6883834: ParNew: assert(!_g->to()->is_in_reserved(obj),"Scanning field...

6883834: ParNew: assert(!_g->to()->is_in_reserved(obj),"Scanning field twice?") with LargeObjects tests
Summary: Fixed process_chunk_boundaries(), used for parallel card scanning when using ParNew/CMS, so as to prevent double-scanning, or worse, non-scanning of imprecisely marked objects exceeding parallel chunk size. Made some sizing parameters for parallel card scanning diagnostic, disabled ParallelGCRetainPLAB, and elaborated and clarified some comments.
Reviewed-by: stefank, johnc

src/share/vm/gc_implementation/parNew/parOopClosures.inline.hpp

@@ -77,7 +77,23 @@ inline void ParScanClosure::do_oop_work(T* p,
   if (!oopDesc::is_null(heap_oop)) {
     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
     if ((HeapWord*)obj < _boundary) {
-      assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
+#ifndef PRODUCT
+      if (_g->to()->is_in_reserved(obj)) {
+        tty->print_cr("Scanning field (" PTR_FORMAT ") twice?", p);
+        GenCollectedHeap* gch =  (GenCollectedHeap*)Universe::heap();
+        Space* sp = gch->space_containing(p);
+        oop obj = oop(sp->block_start(p));
+        assert((HeapWord*)obj < (HeapWord*)p, "Error");
+        tty->print_cr("Object: " PTR_FORMAT, obj);
+        tty->print_cr("-------");
+        obj->print();
+        tty->print_cr("-----");
+        tty->print_cr("Heap:");
+        tty->print_cr("-----");
+        gch->print();
+        ShouldNotReachHere();
+      }
+#endif
       // OK, we need to ensure that it is copied.
       // We read the klass and mark in this order, so that we can reliably
       // get the size of the object: if the mark we read is not a

src/share/vm/memory/cardTableModRefBS.cpp

@@ -455,25 +455,29 @@ bool CardTableModRefBS::mark_card_deferred(size_t card_index) {
   return true;
 }
 
-
 void CardTableModRefBS::non_clean_card_iterate_possibly_parallel(Space* sp,
                                                                  MemRegion mr,
-                                                                 DirtyCardToOopClosure* dcto_cl,
-                                                                 ClearNoncleanCardWrapper* cl) {
+                                                                 OopsInGenClosure* cl,
+                                                                 CardTableRS* ct) {
   if (!mr.is_empty()) {
     int n_threads = SharedHeap::heap()->n_par_threads();
     if (n_threads > 0) {
 #ifndef SERIALGC
-      non_clean_card_iterate_parallel_work(sp, mr, dcto_cl, cl, n_threads);
+      non_clean_card_iterate_parallel_work(sp, mr, cl, ct, n_threads);
 #else  // SERIALGC
       fatal("Parallel gc not supported here.");
 #endif // SERIALGC
     } else {
       // We do not call the non_clean_card_iterate_serial() version below because
       // we want to clear the cards (which non_clean_card_iterate_serial() does not
-      // do for us), and the ClearNoncleanCardWrapper closure itself does the work
-      // of finding contiguous dirty ranges of cards to process (and clear).
-      cl->do_MemRegion(mr);
+      // do for us): clear_cl here does the work of finding contiguous dirty ranges
+      // of cards to process and clear.
+
+      DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(),
+                                                       cl->gen_boundary());
+      ClearNoncleanCardWrapper clear_cl(dcto_cl, ct);
+
+      clear_cl.do_MemRegion(mr);
     }
   }
 }

src/share/vm/memory/cardTableModRefBS.hpp

@@ -173,18 +173,17 @@ class CardTableModRefBS: public ModRefBarrierSet {
   // A variant of the above that will operate in a parallel mode if
   // worker threads are available, and clear the dirty cards as it
   // processes them.
-  // ClearNoncleanCardWrapper cl must wrap the DirtyCardToOopClosure dcto_cl,
-  // which may itself be modified by the method.
+  // XXX ??? MemRegionClosure above vs OopsInGenClosure below XXX
+  // XXX some new_dcto_cl's take OopClosure's, plus as above there are
+  // some MemRegionClosures. Clean this up everywhere. XXX
   void non_clean_card_iterate_possibly_parallel(Space* sp, MemRegion mr,
-                                                DirtyCardToOopClosure* dcto_cl,
-                                                ClearNoncleanCardWrapper* cl);
+                                                OopsInGenClosure* cl, CardTableRS* ct);
 
  private:
   // Work method used to implement non_clean_card_iterate_possibly_parallel()
   // above in the parallel case.
   void non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
-                                            DirtyCardToOopClosure* dcto_cl,
-                                            ClearNoncleanCardWrapper* cl,
+                                            OopsInGenClosure* cl, CardTableRS* ct,
                                             int n_threads);
 
  protected:
@@ -198,11 +197,6 @@ class CardTableModRefBS: public ModRefBarrierSet {
 
   // *** Support for parallel card scanning.
 
-  enum SomeConstantsForParallelism {
-    StridesPerThread    = 2,
-    CardsPerStrideChunk = 256
-  };
-
   // This is an array, one element per covered region of the card table.
   // Each entry is itself an array, with one element per chunk in the
   // covered region.  Each entry of these arrays is the lowest non-clean
@@ -235,7 +229,7 @@ class CardTableModRefBS: public ModRefBarrierSet {
   // covers the given address.
   uintptr_t addr_to_chunk_index(const void* addr) {
     uintptr_t card = (uintptr_t) byte_for(addr);
-    return card / CardsPerStrideChunk;
+    return card / ParGCCardsPerStrideChunk;
   }
 
   // Apply cl, which must either itself apply dcto_cl or be dcto_cl,
@@ -243,8 +237,8 @@ class CardTableModRefBS: public ModRefBarrierSet {
   void process_stride(Space* sp,
                       MemRegion used,
                       jint stride, int n_strides,
-                      DirtyCardToOopClosure* dcto_cl,
-                      ClearNoncleanCardWrapper* cl,
+                      OopsInGenClosure* cl,
+                      CardTableRS* ct,
                       jbyte** lowest_non_clean,
                       uintptr_t lowest_non_clean_base_chunk_index,
                       size_t lowest_non_clean_chunk_size);
@@ -482,7 +476,7 @@ public:
   void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
 
   static size_t par_chunk_heapword_alignment() {
-    return CardsPerStrideChunk * card_size_in_words;
+    return ParGCCardsPerStrideChunk * card_size_in_words;
   }
 
 };

src/share/vm/memory/cardTableRS.cpp

@@ -162,7 +162,7 @@ inline bool ClearNoncleanCardWrapper::clear_card_serial(jbyte* entry) {
 }
 
 ClearNoncleanCardWrapper::ClearNoncleanCardWrapper(
-  MemRegionClosure* dirty_card_closure, CardTableRS* ct) :
+  DirtyCardToOopClosure* dirty_card_closure, CardTableRS* ct) :
     _dirty_card_closure(dirty_card_closure), _ct(ct) {
     _is_par = (SharedHeap::heap()->n_par_threads() > 0);
 }
@@ -246,10 +246,6 @@ void CardTableRS::write_ref_field_gc_par(void* field, oop new_val) {
 
 void CardTableRS::younger_refs_in_space_iterate(Space* sp,
                                                 OopsInGenClosure* cl) {
-  DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, _ct_bs->precision(),
-                                                   cl->gen_boundary());
-  ClearNoncleanCardWrapper clear_cl(dcto_cl, this);
-
   const MemRegion urasm = sp->used_region_at_save_marks();
 #ifdef ASSERT
   // Convert the assertion check to a warning if we are running
@@ -275,10 +271,10 @@ void CardTableRS::younger_refs_in_space_iterate(Space* sp,
     if (!urasm.equals(urasm2)) {
       warning("CMS+ParNew: Flickering used_region_at_save_marks()!!");
     }
+    ShouldNotReachHere();
   }
 #endif
-  _ct_bs->non_clean_card_iterate_possibly_parallel(sp, urasm,
-                                                   dcto_cl, &clear_cl);
+  _ct_bs->non_clean_card_iterate_possibly_parallel(sp, urasm, cl, this);
 }
 
 void CardTableRS::clear_into_younger(Generation* gen, bool clear_perm) {

src/share/vm/memory/cardTableRS.hpp

@@ -31,7 +31,6 @@
 
 class Space;
 class OopsInGenClosure;
-class DirtyCardToOopClosure;
 
 // This kind of "GenRemSet" uses a card table both as shared data structure
 // for a mod ref barrier set and for the rem set information.
@@ -167,7 +166,7 @@ public:
 };
 
 class ClearNoncleanCardWrapper: public MemRegionClosure {
-  MemRegionClosure* _dirty_card_closure;
+  DirtyCardToOopClosure* _dirty_card_closure;
   CardTableRS* _ct;
   bool _is_par;
 private:
@@ -179,7 +178,7 @@ private:
   inline bool clear_card_parallel(jbyte* entry);
 
 public:
-  ClearNoncleanCardWrapper(MemRegionClosure* dirty_card_closure, CardTableRS* ct);
+  ClearNoncleanCardWrapper(DirtyCardToOopClosure* dirty_card_closure, CardTableRS* ct);
   void do_MemRegion(MemRegion mr);
 };
 

src/share/vm/memory/space.cpp

@@ -97,6 +97,14 @@ void DirtyCardToOopClosure::walk_mem_region(MemRegion mr,
   }
 }
 
+// We get called with "mr" representing the dirty region
+// that we want to process. Because of imprecise marking,
+// we may need to extend the incoming "mr" to the right,
+// and scan more. However, because we may already have
+// scanned some of that extended region, we may need to
+// trim its right-end back some so we do not scan what
+// we (or another worker thread) may already have scanned
+// or planning to scan.
 void DirtyCardToOopClosure::do_MemRegion(MemRegion mr) {
 
   // Some collectors need to do special things whenever their dirty
@@ -148,7 +156,7 @@ void DirtyCardToOopClosure::do_MemRegion(MemRegion mr) {
   // e.g. the dirty card region is entirely in a now free object
   // -- something that could happen with a concurrent sweeper.
   bottom = MIN2(bottom, top);
-  mr     = MemRegion(bottom, top);
+  MemRegion extended_mr = MemRegion(bottom, top);
   assert(bottom <= top &&
          (_precision != CardTableModRefBS::ObjHeadPreciseArray ||
           _min_done == NULL ||
@@ -156,8 +164,8 @@ void DirtyCardToOopClosure::do_MemRegion(MemRegion mr) {
          "overlap!");
 
   // Walk the region if it is not empty; otherwise there is nothing to do.
-  if (!mr.is_empty()) {
-    walk_mem_region(mr, bottom_obj, top);
+  if (!extended_mr.is_empty()) {
+    walk_mem_region(extended_mr, bottom_obj, top);
   }
 
   // An idempotent closure might be applied in any order, so we don't

src/share/vm/runtime/globals.hpp

@@ -1460,8 +1460,10 @@ class CommandLineFlags {
   product(intx, ParallelGCBufferWastePct, 10,                               \
           "wasted fraction of parallel allocation buffer.")                 \
                                                                             \
-  product(bool, ParallelGCRetainPLAB, true,                                 \
-          "Retain parallel allocation buffers across scavenges.")           \
+  diagnostic(bool, ParallelGCRetainPLAB, false,                             \
+             "Retain parallel allocation buffers across scavenges; "        \
+             " -- disabled because this currently conflicts with "          \
+             " parallel card scanning under certain conditions ")           \
                                                                             \
   product(intx, TargetPLABWastePct, 10,                                     \
           "target wasted space in last buffer as pct of overall allocation")\
@@ -1495,7 +1497,15 @@ class CommandLineFlags {
   product(uintx, ParGCDesiredObjsFromOverflowList, 20,                      \
           "The desired number of objects to claim from the overflow list")  \
                                                                             \
-  product(uintx, CMSParPromoteBlocksToClaim, 16,                             \
+  diagnostic(intx, ParGCStridesPerThread, 2,                                \
+          "The number of strides per worker thread that we divide up the "  \
+          "card table scanning work into")                                  \
+                                                                            \
+  diagnostic(intx, ParGCCardsPerStrideChunk, 256,                           \
+          "The number of cards in each chunk of the parallel chunks used "  \
+          "during card table scanning")                                     \
+                                                                            \
+  product(uintx, CMSParPromoteBlocksToClaim, 16,                            \
           "Number of blocks to attempt to claim when refilling CMS LAB for "\
           "parallel GC.")                                                   \
                                                                             \