         for (jbyte* cur = first_card_of_next_chunk;
 322              cur <= last_card_of_last_obj; cur++) {
 323           const jbyte val = *cur;
 324           if (card_will_be_scanned(val)) {
 325             NOISY(tty->print_cr(" Found a non-clean card " PTR_FORMAT " with value 0x%x",
 326                                 cur, (int)val);)
 327             limit_card = cur; break;
 328           } else {
 329             assert(!card_may_have_been_dirty(val), "Error: card can't be skipped");
 330           }
 331         }
 332         if (limit_card != NULL) {
 333           max_to_do = addr_for(limit_card);
 334           assert(limit_card != NULL && max_to_do != NULL, "Error");
 335           NOISY(tty->print_cr(" process_chunk_boundary: Found a dirty card at " PTR_FORMAT
 336                         "   max_to_do set at " PTR_FORMAT " which is before end of last block in chunk: "
 337                         PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,
 338                         limit_card, max_to_do, last_block, last_block_size, (last_block+last_block_size));)
 339         } else {
 340           // The following is a pessimistic value, because it's possible
 341           // that a dirty card on a subsequent chunk has been cleared by
 342           // the time we get to look at it; we'll correct for that further below,
 343           // using the LNC array which records the least non-clean card
 344           // before cards were cleared in a particular chunk.
 345           limit_card = last_card_of_last_obj;
 346           max_to_do = last_block + last_block_size;
 347           assert(limit_card != NULL && max_to_do != NULL, "Error");
 348           NOISY(tty->print_cr(" process_chunk_boundary: Found no dirty card before end of last block in chunk\n"
 349                               "   Setting limit_card to " PTR_FORMAT
 350                               " and max_to_do " PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,
 351                               limit_card, last_block, last_block_size, max_to_do);)
 352         }
 353         assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size,
 354                "Bounds error.");
 355         // It is possible that a dirty card for the last object may have been
 356         // cleared before we had a chance to examine it. In that case, the value
 357         // will have been logged in the LNC for that chunk.
 358         // We need to examine as many chunks to the right as this object
 359         // covers. However, we need to bound this checking to the largest
 360         // entry in the LNC array: this is because the heap may expand
 361         // after the LNC array has been created but before we reach this point,
 362         // and the last block in our chunk may have been expanded to include
 363         // the expansion delta (and possibly subsequently allocated from, so
 364         // it wouldn't be sufficient to check whether that last block was
 365         // or was not an object at this point).
 366         uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1)
 367                                               - lowest_non_clean_base_chunk_index;
 368         const uintptr_t last_chunk_index    = addr_to_chunk_index(used.last())
 369                                               - lowest_non_clean_base_chunk_index;
 370         if (last_chunk_index_to_check > last_chunk_index) {
 371           assert(last_block + last_block_size > used.end(),
 372                  err_msg("Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]"
 373                          " does not exceed used.end() = " PTR_FORMAT ","
 374                          " yet last_chunk_index_to_check " INTPTR_FORMAT
 375                          " exceeds last_chunk_index " INTPTR_FORMAT,
 376                          p2i(last_block), p2i(last_block + last_block_size),
 377                          p2i(used.end()),
 378                          last_chunk_index_to_check, last_chunk_index));
 379           assert(sp->used_region().end() > used.end(),
 380                  err_msg("Expansion did not happen: "
 381                          "[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")",
 382                          p2i(sp->used_region().start()), p2i(sp->used_region().end()),
 383                          p2i(used.start()), p2i(used.end())));
 384           NOISY(tty->print_cr(" process_chunk_boundary: heap expanded; explicitly bounding last_chunk");)
 385           last_chunk_index_to_check = last_chunk_index;
 386         }
 387         for (uintptr_t lnc_index = cur_chunk_index + 1;
 388              lnc_index <= last_chunk_index_to_check;
 389              lnc_index++) {
 390           jbyte* lnc_card = lowest_non_clean[lnc_index];
 391           if (lnc_card != NULL) {
 392             // we can stop at the first non-NULL entry we find
 393             if (lnc_card <= limit_card) {
 394               NOISY(tty->print_cr(" process_chunk_boundary: LNC card " PTR_FORMAT " is lower than limit_card " PTR_FORMAT,
 395                                   "   max_to_do will be lowered to " PTR_FORMAT " from " PTR_FORMAT,
 396                                   lnc_card, limit_card, addr_for(lnc_card), max_to_do);)
 397               limit_card = lnc_card;
 398               max_to_do = addr_for(limit_card);
 399               assert(limit_card != NULL && max_to_do != NULL, "Error");
 400             }
 401             // In any case, we break now
 402             break;
 403           }  // else continue to look for a non-NULL entry if any
 404         }
 405         assert(limit_card != NULL && max_to_do != NULL, "Error");
 406       }
 407       assert(max_to_do != NULL, "OOPS 1 !");
 408     }
 409     assert(max_to_do != NULL, "OOPS 2!");
 410   } else {
 411     max_to_do = used.end();
 412     NOISY(tty->print_cr(" process_chunk_boundary: Last chunk of this space;\n"
 413                   "   max_to_do left at " PTR_FORMAT,
 414                   max_to_do);)
 415   }
 416   assert(max_to_do != NULL, "OOPS 3!");
 417   // Now we can set the closure we're using so it doesn't to beyond
 418   // max_to_do.
 419   dcto_cl->set_min_done(max_to_do);
 420 #ifndef PRODUCT
 421   dcto_cl->set_last_bottom(max_to_do);
 422 #endif
 423   NOISY(tty->print_cr("===========================================================================\n");)
 424 }
 425 
 426 #undef NOISY
 427 
 428 void
 429 CardTableModRefBS::
 430 get_LNC_array_for_space(Space* sp,
 431                         jbyte**& lowest_non_clean,
 432                         uintptr_t& lowest_non_clean_base_chunk_index,
 433                         size_t& lowest_non_clean_chunk_size) {
 434 
 435   int       i        = find_covering_region_containing(sp->bottom());
 436   MemRegion covered  = _covered[i];
 437   size_t    n_chunks = chunks_to_cover(covered);
 438 
 439   // Only the first thread to obtain the lock will resize the
 440   // LNC array for the covered region.  Any later expansion can't affect
 441   // the used_at_save_marks region.
 442   // (I observed a bug in which the first thread to execute this would
 443   // resize, and then it would cause "expand_and_allocate" that would
 444   // increase the number of chunks in the covered region.  Then a second
 445   // thread would come and execute this, see that the size didn't match,
 446   // and free and allocate again.  So the first thread would be using a
 447   // freed "_lowest_non_clean" array.)
 448 
 449   // Do a dirty read here. If we pass the conditional then take the rare
 450   // event lock and do the read again in case some other thread had already
 451   // succeeded and done the resize.
 452   int cur_collection = GenCollectedHeap::heap()->total_collections();
 453   if (_last_LNC_resizing_collection[i] != cur_collection) {
 454     MutexLocker x(ParGCRareEvent_lock);
 455     if (_last_LNC_resizing_collection[i] != cur_collection) {
 456       if (_lowest_non_clean[i] == NULL ||
 457           n_chunks != _lowest_non_clean_chunk_size[i]) {
 458 
 459         // Should we delete the old?
 460         if (_lowest_non_clean[i] != NULL) {
 461           assert(n_chunks != _lowest_non_clean_chunk_size[i],
 462                  "logical consequence");
 463           FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i]);
 464           _lowest_non_clean[i] = NULL;
 465         }
 466         // Now allocate a new one if necessary.
 467         if (_lowest_non_clean[i] == NULL) {
 468           _lowest_non_clean[i]                  = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC);
 469           _lowest_non_clean_chunk_size[i]       = n_chunks;
 470           _lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start());
 471           for (int j = 0; j < (int)n_chunks; j++)
 472             _lowest_non_clean[i][j] = NULL;
 473         }
 474       }
 475       _last_LNC_resizing_collection[i] = cur_collection;
 476     }
 477   }
 478   // In any case, now do the initialization.
 479   lowest_non_clean                  = _lowest_non_clean[i];
 480   lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i];
 481   lowest_non_clean_chunk_size       = _lowest_non_clean_chunk_size[i];
 482 }