1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   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.
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   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  *
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
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  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_GC_SHARED_SPACE_INLINE_HPP
  26 #define SHARE_VM_GC_SHARED_SPACE_INLINE_HPP
  27 
  28 #include "gc/serial/markSweep.inline.hpp"
  29 #include "gc/shared/collectedHeap.hpp"
  30 #include "gc/shared/generation.hpp"
  31 #include "gc/shared/space.hpp"
  32 #include "gc/shared/spaceDecorator.hpp"
  33 #include "memory/universe.hpp"
  34 #include "oops/oopsHierarchy.hpp"
  35 #include "runtime/prefetch.inline.hpp"
  36 #include "runtime/safepoint.hpp"
  37 
  38 inline HeapWord* Space::block_start(const void* p) {
  39   return block_start_const(p);
  40 }
  41 
  42 inline HeapWord* OffsetTableContigSpace::allocate(size_t size) {
  43   HeapWord* res = ContiguousSpace::allocate(size);
  44   if (res != NULL) {
  45     _offsets.alloc_block(res, size);
  46   }
  47   return res;
  48 }
  49 
  50 // Because of the requirement of keeping "_offsets" up to date with the
  51 // allocations, we sequentialize these with a lock.  Therefore, best if
  52 // this is used for larger LAB allocations only.
  53 inline HeapWord* OffsetTableContigSpace::par_allocate(size_t size) {
  54   MutexLocker x(&_par_alloc_lock);
  55   // This ought to be just "allocate", because of the lock above, but that
  56   // ContiguousSpace::allocate asserts that either the allocating thread
  57   // holds the heap lock or it is the VM thread and we're at a safepoint.
  58   // The best I (dld) could figure was to put a field in ContiguousSpace
  59   // meaning "locking at safepoint taken care of", and set/reset that
  60   // here.  But this will do for now, especially in light of the comment
  61   // above.  Perhaps in the future some lock-free manner of keeping the
  62   // coordination.
  63   HeapWord* res = ContiguousSpace::par_allocate(size);
  64   if (res != NULL) {
  65     _offsets.alloc_block(res, size);
  66   }
  67   return res;
  68 }
  69 
  70 inline HeapWord*
  71 OffsetTableContigSpace::block_start_const(const void* p) const {
  72   return _offsets.block_start(p);
  73 }
  74 
  75 size_t CompactibleSpace::obj_size(const HeapWord* addr) const {
  76   return oop(addr)->size();
  77 }
  78 
  79 class DeadSpacer : StackObj {
  80   size_t _allowed_deadspace_words;
  81   bool _active;
  82   CompactibleSpace* _space;
  83 
  84 public:
  85   DeadSpacer(CompactibleSpace* space) : _space(space), _allowed_deadspace_words(0) {
  86     size_t ratio = _space->allowed_dead_ratio();
  87     _active = ratio > 0;
  88 
  89     if (_active) {
  90       assert(!UseG1GC, "G1 should not be using dead space");
  91 
  92       // We allow some amount of garbage towards the bottom of the space, so
  93       // we don't start compacting before there is a significant gain to be made.
  94       // Occasionally, we want to ensure a full compaction, which is determined
  95       // by the MarkSweepAlwaysCompactCount parameter.
  96       if ((MarkSweep::total_invocations() % MarkSweepAlwaysCompactCount) != 0) {
  97         _allowed_deadspace_words = (space->capacity() * ratio / 100) / HeapWordSize;
  98       } else {
  99         _active = false;
 100       }
 101     }
 102   }
 103 
 104 
 105   bool insert_deadspace(HeapWord* dead_start, HeapWord* dead_end) {
 106     if (!_active) {
 107       return false;
 108     }
 109 
 110     size_t dead_length = pointer_delta(dead_end, dead_start);
 111     if (_allowed_deadspace_words >= dead_length) {
 112       _allowed_deadspace_words -= dead_length;
 113       CollectedHeap::fill_with_object(dead_start, dead_length);
 114       oop obj = oop(dead_start);
 115       obj->set_mark(obj->mark()->set_marked());
 116 
 117       assert(dead_length == (size_t)obj->size(), "bad filler object size");
 118       log_develop_trace(gc, compaction)("Inserting object to dead space: " PTR_FORMAT ", " PTR_FORMAT ", " SIZE_FORMAT "b",
 119           p2i(dead_start), p2i(dead_end), dead_length * HeapWordSize);
 120 
 121       return true;
 122     } else {
 123       _active = false;
 124       return false;
 125     }
 126   }
 127 
 128 };
 129 
 130 template <class SpaceType>
 131 inline void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp) {
 132   // Compute the new addresses for the live objects and store it in the mark
 133   // Used by universe::mark_sweep_phase2()
 134 
 135   // We're sure to be here before any objects are compacted into this
 136   // space, so this is a good time to initialize this:
 137   space->set_compaction_top(space->bottom());
 138 
 139   if (cp->space == NULL) {
 140     assert(cp->gen != NULL, "need a generation");
 141     assert(cp->threshold == NULL, "just checking");
 142     assert(cp->gen->first_compaction_space() == space, "just checking");
 143     cp->space = cp->gen->first_compaction_space();
 144     cp->threshold = cp->space->initialize_threshold();
 145     cp->space->set_compaction_top(cp->space->bottom());
 146   }
 147 
 148   HeapWord* compact_top = cp->space->compaction_top(); // This is where we are currently compacting to.
 149 
 150   DeadSpacer dead_spacer(space);
 151 
 152   HeapWord*  end_of_live = space->bottom();  // One byte beyond the last byte of the last live object.
 153   HeapWord*  first_dead = NULL; // The first dead object.
 154 
 155   const intx interval = PrefetchScanIntervalInBytes;
 156 
 157   HeapWord* cur_obj = space->bottom();
 158   HeapWord* scan_limit = space->scan_limit();
 159 
 160   while (cur_obj < scan_limit) {
 161     assert(!space->scanned_block_is_obj(cur_obj) ||
 162            oop(cur_obj)->mark()->is_marked() || oop(cur_obj)->mark()->is_unlocked() ||
 163            oop(cur_obj)->mark()->has_bias_pattern(),
 164            "these are the only valid states during a mark sweep");
 165     if (space->scanned_block_is_obj(cur_obj) && oop(cur_obj)->is_gc_marked()) {
 166       // prefetch beyond cur_obj
 167       Prefetch::write(cur_obj, interval);
 168       size_t size = space->scanned_block_size(cur_obj);
 169       compact_top = cp->space->forward(oop(cur_obj), size, cp, compact_top);
 170       cur_obj += size;
 171       end_of_live = cur_obj;
 172     } else {
 173       // run over all the contiguous dead objects
 174       HeapWord* end = cur_obj;
 175       do {
 176         // prefetch beyond end
 177         Prefetch::write(end, interval);
 178         end += space->scanned_block_size(end);
 179       } while (end < scan_limit && (!space->scanned_block_is_obj(end) || !oop(end)->is_gc_marked()));
 180 
 181       // see if we might want to pretend this object is alive so that
 182       // we don't have to compact quite as often.
 183       if (cur_obj == compact_top && dead_spacer.insert_deadspace(cur_obj, end)) {
 184         oop obj = oop(cur_obj);
 185         compact_top = cp->space->forward(obj, obj->size(), cp, compact_top);
 186         end_of_live = end;
 187       } else {
 188         // otherwise, it really is a free region.
 189 
 190         // cur_obj is a pointer to a dead object. Use this dead memory to store a pointer to the next live object.
 191         *(HeapWord**)cur_obj = end;
 192 
 193         // see if this is the first dead region.
 194         if (first_dead == NULL) {
 195           first_dead = cur_obj;
 196         }
 197       }
 198 
 199       // move on to the next object
 200       cur_obj = end;
 201     }
 202   }
 203 
 204   assert(cur_obj == scan_limit, "just checking");
 205   space->_end_of_live = end_of_live;
 206   if (first_dead != NULL) {
 207     space->_first_dead = first_dead;
 208   } else {
 209     space->_first_dead = end_of_live;
 210   }
 211 
 212   // save the compaction_top of the compaction space.
 213   cp->space->set_compaction_top(compact_top);
 214 }
 215 
 216 template <class SpaceType>
 217 inline void CompactibleSpace::scan_and_adjust_pointers(SpaceType* space) {
 218   // adjust all the interior pointers to point at the new locations of objects
 219   // Used by MarkSweep::mark_sweep_phase3()
 220 
 221   HeapWord* cur_obj = space->bottom();
 222   HeapWord* const end_of_live = space->_end_of_live;  // Established by "scan_and_forward".
 223   HeapWord* const first_dead = space->_first_dead;    // Established by "scan_and_forward".
 224 
 225   assert(first_dead <= end_of_live, "Stands to reason, no?");
 226 
 227   const intx interval = PrefetchScanIntervalInBytes;
 228 
 229   debug_only(HeapWord* prev_obj = NULL);
 230   while (cur_obj < end_of_live) {
 231     Prefetch::write(cur_obj, interval);
 232     if (cur_obj < first_dead || oop(cur_obj)->is_gc_marked()) {
 233       // cur_obj is alive
 234       // point all the oops to the new location
 235       size_t size = MarkSweep::adjust_pointers(oop(cur_obj));
 236       size = space->adjust_obj_size(size);
 237       debug_only(prev_obj = cur_obj);
 238       cur_obj += size;
 239     } else {
 240       debug_only(prev_obj = cur_obj);
 241       // cur_obj is not a live object, instead it points at the next live object
 242       cur_obj = *(HeapWord**)cur_obj;
 243       assert(cur_obj > prev_obj, "we should be moving forward through memory, cur_obj: " PTR_FORMAT ", prev_obj: " PTR_FORMAT, p2i(cur_obj), p2i(prev_obj));
 244     }
 245   }
 246 
 247   assert(cur_obj == end_of_live, "just checking");
 248 }
 249 
 250 #ifdef ASSERT
 251 template <class SpaceType>
 252 inline void CompactibleSpace::verify_up_to_first_dead(SpaceType* space) {
 253   HeapWord* cur_obj = space->bottom();
 254 
 255   if (cur_obj < space->_end_of_live && space->_first_dead > cur_obj && !oop(cur_obj)->is_gc_marked()) {
 256      // we have a chunk of the space which hasn't moved and we've reinitialized
 257      // the mark word during the previous pass, so we can't use is_gc_marked for
 258      // the traversal.
 259      HeapWord* prev_obj = NULL;
 260 
 261      while (cur_obj < space->_first_dead) {
 262        size_t size = space->obj_size(cur_obj);
 263        assert(!oop(cur_obj)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
 264        prev_obj = cur_obj;
 265        cur_obj += size;
 266      }
 267   }
 268 }
 269 #endif
 270 
 271 template <class SpaceType>
 272 inline void CompactibleSpace::clear_empty_region(SpaceType* space) {
 273   // Let's remember if we were empty before we did the compaction.
 274   bool was_empty = space->used_region().is_empty();
 275   // Reset space after compaction is complete
 276   space->reset_after_compaction();
 277   // We do this clear, below, since it has overloaded meanings for some
 278   // space subtypes.  For example, OffsetTableContigSpace's that were
 279   // compacted into will have had their offset table thresholds updated
 280   // continuously, but those that weren't need to have their thresholds
 281   // re-initialized.  Also mangles unused area for debugging.
 282   if (space->used_region().is_empty()) {
 283     if (!was_empty) space->clear(SpaceDecorator::Mangle);
 284   } else {
 285     if (ZapUnusedHeapArea) space->mangle_unused_area();
 286   }
 287 }
 288 
 289 template <class SpaceType>
 290 inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
 291   // Copy all live objects to their new location
 292   // Used by MarkSweep::mark_sweep_phase4()
 293 
 294   verify_up_to_first_dead(space);
 295 
 296   HeapWord* const bottom = space->bottom();
 297   HeapWord* const end_of_live = space->_end_of_live;
 298 
 299   assert(space->_first_dead <= end_of_live, "Invariant. _first_dead: " PTR_FORMAT " <= end_of_live: " PTR_FORMAT, p2i(space->_first_dead), p2i(end_of_live));
 300   if (space->_first_dead == end_of_live && (bottom == end_of_live || !oop(bottom)->is_gc_marked())) {
 301     // Nothing to compact. The space is either empty or all live object should be left in place.
 302     clear_empty_region(space);
 303     return;
 304   }
 305 
 306   const intx scan_interval = PrefetchScanIntervalInBytes;
 307   const intx copy_interval = PrefetchCopyIntervalInBytes;
 308 
 309   assert(bottom < end_of_live, "bottom: " PTR_FORMAT " should be < end_of_live: " PTR_FORMAT, p2i(bottom), p2i(end_of_live));
 310   HeapWord* cur_obj = bottom;
 311   if (space->_first_dead > cur_obj && !oop(cur_obj)->is_gc_marked()) {
 312     // All object before _first_dead can be skipped. They should not be moved.
 313     // A pointer to the first live object is stored at the memory location for _first_dead.
 314     cur_obj = *(HeapWord**)(space->_first_dead);
 315   }
 316 
 317   debug_only(HeapWord* prev_obj = NULL);
 318   while (cur_obj < end_of_live) {
 319     if (!oop(cur_obj)->is_gc_marked()) {
 320       debug_only(prev_obj = cur_obj);
 321       // The first word of the dead object contains a pointer to the next live object or end of space.
 322       cur_obj = *(HeapWord**)cur_obj;
 323       assert(cur_obj > prev_obj, "we should be moving forward through memory");
 324     } else {
 325       // prefetch beyond q
 326       Prefetch::read(cur_obj, scan_interval);
 327 
 328       // size and destination
 329       size_t size = space->obj_size(cur_obj);
 330       HeapWord* compaction_top = (HeapWord*)oop(cur_obj)->forwardee();
 331 
 332       // prefetch beyond compaction_top
 333       Prefetch::write(compaction_top, copy_interval);
 334 
 335       // copy object and reinit its mark
 336       assert(cur_obj != compaction_top, "everything in this pass should be moving");
 337       Copy::aligned_conjoint_words(cur_obj, compaction_top, size);
 338       oop(compaction_top)->init_mark();
 339       assert(oop(compaction_top)->klass() != NULL, "should have a class");
 340 
 341       debug_only(prev_obj = cur_obj);
 342       cur_obj += size;
 343     }
 344   }
 345 
 346   clear_empty_region(space);
 347 }
 348 
 349 size_t ContiguousSpace::scanned_block_size(const HeapWord* addr) const {
 350   return oop(addr)->size();
 351 }
 352 
 353 #endif // SHARE_VM_GC_SHARED_SPACE_INLINE_HPP