8371643: Remove ThreadLocalAllocBuffer::_reserve_for_allocation_prefetch

src/hotspot/share/gc/shared/threadLocalAllocBuffer.cpp

@@ -37,7 +37,6 @@
 #include "utilities/copy.hpp"
 
 size_t       ThreadLocalAllocBuffer::_max_size = 0;
-int          ThreadLocalAllocBuffer::_reserve_for_allocation_prefetch = 0;
 unsigned int ThreadLocalAllocBuffer::_target_refills = 0;
 
 ThreadLocalAllocBuffer::ThreadLocalAllocBuffer() :
@@ -225,30 +224,6 @@ void ThreadLocalAllocBuffer::startup_initialization() {
   // abort during VM initialization.
   _target_refills = MAX2(_target_refills, 2U);
 
-#ifdef COMPILER2
-  // If the C2 compiler is present, extra space is needed at the end of
-  // TLABs, otherwise prefetching instructions generated by the C2
-  // compiler will fault (due to accessing memory outside of heap).
-  // The amount of space is the max of the number of lines to
-  // prefetch for array and for instance allocations. (Extra space must be
-  // reserved to accommodate both types of allocations.)
-  //
-  // Only SPARC-specific BIS instructions are known to fault. (Those
-  // instructions are generated if AllocatePrefetchStyle==3 and
-  // AllocatePrefetchInstr==1). To be on the safe side, however,
-  // extra space is reserved for all combinations of
-  // AllocatePrefetchStyle and AllocatePrefetchInstr.
-  //
-  // If the C2 compiler is not present, no space is reserved.
-
-  // +1 for rounding up to next cache line, +1 to be safe
-  if (CompilerConfig::is_c2_or_jvmci_compiler_enabled()) {
-    int lines =  MAX2(AllocatePrefetchLines, AllocateInstancePrefetchLines) + 2;
-    _reserve_for_allocation_prefetch = (AllocatePrefetchDistance + AllocatePrefetchStepSize * lines) /
-                                       (int)HeapWordSize;
-  }
-#endif
-
   // During jvm startup, the main thread is initialized
   // before the heap is initialized.  So reinitialize it now.
   guarantee(Thread::current()->is_Java_thread(), "tlab initialization thread not Java thread");
@@ -454,8 +429,7 @@ void ThreadLocalAllocStats::publish() {
 }
 
 size_t ThreadLocalAllocBuffer::end_reserve() {
-  size_t reserve_size = CollectedHeap::lab_alignment_reserve();
-  return MAX2(reserve_size, (size_t)_reserve_for_allocation_prefetch);
+  return CollectedHeap::lab_alignment_reserve();
 }
 
 const HeapWord* ThreadLocalAllocBuffer::start_relaxed() const {

src/hotspot/share/gc/shared/threadLocalAllocBuffer.hpp

@@ -58,7 +58,6 @@ class ThreadLocalAllocBuffer: public CHeapObj<mtThread> {
   size_t    _allocated_before_last_gc;           // total bytes allocated up until the last gc
 
   static size_t   _max_size;                          // maximum size of any TLAB
-  static int      _reserve_for_allocation_prefetch;   // Reserve at the end of the TLAB
   static unsigned _target_refills;                    // expected number of refills between GCs
 
   unsigned  _number_of_refills;

src/hotspot/share/runtime/vmStructs.cpp

@@ -350,7 +350,6 @@
   nonstatic_field(ThreadLocalAllocBuffer,      _pf_top,                                       HeapWord*)                             \
   nonstatic_field(ThreadLocalAllocBuffer,      _desired_size,                                 size_t)                                \
   nonstatic_field(ThreadLocalAllocBuffer,      _refill_waste_limit,                           size_t)                                \
-     static_field(ThreadLocalAllocBuffer,      _reserve_for_allocation_prefetch,              int)                                   \
      static_field(ThreadLocalAllocBuffer,      _target_refills,                               unsigned)                              \
   nonstatic_field(ThreadLocalAllocBuffer,      _number_of_refills,                            unsigned)                              \
   nonstatic_field(ThreadLocalAllocBuffer,      _refill_waste,                                 unsigned)                              \

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/ThreadLocalAllocBuffer.java

@@ -76,10 +76,9 @@ private long alignmentReserve() {
 
   private long endReserve() {
     long labAlignmentReserve = VM.getVM().getLabAlignmentReserve();
-    long reserveForAllocationPrefetch = VM.getVM().getReserveForAllocationPrefetch();
     long heapWordSize = VM.getVM().getHeapWordSize();
 
-    return Math.max(labAlignmentReserve, reserveForAllocationPrefetch) * heapWordSize;
+    return labAlignmentReserve * heapWordSize;
   }
 
   /** Support for iteration over heap -- not sure how this will

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/VM.java

@@ -123,7 +123,6 @@ public class VM {
   private int          invocationEntryBCI;
   private ReversePtrs  revPtrs;
   private VMRegImpl    vmregImpl;
-  private int          reserveForAllocationPrefetch;
   private int          labAlignmentReserve;
 
   // System.getProperties from debuggee VM
@@ -447,8 +446,6 @@ private VM(TypeDataBase db, JVMDebugger debugger, boolean isBigEndian) {
     boolType = (CIntegerType) db.lookupType("bool");
 
     Type threadLocalAllocBuffer = db.lookupType("ThreadLocalAllocBuffer");
-    CIntegerField reserveForAllocationPrefetchField = threadLocalAllocBuffer.getCIntegerField("_reserve_for_allocation_prefetch");
-    reserveForAllocationPrefetch = (int)reserveForAllocationPrefetchField.getCInteger(intType);
 
     Type collectedHeap = db.lookupType("CollectedHeap");
     CIntegerField labAlignmentReserveField = collectedHeap.getCIntegerField("_lab_alignment_reserve");
@@ -915,10 +912,6 @@ public String getVMInternalInfo() {
     return vmInternalInfo;
   }
 
-  public int getReserveForAllocationPrefetch() {
-    return reserveForAllocationPrefetch;
-  }
-
   public int getLabAlignmentReserve() {
     return labAlignmentReserve;
   }