8270100: Fix some inaccurate GC logging

Reviewed-by: ayang, tschatzl

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

@@ -313,29 +313,31 @@ bool DefNewGeneration::expand(size_t bytes) {
   return success;
 }
 
+size_t DefNewGeneration::calculate_thread_increase_size(int threads_count) const {
+    size_t thread_increase_size = 0;
+    // Check an overflow at 'threads_count * NewSizeThreadIncrease'.
+    if (threads_count > 0 && NewSizeThreadIncrease <= max_uintx / threads_count) {
+      thread_increase_size = threads_count * NewSizeThreadIncrease;
+    }
+    return thread_increase_size;
+}
+
 size_t DefNewGeneration::adjust_for_thread_increase(size_t new_size_candidate,
                                                     size_t new_size_before,
-                                                    size_t alignment) const {
+                                                    size_t alignment,
+                                                    size_t thread_increase_size) const {
   size_t desired_new_size = new_size_before;
 
-  if (NewSizeThreadIncrease > 0) {
-    int threads_count;
-    size_t thread_increase_size = 0;
-
-    // 1. Check an overflow at 'threads_count * NewSizeThreadIncrease'.
-    threads_count = Threads::number_of_non_daemon_threads();
-    if (threads_count > 0 && NewSizeThreadIncrease <= max_uintx / threads_count) {
-      thread_increase_size = threads_count * NewSizeThreadIncrease;
+  if (NewSizeThreadIncrease > 0 && thread_increase_size > 0) {
 
-      // 2. Check an overflow at 'new_size_candidate + thread_increase_size'.
-      if (new_size_candidate <= max_uintx - thread_increase_size) {
-        new_size_candidate += thread_increase_size;
+    // 1. Check an overflow at 'new_size_candidate + thread_increase_size'.
+    if (new_size_candidate <= max_uintx - thread_increase_size) {
+      new_size_candidate += thread_increase_size;
 
-        // 3. Check an overflow at 'align_up'.
-        size_t aligned_max = ((max_uintx - alignment) & ~(alignment-1));
-        if (new_size_candidate <= aligned_max) {
-          desired_new_size = align_up(new_size_candidate, alignment);
-        }
+      // 2. Check an overflow at 'align_up'.
+      size_t aligned_max = ((max_uintx - alignment) & ~(alignment-1));
+      if (new_size_candidate <= aligned_max) {
+        desired_new_size = align_up(new_size_candidate, alignment);
       }
     }
   }
@@ -364,13 +366,14 @@ void DefNewGeneration::compute_new_size() {
   // All space sizes must be multiples of Generation::GenGrain.
   size_t alignment = Generation::GenGrain;
 
-  int threads_count = 0;
-  size_t thread_increase_size = 0;
+  int threads_count = Threads::number_of_non_daemon_threads();
+  size_t thread_increase_size = calculate_thread_increase_size(threads_count);
 
   size_t new_size_candidate = old_size / NewRatio;
   // Compute desired new generation size based on NewRatio and NewSizeThreadIncrease
   // and reverts to previous value if any overflow happens
-  size_t desired_new_size = adjust_for_thread_increase(new_size_candidate, new_size_before, alignment);
+  size_t desired_new_size = adjust_for_thread_increase(new_size_candidate, new_size_before,
+                                                       alignment, thread_increase_size);
 
   // Adjust new generation size
   desired_new_size = clamp(desired_new_size, min_new_size, max_new_size);

src/hotspot/share/gc/serial/defNewGeneration.hpp

@@ -341,7 +341,10 @@ class DefNewGeneration: public Generation {
   // If any overflow happens, revert to previous new size.
   size_t adjust_for_thread_increase(size_t new_size_candidate,
                                     size_t new_size_before,
-                                    size_t alignment) const;
+                                    size_t alignment,
+                                    size_t thread_increase_size) const;
+
+  size_t calculate_thread_increase_size(int threads_count) const;
 
 
   // Scavenge support

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

@@ -51,7 +51,8 @@ TenuredGeneration::TenuredGeneration(ReservedSpace rs,
   HeapWord* end    = (HeapWord*) _virtual_space.high();
   _the_space  = new TenuredSpace(_bts, MemRegion(bottom, end));
   _the_space->reset_saved_mark();
-  _shrink_factor = 0;
+  // If we don't shrink the heap in steps, '_shrink_factor' is always 100%.
+  _shrink_factor = ShrinkHeapInSteps ? 0 : 100;
   _capacity_at_prologue = 0;
 
   _gc_stats = new GCStats();

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

@@ -41,9 +41,11 @@ CardGeneration::CardGeneration(ReservedSpace rs,
                                size_t initial_byte_size,
                                CardTableRS* remset) :
   Generation(rs, initial_byte_size), _rs(remset),
-  _shrink_factor(0), _min_heap_delta_bytes(), _capacity_at_prologue(),
+  _min_heap_delta_bytes(), _capacity_at_prologue(),
   _used_at_prologue()
 {
+  // If we don't shrink the heap in steps, '_shrink_factor' is always 100%.
+  _shrink_factor = ShrinkHeapInSteps ? 0 : 100;
   HeapWord* start = (HeapWord*)rs.base();
   size_t reserved_byte_size = rs.size();
   assert((uintptr_t(start) & 3) == 0, "bad alignment");
@@ -186,7 +188,12 @@ void CardGeneration::invalidate_remembered_set() {
 void CardGeneration::compute_new_size() {
   assert(_shrink_factor <= 100, "invalid shrink factor");
   size_t current_shrink_factor = _shrink_factor;
-  _shrink_factor = 0;
+  if (ShrinkHeapInSteps) {
+    // Always reset '_shrink_factor' if the heap is shrunk in steps.
+    // If we shrink the heap in this iteration, '_shrink_factor' will
+    // be recomputed based on the old value further down in this fuction.
+    _shrink_factor = 0;
+  }
 
   // We don't have floating point command-line arguments
   // Note:  argument processing ensures that MinHeapFreeRatio < 100.