8330670: Obsolete ScavengeBeforeFullGC

Reviewed-by: stefank, tschatzl

src/hotspot/share/gc/parallel/psParallelCompact.cpp

@@ -1273,10 +1273,6 @@ bool PSParallelCompact::invoke(bool maximum_heap_compaction) {
 
   IsGCActiveMark mark;
 
-  if (ScavengeBeforeFullGC) {
-    PSScavenge::invoke_no_policy();
-  }
-
   const bool clear_all_soft_refs =
     heap->soft_ref_policy()->should_clear_all_soft_refs();
 

src/hotspot/share/gc/serial/serialHeap.cpp

@@ -498,7 +498,7 @@ void SerialHeap::do_collection(bool full,
   IsGCActiveMark active_gc_mark;
 
   bool complete = full && (max_generation == OldGen);
-  bool old_collects_young = complete && !ScavengeBeforeFullGC;
+  bool old_collects_young = complete;
   bool do_young_collection = !old_collects_young && _young_gen->should_collect(full, size, is_tlab);
 
   const PreGenGCValues pre_gc_values = get_pre_gc_values();

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

@@ -40,10 +40,6 @@ void GCArguments::initialize() {
     MarkSweepAlwaysCompactCount = 1;  // Move objects every gc.
   }
 
-  if (!UseParallelGC && FLAG_IS_DEFAULT(ScavengeBeforeFullGC)) {
-    FLAG_SET_DEFAULT(ScavengeBeforeFullGC, false);
-  }
-
   if (GCTimeLimit == 100) {
     // Turn off gc-overhead-limit-exceeded checks
     FLAG_SET_DEFAULT(UseGCOverheadLimit, false);

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

@@ -154,9 +154,6 @@
           "Never tenure objects in eden, may tenure on overflow "           \
           "(ParallelGC only)")                                              \
                                                                             \
-  product(bool, ScavengeBeforeFullGC, true,                                 \
-          "Scavenge youngest generation before each full GC.")              \
-                                                                            \
   product(bool, ExplicitGCInvokesConcurrent, false,                         \
           "A System.gc() request invokes a concurrent collection; "         \
           "(effective only when using concurrent collectors)")              \

src/hotspot/share/gc/z/zDriver.cpp

@@ -310,8 +310,7 @@ static bool should_preclean_young(GCCause::Cause cause) {
   // catch that above and perform young gen pre-cleaning.
   assert(!should_clear_soft_references(cause), "Clearing soft references without pre-cleaning young gen");
 
-  // Preclean young if implied by configuration
+  return false;
-  return ScavengeBeforeFullGC;
 }
 
 ZDriverMajor::ZDriverMajor()

src/hotspot/share/runtime/arguments.cpp

@@ -541,6 +541,7 @@ static SpecialFlag const special_jvm_flags[] = {
   { "ParallelOldDeadWoodLimiterMean",   JDK_Version::undefined(), JDK_Version::jdk(23), JDK_Version::jdk(24) },
   { "ParallelOldDeadWoodLimiterStdDev", JDK_Version::undefined(), JDK_Version::jdk(23), JDK_Version::jdk(24) },
   { "UseNeon",                      JDK_Version::undefined(), JDK_Version::jdk(23), JDK_Version::jdk(24) },
+  { "ScavengeBeforeFullGC",         JDK_Version::undefined(), JDK_Version::jdk(23), JDK_Version::jdk(24) },
 #ifdef ASSERT
   { "DummyObsoleteTestFlag",        JDK_Version::undefined(), JDK_Version::jdk(18), JDK_Version::undefined() },
 #endif
@@ -1715,11 +1716,6 @@ jint Arguments::set_aggressive_heap_flags() {
     return JNI_EINVAL;
   }
 
-  // This appears to improve mutator locality
-  if (FLAG_SET_CMDLINE(ScavengeBeforeFullGC, false) != JVMFlag::SUCCESS) {
-    return JNI_EINVAL;
-  }
-
   return JNI_OK;
 }
 
@@ -2735,10 +2731,6 @@ jint Arguments::parse_each_vm_init_arg(const JavaVMInitArgs* args, bool* patch_m
       if (FLAG_SET_CMDLINE(FullGCALot, true) != JVMFlag::SUCCESS) {
         return JNI_EINVAL;
       }
-      // disable scavenge before parallel mark-compact
-      if (FLAG_SET_CMDLINE(ScavengeBeforeFullGC, false) != JVMFlag::SUCCESS) {
-        return JNI_EINVAL;
-      }
 #endif
 #if !INCLUDE_MANAGEMENT
     } else if (match_option(option, "-XX:+ManagementServer")) {

test/hotspot/jtreg/vmTestbase/gc/gctests/WeakReference/weak006/weak006.java

@@ -32,7 +32,7 @@
  *          /test/lib
  * @build jdk.test.whitebox.WhiteBox
  * @run driver jdk.test.lib.helpers.ClassFileInstaller jdk.test.whitebox.WhiteBox
- * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -XX:+IgnoreUnrecognizedVMOptions -XX:-ScavengeBeforeFullGC gc.gctests.WeakReference.weak006.weak006 -t 1
+ * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -XX:+IgnoreUnrecognizedVMOptions gc.gctests.WeakReference.weak006.weak006 -t 1
  */
 
 package gc.gctests.WeakReference.weak006;