src/hotspot/share/gc/shenandoah/shenandoahMetrics.cpp

*** 41,14 ***
    _used_after = _heap->used();
    _if_after = _heap->free_set()->internal_fragmentation();
    _ef_after = _heap->free_set()->external_fragmentation();
  }
  
! bool ShenandoahMetricsSnapshot::is_good_progress() {
    // Under the critical threshold?
!   size_t free_actual   = _heap->free_set()->available();
!   size_t free_expected = _heap->max_capacity() / 100 * ShenandoahCriticalFreeThreshold;
    bool prog_free = free_actual >= free_expected;
    log_info(gc, ergo)("%s progress for free space: " SIZE_FORMAT "%s, need " SIZE_FORMAT "%s",
                       prog_free ? "Good" : "Bad",
                       byte_size_in_proper_unit(free_actual),   proper_unit_for_byte_size(free_actual),
                       byte_size_in_proper_unit(free_expected), proper_unit_for_byte_size(free_expected));
--- 41,32 ---
    _used_after = _heap->used();
    _if_after = _heap->free_set()->internal_fragmentation();
    _ef_after = _heap->free_set()->external_fragmentation();
  }
  
! // For degenerated GC, generation is Young in generational mode, Global in non-generational mode.
+ // For full GC, generation is always Global.
+ //
+ // Note that the size of the chosen collection set is proportional to the relevant generation's collection set.
+ // Note also that the generation size may change following selection of the collection set, as a side effect
+ // of evacuation.  Evacuation may promote objects, causing old to grow and young to shrink.  Or this may be a
+ // mixed evacuation.  When old regions are evacuated, this typically allows young to expand.  In all of these
+ // various scenarios, the purpose of asking is_good_progress() is to determine if there is enough memory available
+ // within young generation to justify making an attempt to perform a concurrent collection.  For this reason, we'll
+ // use the current size of the generation (which may not be different than when the collection set was chosen) to
+ // assess how much free memory we require in order to consider the most recent GC to have had good progress.
+ 
+ bool ShenandoahMetricsSnapshot::is_good_progress(ShenandoahGeneration* generation) {
    // Under the critical threshold?
!   ShenandoahFreeSet* free_set = _heap->free_set();
!   size_t free_actual   = free_set->available();
+ 
+   // ShenandoahCriticalFreeThreshold is expressed as a percentage.  We multiple this percentage by 1/100th
+   // of the generation capacity to determine whether the available memory within the generation exceeds the
+   // critical threshold.
+   size_t free_expected = (generation->max_capacity() / 100) * ShenandoahCriticalFreeThreshold;
+ 
    bool prog_free = free_actual >= free_expected;
    log_info(gc, ergo)("%s progress for free space: " SIZE_FORMAT "%s, need " SIZE_FORMAT "%s",
                       prog_free ? "Good" : "Bad",
                       byte_size_in_proper_unit(free_actual),   proper_unit_for_byte_size(free_actual),
                       byte_size_in_proper_unit(free_expected), proper_unit_for_byte_size(free_expected));