8022800: Use specific generations rather than generation iteration

Reviewed-by: jmasa, ehelin

src/share/vm/gc_implementation/parNew/parNewGeneration.cpp

@@ -927,11 +927,9 @@ void ParNewGeneration::collect(bool   full,
                                    workers->active_workers(),
                                    Threads::number_of_non_daemon_threads());
   workers->set_active_workers(active_workers);
-  _next_gen = gch->next_gen(this);
-  assert(_next_gen != NULL,
-    "This must be the youngest gen, and not the only gen");
   assert(gch->n_gens() == 2,
          "Par collection currently only works with single older gen.");
+  _next_gen = gch->next_gen(this);
   // Do we have to avoid promotion_undo?
   if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) {
     set_avoid_promotion_undo(true);

src/share/vm/memory/cardTableRS.cpp

@@ -321,35 +321,25 @@ void CardTableRS::clear_into_younger(Generation* gen) {
   // below to avoid missing cards at the fringes. If clear() or
   // invalidate() are changed in the future, this code should
   // be revisited. 20040107.ysr
-  Generation* g = gen;
-  for(Generation* prev_gen = gch->prev_gen(g);
-      prev_gen != NULL;
-      g = prev_gen, prev_gen = gch->prev_gen(g)) {
-    MemRegion to_be_cleared_mr = g->prev_used_region();
-    clear(to_be_cleared_mr);
-  }
+  Generation* old_gen = gen;
+  clear(old_gen->prev_used_region());
+  Generation* young_gen = gch->prev_gen(old_gen);
+  clear(young_gen->prev_used_region());
 }
 
-void CardTableRS::invalidate_or_clear(Generation* gen, bool younger) {
-  GenCollectedHeap* gch = GenCollectedHeap::heap();
-  // For each generation gen (and younger)
-  // invalidate the cards for the currently occupied part
-  // of that generation and clear the cards for the
+void CardTableRS::invalidate_or_clear(Generation* gen) {
+  // For generation gen invalidate the cards for the currently
+  // occupied part of that generation and clear the cards for the
   // unoccupied part of the generation (if any, making use
   // of that generation's prev_used_region to determine that
   // region). No need to do anything for the youngest
   // generation. Also see note#20040107.ysr above.
-  Generation* g = gen;
-  for(Generation* prev_gen = gch->prev_gen(g); prev_gen != NULL;
-      g = prev_gen, prev_gen = gch->prev_gen(g))  {
-    MemRegion used_mr = g->used_region();
-    MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);
+  MemRegion used_mr = gen->used_region();
+  MemRegion to_be_cleared_mr = gen->prev_used_region().minus(used_mr);
   if (!to_be_cleared_mr.is_empty()) {
     clear(to_be_cleared_mr);
   }
   invalidate(used_mr);
-    if (!younger) break;
-  }
 }
 
 

src/share/vm/memory/cardTableRS.hpp

@@ -147,7 +147,7 @@ public:
   void invalidate(MemRegion mr, bool whole_heap = false) {
     _ct_bs->invalidate(mr, whole_heap);
   }
-  void invalidate_or_clear(Generation* gen, bool younger);
+  void invalidate_or_clear(Generation* gen);
 
   static uintx ct_max_alignment_constraint() {
     return CardTableModRefBS::ct_max_alignment_constraint();

src/share/vm/memory/defNewGeneration.cpp

@@ -567,8 +567,6 @@ void DefNewGeneration::collect(bool   full,
   gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
 
   _next_gen = gch->next_gen(this);
-  assert(_next_gen != NULL,
-    "This must be the youngest gen, and not the only gen");
 
   // If the next generation is too full to accommodate promotion
   // from this generation, pass on collection; let the next generation
@@ -901,8 +899,6 @@ bool DefNewGeneration::collection_attempt_is_safe() {
   if (_next_gen == NULL) {
     GenCollectedHeap* gch = GenCollectedHeap::heap();
     _next_gen = gch->next_gen(this);
-    assert(_next_gen != NULL,
-           "This must be the youngest gen, and not the only gen");
   }
   return _next_gen->promotion_attempt_is_safe(used());
 }

src/share/vm/memory/genCollectedHeap.cpp

@@ -1070,13 +1070,13 @@ GenCollectedHeap* GenCollectedHeap::heap() {
 
 
 void GenCollectedHeap::prepare_for_compaction() {
-  Generation* scanning_gen = _gens[_n_gens-1];
+  guarantee(_n_gens = 2, "Wrong number of generations");
+  Generation* old_gen = _gens[1];
   // Start by compacting into same gen.
-  CompactPoint cp(scanning_gen, NULL, NULL);
-  while (scanning_gen != NULL) {
-    scanning_gen->prepare_for_compaction(&cp);
-    scanning_gen = prev_gen(scanning_gen);
-  }
+  CompactPoint cp(old_gen, NULL, NULL);
+  old_gen->prepare_for_compaction(&cp);
+  Generation* young_gen = _gens[0];
+  young_gen->prepare_for_compaction(&cp);
 }
 
 GCStats* GenCollectedHeap::gc_stats(int level) const {
@@ -1245,27 +1245,14 @@ void GenCollectedHeap::ensure_parsability(bool retire_tlabs) {
   generation_iterate(&ep_cl, false);
 }
 
-oop GenCollectedHeap::handle_failed_promotion(Generation* gen,
+oop GenCollectedHeap::handle_failed_promotion(Generation* old_gen,
                                               oop obj,
                                               size_t obj_size) {
+  guarantee(old_gen->level() == 1, "We only get here with an old generation");
   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
   HeapWord* result = NULL;
 
-  // First give each higher generation a chance to allocate the promoted object.
-  Generation* allocator = next_gen(gen);
-  if (allocator != NULL) {
-    do {
-      result = allocator->allocate(obj_size, false);
-    } while (result == NULL && (allocator = next_gen(allocator)) != NULL);
-  }
-
-  if (result == NULL) {
-    // Then give gen and higher generations a chance to expand and allocate the
-    // object.
-    do {
-      result = gen->expand_and_allocate(obj_size, false);
-    } while (result == NULL && (gen = next_gen(gen)) != NULL);
-  }
+  result = old_gen->expand_and_allocate(obj_size, false);
 
   if (result != NULL) {
     Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size);

src/share/vm/memory/genCollectedHeap.hpp

@@ -368,25 +368,23 @@ public:
   // collection.
   virtual bool is_maximal_no_gc() const;
 
-  // Return the generation before "gen", or else NULL.
+  // Return the generation before "gen".
   Generation* prev_gen(Generation* gen) const {
     int l = gen->level();
-    if (l == 0) return NULL;
-    else return _gens[l-1];
+    guarantee(l > 0, "Out of bounds");
+    return _gens[l-1];
   }
 
-  // Return the generation after "gen", or else NULL.
+  // Return the generation after "gen".
   Generation* next_gen(Generation* gen) const {
     int l = gen->level() + 1;
-    if (l == _n_gens) return NULL;
-    else return _gens[l];
+    guarantee(l < _n_gens, "Out of bounds");
+    return _gens[l];
   }
 
   Generation* get_gen(int i) const {
-    if (i >= 0 && i < _n_gens)
+    guarantee(i >= 0 && i < _n_gens, "Out of bounds");
     return _gens[i];
-    else
-      return NULL;
   }
 
   int n_gens() const {
@@ -485,9 +483,9 @@ public:
 
   // Promotion of obj into gen failed.  Try to promote obj to higher
   // gens in ascending order; return the new location of obj if successful.
-  // Otherwise, try expand-and-allocate for obj in each generation starting at
-  // gen; return the new location of obj if successful.  Otherwise, return NULL.
-  oop handle_failed_promotion(Generation* gen,
+  // Otherwise, try expand-and-allocate for obj in both the young and old
+  // generation; return the new location of obj if successful.  Otherwise, return NULL.
+  oop handle_failed_promotion(Generation* old_gen,
                               oop obj,
                               size_t obj_size);
 

src/share/vm/memory/genMarkSweep.cpp

@@ -52,8 +52,8 @@
 #include "utilities/copy.hpp"
 #include "utilities/events.hpp"
 
-void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
-  bool clear_all_softrefs) {
+void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp, bool clear_all_softrefs) {
+  guarantee(level == 1, "We always collect both old and young.");
   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 
   GenCollectedHeap* gch = GenCollectedHeap::heap();
@@ -84,11 +84,6 @@ void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
   // Capture heap size before collection for printing.
   size_t gch_prev_used = gch->used();
 
-  // Some of the card table updates below assume that the perm gen is
-  // also being collected.
-  assert(level == gch->n_gens() - 1,
-         "All generations are being collected, ergo perm gen too.");
-
   // Capture used regions for each generation that will be
   // subject to collection, so that card table adjustments can
   // be made intelligently (see clear / invalidate further below).
@@ -134,9 +129,9 @@ void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
   } else {
     // Invalidate the cards corresponding to the currently used
     // region and clear those corresponding to the evacuated region
-    // of all generations just collected (i.e. level and younger).
-    rs->invalidate_or_clear(gch->get_gen(level),
-                            true /* younger */);
+    // of all generations just collected.
+    rs->invalidate_or_clear(gch->get_gen(1));
+    rs->invalidate_or_clear(gch->get_gen(0));
   }
 
   Threads::gc_epilogue();

src/share/vm/memory/genRemSet.hpp

@@ -146,11 +146,8 @@ public:
 
   // Informs the RS that refs in this generation
   // may have changed arbitrarily, and therefore may contain
-  // old-to-young pointers in arbitrary locations. The parameter
-  // younger indicates if the same should be done for younger generations
-  // as well. The parameter perm indicates if the same should be done for
-  // perm gen as well.
-  virtual void invalidate_or_clear(Generation* gen, bool younger) = 0;
+  // old-to-young pointers in arbitrary locations.
+  virtual void invalidate_or_clear(Generation* gen) = 0;
 };
 
 #endif // SHARE_VM_MEMORY_GENREMSET_HPP