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Reduce number of gen 2 GC under high memory load #83328

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Reduce number of gen 2 GC under high memory load #83328

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74edf60
Port the logic from .NET Framework.
PeterSolMS Mar 9, 2023
8eaf102
Merge branch 'main' into Reduce_number_of_GC_under_high_memory_load
PeterSolMS Jul 13, 2023
052edc3
Introduce a flag high_memory_compact_gtc_p to inform decide_on_compac…
PeterSolMS Jul 13, 2023
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59 changes: 54 additions & 5 deletions src/coreclr/gc/gc.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2374,6 +2374,8 @@ gc_latency_level gc_heap::latency_level = latency_level_default;

gc_mechanisms gc_heap::settings;

BOOL gc_heap::high_memory_compact_gtc_p;

gc_history_global gc_heap::gc_data_global;

uint64_t gc_heap::gc_last_ephemeral_decommit_time = 0;
Expand Down Expand Up @@ -2924,6 +2926,7 @@ BOOL gc_heap::heap_analyze_enabled = FALSE;

#ifndef MULTIPLE_HEAPS

bool gc_heap::maxgen_size_inc_per_heap_p = false;
alloc_list gc_heap::loh_alloc_list [NUM_LOH_ALIST-1];
alloc_list gc_heap::gen2_alloc_list[NUM_GEN2_ALIST-1];
alloc_list gc_heap::poh_alloc_list [NUM_POH_ALIST-1];
Expand Down Expand Up @@ -14754,6 +14757,8 @@ gc_heap::init_gc_heap (int h_number)

gen0_allocated_after_gc_p = false;

maxgen_size_inc_per_heap_p = false;

#ifdef RECORD_LOH_STATE
loh_state_index = 0;
#endif //RECORD_LOH_STATE
Expand Down Expand Up @@ -21442,19 +21447,29 @@ int gc_heap::generation_to_condemn (int n_initial,

high_memory_load = TRUE;

BOOL check_fragmentation = TRUE;
if (conserve_mem_setting != 0)
{
// optimization for high memory situations: check fragmentation only if
// we are about to do a gen 2 collection anyway or gen 2 grew in the last gen 1.
dynamic_data* dd_max = dynamic_data_of (max_generation);
bool would_trigger_gen2_p = (n == max_generation) || (((float)dd_new_allocation (dd_max) / (float)dd_desired_allocation (dd_max)) < 0.9);
check_fragmentation = (would_trigger_gen2_p || maxgen_size_inc_per_heap_p);
}

if (memory_load >= v_high_memory_load_th || low_memory_detected)
{
// TODO: Perhaps in 64-bit we should be estimating gen1's fragmentation as well since
// gen1/gen0 may take a lot more memory than gen2.
if (!high_fragmentation)
if (!high_fragmentation && check_fragmentation)
{
high_fragmentation = dt_estimate_reclaim_space_p (tuning_deciding_condemned_gen, max_generation);
}
v_high_memory_load = TRUE;
}
else
{
if (!high_fragmentation)
if (!high_fragmentation && check_fragmentation)
{
high_fragmentation = dt_estimate_high_frag_p (tuning_deciding_condemned_gen, max_generation, available_physical);
}
Expand Down Expand Up @@ -23732,6 +23747,10 @@ void gc_heap::garbage_collect (int n)
STRESS_HEAP_ARG(n)
);

// we have decided to do a blocking gen 2 collection due to high memory
// set flag so that decide_on_compacting can do the right thing
high_memory_compact_gtc_p = (settings.condemned_generation == max_generation) && should_do_blocking_collection;

STRESS_LOG1(LF_GCROOTS|LF_GC|LF_GCALLOC, LL_INFO10,
"condemned generation num: %d\n", settings.condemned_generation);

Expand Down Expand Up @@ -28739,6 +28758,9 @@ void gc_heap::mark_phase (int condemned_gen_number, BOOL mark_only_p)
static BOOL do_mark_steal_p = FALSE;
#endif //MH_SC_MARK

if (condemned_gen_number >= (max_generation - 1))
maxgen_size_inc_per_heap_p = false;

#ifdef FEATURE_CARD_MARKING_STEALING
reset_card_marking_enumerators();
#endif // FEATURE_CARD_MARKING_STEALING
Expand Down Expand Up @@ -32691,7 +32713,7 @@ void gc_heap::plan_phase (int condemned_gen_number)
dprintf (1, ("gen2 grew %zd (end seg alloc: %zd, condemned alloc: %zd",
growth, end_seg_allocated, condemned_allocated));

maxgen_size_inc_p = true;
maxgen_size_inc_per_heap_p = true;
}
else
{
Expand Down Expand Up @@ -32841,6 +32863,19 @@ void gc_heap::plan_phase (int condemned_gen_number)
}
}
#endif //!USE_REGIONS
// count number of heaps seeing gen 2 growth
int maxgen_size_inc_count = 0;
for (int i = 0; i < n_heaps; i++)
{
if (g_heaps[i]->maxgen_size_inc_per_heap_p)
{
maxgen_size_inc_count += 1;
}
}
// if it's the majority, set the global flag
if (maxgen_size_inc_count > (n_heaps / 2))
maxgen_size_inc_p = true;

if (maxgen_size_inc_p && provisional_mode_triggered
#ifdef BACKGROUND_GC
&& !is_bgc_in_progress()
Expand Down Expand Up @@ -32982,6 +33017,9 @@ void gc_heap::plan_phase (int condemned_gen_number)
rearrange_uoh_segments ();
}
#endif //!USE_REGIONS

maxgen_size_inc_p = maxgen_size_inc_per_heap_p;

if (maxgen_size_inc_p && provisional_mode_triggered
#ifdef BACKGROUND_GC
&& !is_bgc_in_progress()
Expand Down Expand Up @@ -44107,6 +44145,13 @@ BOOL gc_heap::decide_on_compacting (int condemned_gen_number,
#endif // BACKGROUND_GC
}

// if generation_to_condemn decided to do a full blocking GC,
// make sure to compact
if (high_memory_compact_gtc_p)
{
should_compact = TRUE;
}

#ifdef HOST_64BIT
// check for high memory situation
if(!should_compact)
Expand All @@ -44116,8 +44161,7 @@ BOOL gc_heap::decide_on_compacting (int condemned_gen_number,
num_heaps = gc_heap::n_heaps;
#endif // MULTIPLE_HEAPS

ptrdiff_t reclaim_space = generation_size(max_generation) - generation_plan_size(max_generation);

ptrdiff_t reclaim_space = fragmentation;
if((settings.entry_memory_load >= high_memory_load_th) && (settings.entry_memory_load < v_high_memory_load_th))
{
if(reclaim_space > (int64_t)(min_high_fragmentation_threshold (entry_available_physical_mem, num_heaps)))
Expand Down Expand Up @@ -45663,6 +45707,11 @@ void gc_heap::background_sweep()
current_sweep_seg = 0;
#endif //DOUBLY_LINKED_FL

// we just finished sweeping and thus created more space in gen 2
// so turn off this flag which may have been turned on by a gen 1
// collection that occurred before or during this background GC
maxgen_size_inc_per_heap_p = false;

enable_preemptive ();

#ifdef MULTIPLE_HEAPS
Expand Down
4 changes: 4 additions & 0 deletions src/coreclr/gc/gcpriv.h
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Expand Up @@ -3430,6 +3430,8 @@ class gc_heap
PER_HEAP_FIELD_SINGLE_GC bool no_gc_oom_p;
PER_HEAP_FIELD_SINGLE_GC heap_segment* saved_loh_segment_no_gc;

PER_HEAP_FIELD_SINGLE_GC bool maxgen_size_inc_per_heap_p;

#ifdef MULTIPLE_HEAPS
#ifdef USE_REGIONS
PER_HEAP_FIELD_SINGLE_GC min_fl_list_info* min_fl_list;
Expand Down Expand Up @@ -4057,6 +4059,8 @@ class gc_heap

PER_HEAP_ISOLATED_FIELD_SINGLE_GC gc_mechanisms settings;

PER_HEAP_ISOLATED_FIELD_SINGLE_GC BOOL high_memory_compact_gtc_p;

#ifdef MULTIPLE_HEAPS
// These 2 fields' values do not change but are set/unset per GC
PER_HEAP_ISOLATED_FIELD_SINGLE_GC GCEvent gc_start_event;
Expand Down