8270187: G1: Remove ConcGCThreads constraint

Reviewed-by: kbarrett, iwalulya

Author: albertnetymk

src/hotspot/share/gc/g1/g1ConcurrentMark.cpp

@@ -377,7 +377,7 @@ G1ConcurrentMark::G1ConcurrentMark(G1CollectedHeap* g1h,
   // _finger set in set_non_marking_state
 
   _worker_id_offset(G1DirtyCardQueueSet::num_par_ids() + G1ConcRefinementThreads),
-  _max_num_tasks(ParallelGCThreads),
+  _max_num_tasks(MAX2(ConcGCThreads, ParallelGCThreads)),
   // _num_active_tasks set in set_non_marking_state()
   // _tasks set inside the constructor
 

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

@@ -148,7 +148,6 @@
                                                                             \
   product(uint, ConcGCThreads, 0,                                           \
           "Number of threads concurrent gc will use")                       \
-          constraint(ConcGCThreadsConstraintFunc,AfterErgo)                 \
                                                                             \
   product(bool, AlwaysTenure, false,                                        \
           "Always tenure objects in eden (ParallelGC only)")                \

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

@@ -67,21 +67,6 @@ JVMFlag::Error ParallelGCThreadsConstraintFunc(uint value, bool verbose) {
   return status;
 }
 
-// As ConcGCThreads should be smaller than ParallelGCThreads,
-// we need constraint function.
-JVMFlag::Error ConcGCThreadsConstraintFunc(uint value, bool verbose) {
-  // G1 GC use ConcGCThreads.
-  if (GCConfig::is_gc_selected(CollectedHeap::G1) && (value > ParallelGCThreads)) {
-    JVMFlag::printError(verbose,
-                        "ConcGCThreads (" UINT32_FORMAT ") must be "
-                        "less than or equal to ParallelGCThreads (" UINT32_FORMAT ")\n",
-                        value, ParallelGCThreads);
-    return JVMFlag::VIOLATES_CONSTRAINT;
-  }
-
-  return JVMFlag::SUCCESS;
-}
-
 static JVMFlag::Error MinPLABSizeBounds(const char* name, size_t value, bool verbose) {
   if ((GCConfig::is_gc_selected(CollectedHeap::G1) || GCConfig::is_gc_selected(CollectedHeap::Parallel)) &&
       (value < PLAB::min_size())) {

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

@@ -42,7 +42,6 @@
  */
 #define SHARED_GC_CONSTRAINTS(f)                               \
  f(uint,   ParallelGCThreadsConstraintFunc)                    \
- f(uint,   ConcGCThreadsConstraintFunc)                        \
  f(size_t, YoungPLABSizeConstraintFunc)                        \
  f(size_t, OldPLABSizeConstraintFunc)                          \
  f(uintx,  MinHeapFreeRatioConstraintFunc)                     \

test/hotspot/jtreg/gc/g1/TestMarkStackSizes.java

@@ -81,7 +81,7 @@ public static void main(String[] args) throws Exception {
 
         runTest(true, "-XX:ConcGCThreads=3", "-XX:ParallelGCThreads=3");
         runTest(true, "-XX:ConcGCThreads=0", "-XX:ParallelGCThreads=3");
-        runTest(false, "-XX:ConcGCThreads=4", "-XX:ParallelGCThreads=3");
+        runTest(true, "-XX:ConcGCThreads=4", "-XX:ParallelGCThreads=3");
 
         // With that high ParallelGCThreads the default ergonomics would calculate
         // a mark stack size higher than maximum mark stack size.