truffle: src/share/vm/gc_implementation/parNew/parNewGeneration.cpp comparison

comparison src/share/vm/gc_implementation/parNew/parNewGeneration.cpp @ 679:cea947c8a988

6819891: ParNew: Fix work queue overflow code to deal correctly with +UseCompressedOops Summary: When using compressed oops, rather than chaining the overflowed grey objects' pre-images through their klass words, we use GC-worker thread-local overflow stacks. Reviewed-by: jcoomes, jmasa

author	ysr
date	Sat, 28 Mar 2009 15:47:29 -0700
parents	0fbdb4381b99
children	becb17ad5e51

comparison

equal deleted inserted replaced

-:4ac7d97e6101
+:cea947c8a988
 Generation* old_gen_,
 int thread_num_,
 ObjToScanQueueSet* work_queue_set_,
 size_t desired_plab_sz_,
 ParallelTaskTerminator& term_) :
-_to_space(to_space_), _old_gen(old_gen_), _thread_num(thread_num_),
+_to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_),
 _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),
 _ageTable(false), // false ==> not the global age table, no perf data.
 _to_space_alloc_buffer(desired_plab_sz_),
 _to_space_closure(gen_, this), _old_gen_closure(gen_, this),
 _to_space_root_closure(gen_, this), _old_gen_root_closure(gen_, this),
 (ChunkArray*) old_gen()->get_data_recorder(thread_num());
 _hash_seed = 17;  // Might want to take time-based random value.
 _start = os::elapsedTime();
 _old_gen_closure.set_generation(old_gen_);
 _old_gen_root_closure.set_generation(old_gen_);
+if (UseCompressedOops) {
+_overflow_stack = new (ResourceObj::C_HEAP) GrowableArray<oop>(512, true);
+} else {
+_overflow_stack = NULL;
+}
 }
 #ifdef _MSC_VER
 #pragma warning( pop )
 #endif
 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
 assert(old->is_objArray(), "must be obj array");
 assert(old->is_forwarded(), "must be forwarded");
 assert(Universe::heap()->is_in_reserved(old), "must be in heap.");
-assert(!_old_gen->is_in(old), "must be in young generation.");
+assert(!old_gen()->is_in(old), "must be in young generation.");
 objArrayOop obj = objArrayOop(old->forwardee());
 // Process ParGCArrayScanChunk elements now
 // and push the remainder back onto queue
 int start     = arrayOop(old)->length();
 }
 void ParScanThreadState::trim_queues(int max_size) {
 ObjToScanQueue* queue = work_queue();
-while (queue->size() > (juint)max_size) {
+do {
-oop obj_to_scan;
+while (queue->size() > (juint)max_size) {
-if (queue->pop_local(obj_to_scan)) {
+oop obj_to_scan;
-note_pop();
+if (queue->pop_local(obj_to_scan)) {
+note_pop();
 if ((HeapWord *)obj_to_scan < young_old_boundary()) {
 if (obj_to_scan->is_objArray() &&
 obj_to_scan->is_forwarded() &&
 obj_to_scan->forwardee() != obj_to_scan) {
 scan_partial_array_and_push_remainder(obj_to_scan);
+} else {
+// object is in to_space
+obj_to_scan->oop_iterate(&_to_space_closure);
+}
 } else {
-// object is in to_space
+// object is in old generation
-obj_to_scan->oop_iterate(&_to_space_closure);
+obj_to_scan->oop_iterate(&_old_gen_closure);
 }
-} else {
-// object is in old generation
-obj_to_scan->oop_iterate(&_old_gen_closure);
 }
 }
-}
+// For the  case of compressed oops, we have a private, non-shared
+// overflow stack, so we eagerly drain it so as to more evenly
+// distribute load early. Note: this may be good to do in
+// general rather than delay for the final stealing phase.
+// If applicable, we'll transfer a set of objects over to our
+// work queue, allowing them to be stolen and draining our
+// private overflow stack.
+} while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
+}
+bool ParScanThreadState::take_from_overflow_stack() {
+assert(UseCompressedOops, "Else should not call");
+assert(young_gen()->overflow_list() == NULL, "Error");
+ObjToScanQueue* queue = work_queue();
+GrowableArray<oop>* of_stack = overflow_stack();
+uint num_overflow_elems = of_stack->length();
+uint num_take_elems     = MIN2(MIN2((queue->max_elems() - queue->size())/4,
+(juint)ParGCDesiredObjsFromOverflowList),
+num_overflow_elems);
+// Transfer the most recent num_take_elems from the overflow
+// stack to our work queue.
+for (size_t i = 0; i != num_take_elems; i++) {
+oop cur = of_stack->pop();
+oop obj_to_push = cur->forwardee();
+assert(Universe::heap()->is_in_reserved(cur), "Should be in heap");
+assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
+assert(Universe::heap()->is_in_reserved(obj_to_push), "Should be in heap");
+if (should_be_partially_scanned(obj_to_push, cur)) {
+assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
+obj_to_push = cur;
+}
+bool ok = queue->push(obj_to_push);
+assert(ok, "Should have succeeded");
+}
+assert(young_gen()->overflow_list() == NULL, "Error");
+return num_take_elems > 0;  // was something transferred?
+}
+void ParScanThreadState::push_on_overflow_stack(oop p) {
+assert(UseCompressedOops, "Else should not call");
+overflow_stack()->push(p);
+assert(young_gen()->overflow_list() == NULL, "Error");
 }
 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
 // Otherwise, if the object is small enough, try to reallocate the
 // Since this is being done in a separate thread, need new resource
 // and handle marks.
 ResourceMark rm;
 HandleMark hm;
 // We would need multiple old-gen queues otherwise.
-guarantee(gch->n_gens() == 2,
+assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen.");
-"Par young collection currently only works with one older gen.");
 Generation* old_gen = gch->next_gen(_gen);
 ParScanThreadState& par_scan_state = _state_set->thread_sate(i);
 par_scan_state.set_young_old_boundary(_young_old_boundary);
 return false;
 }
 }
 #endif
+// In case we are using compressed oops, we need to be careful.
+// If the object being pushed is an object array, then its length
+// field keeps track of the "grey boundary" at which the next
+// incremental scan will be done (see ParGCArrayScanChunk).
+// When using compressed oops, this length field is kept in the
+// lower 32 bits of the erstwhile klass word and cannot be used
+// for the overflow chaining pointer (OCP below). As such the OCP
+// would itself need to be compressed into the top 32-bits in this
+// case. Unfortunately, see below, in the event that we have a
+// promotion failure, the node to be pushed on the list can be
+// outside of the Java heap, so the heap-based pointer compression
+// would not work (we would have potential aliasing between C-heap
+// and Java-heap pointers). For this reason, when using compressed
+// oops, we simply use a worker-thread-local, non-shared overflow
+// list in the form of a growable array, with a slightly different
+// overflow stack draining strategy. If/when we start using fat
+// stacks here, we can go back to using (fat) pointer chains
+// (although some performance comparisons would be useful since
+// single global lists have their own performance disadvantages
+// as we were made painfully aware not long ago, see 6786503).
 #define BUSY (oop(0x1aff1aff))
 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
-// if the object has been forwarded to itself, then we cannot
+assert(is_in_reserved(from_space_obj), "Should be from this generation");
-// use the klass pointer for the linked list.  Instead we have
+if (UseCompressedOops) {
-// to allocate an oopDesc in the C-Heap and use that for the linked list.
+// In the case of compressed oops, we use a private, not-shared
-// XXX This is horribly inefficient when a promotion failure occurs
+// overflow stack.
-// and should be fixed. XXX FIX ME !!!
+par_scan_state->push_on_overflow_stack(from_space_obj);
+} else {
+// if the object has been forwarded to itself, then we cannot
+// use the klass pointer for the linked list.  Instead we have
+// to allocate an oopDesc in the C-Heap and use that for the linked list.
+// XXX This is horribly inefficient when a promotion failure occurs
+// and should be fixed. XXX FIX ME !!!
 #ifndef PRODUCT
 Atomic::inc_ptr(&_num_par_pushes);
 assert(_num_par_pushes > 0, "Tautology");
 #endif
 if (from_space_obj->forwardee() == from_space_obj) {
 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1);
 listhead->forward_to(from_space_obj);
 from_space_obj = listhead;
 }
 oop observed_overflow_list = _overflow_list;
 oop cur_overflow_list;
 do {
 cur_overflow_list = observed_overflow_list;
 if (cur_overflow_list != BUSY) {
 from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
 } else {
 from_space_obj->set_klass_to_list_ptr(NULL);
 }
 observed_overflow_list =
 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
 } while (cur_overflow_list != observed_overflow_list);
 }
+}
+bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
+bool res;
+if (UseCompressedOops) {
+res = par_scan_state->take_from_overflow_stack();
+} else {
+res = take_from_overflow_list_work(par_scan_state);
+}
+return res;
+}
 // *NOTE*: The overflow list manipulation code here and
 // in CMSCollector:: are very similar in shape,
 // except that in the CMS case we thread the objects
 // directly into the list via their mark word, and do
 // Because of the common code, if you make any changes in
 // the code below, please check the CMS version to see if
 // similar changes might be needed.
 // See CMSCollector::par_take_from_overflow_list() for
 // more extensive documentation comments.
-bool
+bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
-ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
 ObjToScanQueue* work_q = par_scan_state->work_queue();
-assert(work_q->size() == 0, "Should first empty local work queue");
 // How many to take?
-size_t objsFromOverflow = MIN2((size_t)work_q->max_elems()/4,
+size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
 (size_t)ParGCDesiredObjsFromOverflowList);
+assert(par_scan_state->overflow_stack() == NULL, "Error");
 if (_overflow_list == NULL) return false;
 // Otherwise, there was something there; try claiming the list.
 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
 // Trim off a prefix of at most objsFromOverflow items

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comparison src/share/vm/gc_implementation/parNew/parNewGeneration.cpp @ 679:cea947c8a988