# HG changeset patch
# User vkempik
# Date 1413298339 -14400
# Node ID 6b27e1adb4bd5d90aeb7d71a36535433bed93c49
# Parent  635afc2ed41018373c10ae8fbd43821303371dc6
8055479: TLAB stability
Reviewed-by: mgerdin

diff -r 635afc2ed410 -r 6b27e1adb4bd src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
--- a/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp	Mon Oct 13 12:12:07 2014 -0700
+++ b/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp	Tue Oct 14 18:52:19 2014 +0400
@@ -757,7 +757,7 @@
   // Support for parallelizing survivor space rescan
   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
     const size_t max_plab_samples =
-      ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
+      ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
 
     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
@@ -824,6 +824,12 @@
   _inter_sweep_timer.start();  // start of time
 }
 
+size_t CMSCollector::plab_sample_minimum_size() {
+  // The default value of MinTLABSize is 2k, but there is
+  // no way to get the default value if the flag has been overridden.
+  return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
+}
+
 const char* ConcurrentMarkSweepGeneration::name() const {
   return "concurrent mark-sweep generation";
 }
diff -r 635afc2ed410 -r 6b27e1adb4bd src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp
--- a/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp	Mon Oct 13 12:12:07 2014 -0700
+++ b/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp	Tue Oct 14 18:52:19 2014 +0400
@@ -766,6 +766,10 @@
   size_t*    _cursor;
   ChunkArray* _survivor_plab_array;
 
+  // A bounded minimum size of PLABs, should not return too small values since
+  // this will affect the size of the data structures used for parallel young gen rescan
+  size_t plab_sample_minimum_size();
+
   // Support for marking stack overflow handling
   bool take_from_overflow_list(size_t num, CMSMarkStack* to_stack);
   bool par_take_from_overflow_list(size_t num,
diff -r 635afc2ed410 -r 6b27e1adb4bd src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp
--- a/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp	Mon Oct 13 12:12:07 2014 -0700
+++ b/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp	Tue Oct 14 18:52:19 2014 +0400
@@ -62,7 +62,8 @@
   ParGCAllocBuffer(size_t word_sz);
 
   static const size_t min_size() {
-    return ThreadLocalAllocBuffer::min_size();
+    // Make sure that we return something that is larger than AlignmentReserve
+    return align_object_size(MAX2(MinTLABSize / HeapWordSize, (uintx)oopDesc::header_size())) + AlignmentReserve;
   }
 
   static const size_t max_size() {
diff -r 635afc2ed410 -r 6b27e1adb4bd src/share/vm/memory/threadLocalAllocBuffer.cpp
--- a/src/share/vm/memory/threadLocalAllocBuffer.cpp	Mon Oct 13 12:12:07 2014 -0700
+++ b/src/share/vm/memory/threadLocalAllocBuffer.cpp	Tue Oct 14 18:52:19 2014 +0400
@@ -240,22 +240,19 @@
 }
 
 size_t ThreadLocalAllocBuffer::initial_desired_size() {
-  size_t init_sz;
+  size_t init_sz = 0;
 
   if (TLABSize > 0) {
-    init_sz = MIN2(TLABSize / HeapWordSize, max_size());
-  } else if (global_stats() == NULL) {
-    // Startup issue - main thread initialized before heap initialized.
-    init_sz = min_size();
-  } else {
+    init_sz = TLABSize / HeapWordSize;
+  } else if (global_stats() != NULL) {
     // Initial size is a function of the average number of allocating threads.
     unsigned nof_threads = global_stats()->allocating_threads_avg();
 
     init_sz  = (Universe::heap()->tlab_capacity(myThread()) / HeapWordSize) /
                       (nof_threads * target_refills());
     init_sz = align_object_size(init_sz);
-    init_sz = MIN2(MAX2(init_sz, min_size()), max_size());
   }
+  init_sz = MIN2(MAX2(init_sz, min_size()), max_size());
   return init_sz;
 }
 
diff -r 635afc2ed410 -r 6b27e1adb4bd src/share/vm/memory/threadLocalAllocBuffer.hpp
--- a/src/share/vm/memory/threadLocalAllocBuffer.hpp	Mon Oct 13 12:12:07 2014 -0700
+++ b/src/share/vm/memory/threadLocalAllocBuffer.hpp	Tue Oct 14 18:52:19 2014 +0400
@@ -103,7 +103,7 @@
     // do nothing.  tlabs must be inited by initialize() calls
   }
 
-  static const size_t min_size()                 { return align_object_size(MinTLABSize / HeapWordSize); }
+  static const size_t min_size()                 { return align_object_size(MinTLABSize / HeapWordSize) + alignment_reserve(); }
   static const size_t max_size();
 
   HeapWord* start() const                        { return _start; }