--- old/src/hotspot/share/gc/g1/g1HeapSizingPolicy.cpp	2020-02-17 17:22:56.740263166 +0800
+++ new/src/hotspot/share/gc/g1/g1HeapSizingPolicy.cpp	2020-02-17 17:22:56.743263274 +0800
@@ -26,6 +26,7 @@
 #include "gc/g1/g1CollectedHeap.hpp"
 #include "gc/g1/g1HeapSizingPolicy.hpp"
 #include "gc/g1/g1Analytics.hpp"
+#include "gc/g1/g1Policy.hpp"
 #include "logging/log.hpp"
 #include "runtime/globals.hpp"
 #include "utilities/debug.hpp"
@@ -38,7 +39,8 @@
 G1HeapSizingPolicy::G1HeapSizingPolicy(const G1CollectedHeap* g1h, const G1Analytics* analytics) :
   _g1h(g1h),
   _analytics(analytics),
-  _num_prev_pauses_for_heuristics(analytics->number_of_recorded_pause_times()) {
+  _num_prev_pauses_for_heuristics(analytics->number_of_recorded_pause_times()),
+  _minimum_desired_bytes_after_last_cm(MinHeapSize) {
 
   assert(MinOverThresholdForGrowth < _num_prev_pauses_for_heuristics, "Threshold must be less than %u", _num_prev_pauses_for_heuristics);
   clear_ratio_check_data();
@@ -50,7 +52,7 @@
   _pauses_since_start = 0;
 }
 
-size_t G1HeapSizingPolicy::expansion_amount() {
+size_t G1HeapSizingPolicy::expansion_amount_after_young_collection() {
   double recent_gc_overhead = _analytics->recent_avg_pause_time_ratio() * 100.0;
   double last_gc_overhead = _analytics->last_pause_time_ratio() * 100.0;
   assert(GCTimeRatio > 0,
@@ -160,3 +162,52 @@
 
   return expand_bytes;
 }
+
+size_t G1HeapSizingPolicy::target_heap_capacity(size_t used_bytes,  uintx free_ratio) {
+  const double free_percentage = (double) free_ratio / 100.0;
+  const double used_percentage = 1.0 - free_percentage;
+
+  // We have to be careful here as these two calculations can overflow
+  // 32-bit size_t's.
+  double used_bytes_d = (double) used_bytes;
+  double desired_capacity_d = used_bytes_d / used_percentage;
+  // Let's make sure that they are both under the max heap size, which
+  // by default will make it fit into a size_t.
+  double desired_capacity_upper_bound = (double) MaxHeapSize;
+  desired_capacity_d = MIN2(desired_capacity_d, desired_capacity_upper_bound);
+  // We can now safely turn it into size_t's.
+  return (size_t) desired_capacity_d;
+}
+
+size_t G1HeapSizingPolicy::expansion_amount_after_concurrent_mark() {
+  size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
+
+  size_t minimum_desired_capacity = target_heap_capacity(cur_used_bytes, MinHeapFreeRatio);
+
+  _minimum_desired_bytes_after_last_cm = _g1h->policy()->minimum_desired_bytes_after_concurrent_mark(cur_used_bytes);
+  // Use the smaller one between minimum_desired_capacity
+  // and predicted minimum_desired_bytes_after_concurrent_mark
+  // We still use minimum_desired_capacity because minimum_desired_bytes_after_concurrent_mark
+  // might include a lot of new allocated humongous objects
+  _minimum_desired_bytes_after_last_cm = MIN2(_minimum_desired_bytes_after_last_cm, minimum_desired_capacity);
+
+  return _minimum_desired_bytes_after_last_cm > _g1h->capacity() ?
+         _minimum_desired_bytes_after_last_cm - _g1h->capacity() : 0;
+}
+
+size_t G1HeapSizingPolicy::shrink_amount_after_mixed_collections() {
+  size_t shrink_bytes = 0;
+  const size_t capacity_after_gc = _g1h->capacity();
+  const size_t used_after_gc = capacity_after_gc - _g1h->unused_committed_regions_in_bytes();
+  size_t maximum_desired_capacity = target_heap_capacity(used_after_gc, MaxHeapFreeRatio);
+  // soft_max_capacity can be smaller
+  maximum_desired_capacity = MIN2(maximum_desired_capacity, _g1h->soft_max_capacity());
+  // Make sure not less than _minimum_desired_bytes_after_last_cm
+  maximum_desired_capacity = MAX2(maximum_desired_capacity, _minimum_desired_bytes_after_last_cm);
+
+  if (capacity_after_gc > maximum_desired_capacity) {
+    shrink_bytes = capacity_after_gc - maximum_desired_capacity;
+  }
+
+  return shrink_bytes;
+}