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8262185: G1: Prune collection set candidates early
Reviewed-by: iwalulya, sjohanss, ayang
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Thomas Schatzl committed Mar 1, 2021
1 parent 8bc8542 commit 702ca6228c7bcfaff6fa72e2f580daa7bb12f69a
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2019, 2020, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2019, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -35,6 +35,25 @@ void G1CollectionSetCandidates::remove(uint num_regions) {
}
}

void G1CollectionSetCandidates::remove_from_end(uint num_remove, size_t wasted) {
assert(num_remove <= num_remaining(), "trying to remove more regions than remaining");

#ifdef ASSERT
size_t reclaimable = 0;

for (uint i = 0; i < num_remove; i++) {
uint cur_idx = _num_regions - i - 1;
reclaimable += at(cur_idx)->reclaimable_bytes();
// Make sure we crash if we access it.
_regions[cur_idx] = NULL;
}

assert(reclaimable == wasted, "Recalculated reclaimable inconsistent");
#endif
_num_regions -= num_remove;
_remaining_reclaimable_bytes -= wasted;
}

void G1CollectionSetCandidates::iterate(HeapRegionClosure* cl) {
for (uint i = _front_idx; i < _num_regions; i++) {
HeapRegion* r = _regions[i];
@@ -45,6 +64,16 @@ void G1CollectionSetCandidates::iterate(HeapRegionClosure* cl) {
}
}

void G1CollectionSetCandidates::iterate_backwards(HeapRegionClosure* cl) {
for (uint i = _num_regions; i > _front_idx; i--) {
HeapRegion* r = _regions[i - 1];
if (cl->do_heap_region(r)) {
cl->set_incomplete();
break;
}
}
}

#ifndef PRODUCT
void G1CollectionSetCandidates::verify() const {
guarantee(_front_idx <= _num_regions, "Index: %u Num_regions: %u", _front_idx, _num_regions);
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2019, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -74,10 +74,16 @@ class G1CollectionSetCandidates : public CHeapObj<mtGC> {
return res;
}

// Remove num_regions from the front of the collection set candidate list.
void remove(uint num_regions);
// Remove num_remove regions from the back of the collection set candidate list.
void remove_from_end(uint num_remove, size_t wasted);

// Iterate over all remaining collection set candidate regions.
void iterate(HeapRegionClosure* cl);
// Iterate over all remaining collectin set candidate regions from the end
// to the beginning of the set.
void iterate_backwards(HeapRegionClosure* cl);

// Return the number of candidate regions remaining.
uint num_remaining() { return _num_regions - _front_idx; }
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2001, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -257,6 +257,60 @@ bool G1CollectionSetChooser::should_add(HeapRegion* hr) {
hr->rem_set()->is_complete();
}

// Closure implementing early pruning (removal) of regions meeting the
// G1HeapWastePercent criteria. That is, either until _max_pruned regions were
// removed (for forward progress in evacuation) or the waste accumulated by the
// removed regions is above max_wasted.
class G1PruneRegionClosure : public HeapRegionClosure {
uint _num_pruned;
size_t _cur_wasted;

uint const _max_pruned;
size_t const _max_wasted;

public:
G1PruneRegionClosure(uint max_pruned, size_t max_wasted) :
_num_pruned(0), _cur_wasted(0), _max_pruned(max_pruned), _max_wasted(max_wasted) { }

virtual bool do_heap_region(HeapRegion* r) {
size_t const reclaimable = r->reclaimable_bytes();
if (_num_pruned > _max_pruned ||
_cur_wasted + reclaimable > _max_wasted) {
return true;
}
r->rem_set()->clear(true /* cardset_only */);
_cur_wasted += reclaimable;
_num_pruned++;
return false;
}

uint num_pruned() const { return _num_pruned; }
size_t wasted() const { return _cur_wasted; }
};

void G1CollectionSetChooser::prune(G1CollectionSetCandidates* candidates) {
G1Policy* p = G1CollectedHeap::heap()->policy();

uint min_old_cset_length = p->calc_min_old_cset_length(candidates);
uint num_candidates = candidates->num_regions();

if (min_old_cset_length < num_candidates) {
size_t allowed_waste = p->allowed_waste_in_collection_set();

G1PruneRegionClosure prune_cl(num_candidates - min_old_cset_length,
allowed_waste);
candidates->iterate_backwards(&prune_cl);

log_debug(gc, ergo, cset)("Pruned %u regions out of %u, leaving " SIZE_FORMAT " bytes waste (allowed " SIZE_FORMAT ")",
prune_cl.num_pruned(),
candidates->num_regions(),
prune_cl.wasted(),
allowed_waste);

candidates->remove_from_end(prune_cl.num_pruned(), prune_cl.wasted());
}
}

G1CollectionSetCandidates* G1CollectionSetChooser::build(WorkGang* workers, uint max_num_regions) {
uint num_workers = workers->active_workers();
uint chunk_size = calculate_work_chunk_size(num_workers, max_num_regions);
@@ -265,6 +319,7 @@ G1CollectionSetCandidates* G1CollectionSetChooser::build(WorkGang* workers, uint
workers->run_task(&cl, num_workers);

G1CollectionSetCandidates* result = cl.get_sorted_candidates();
prune(result);
result->verify();
return result;
}
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2001, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -36,6 +36,11 @@ class WorkGang;
// methods.
class G1CollectionSetChooser : public AllStatic {
static uint calculate_work_chunk_size(uint num_workers, uint num_regions);

// Remove regions in the collection set candidates as long as the G1HeapWastePercent
// criteria is met. Keep at least the minimum amount of old regions to guarantee
// some progress.
static void prune(G1CollectionSetCandidates* candidates);
public:

static size_t mixed_gc_live_threshold_bytes() {
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2001, 2020, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2001, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -1278,22 +1278,16 @@ bool G1Policy::next_gc_should_be_mixed(const char* true_action_str,
log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str);
return false;
}

// Is the amount of uncollected reclaimable space above G1HeapWastePercent?
size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
double threshold = (double) G1HeapWastePercent;
if (reclaimable_percent <= threshold) {
log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
return false;
}
log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
// Go through all regions - we already pruned regions not worth collecting
// during candidate selection.
return true;
}

uint G1Policy::calc_min_old_cset_length() const {
size_t G1Policy::allowed_waste_in_collection_set() const {
return G1HeapWastePercent * _g1h->capacity() / 100;
}

uint G1Policy::calc_min_old_cset_length(G1CollectionSetCandidates* candidates) const {
// The min old CSet region bound is based on the maximum desired
// number of mixed GCs after a cycle. I.e., even if some old regions
// look expensive, we should add them to the CSet anyway to make
@@ -1304,7 +1298,7 @@ uint G1Policy::calc_min_old_cset_length() const {
// to the CSet candidates in the first place, not how many remain, so
// that the result is the same during all mixed GCs that follow a cycle.

const size_t region_num = _collection_set->candidates()->num_regions();
const size_t region_num = candidates->num_regions();
const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1);
size_t result = region_num / gc_num;
// emulate ceiling
@@ -1347,7 +1341,7 @@ void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* c

double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction();

const uint min_old_cset_length = calc_min_old_cset_length();
const uint min_old_cset_length = calc_min_old_cset_length(candidates);
const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length());
const uint max_optional_regions = max_old_cset_length - min_old_cset_length;
bool check_time_remaining = use_adaptive_young_list_length();
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2016, 2020, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2016, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -246,7 +246,7 @@ class G1Policy: public CHeapObj<mtGC> {

// Calculate the minimum number of old regions we'll add to the CSet
// during a mixed GC.
uint calc_min_old_cset_length() const;
uint calc_min_old_cset_length(G1CollectionSetCandidates* candidates) const;

// Calculate the maximum number of old regions we'll add to the CSet
// during a mixed GC.
@@ -347,6 +347,8 @@ class G1Policy: public CHeapObj<mtGC> {
bool next_gc_should_be_mixed(const char* true_action_str,
const char* false_action_str) const;

// Amount of allowed waste in bytes in the collection set.
size_t allowed_waste_in_collection_set() const;
// Calculate and return the number of initial and optional old gen regions from
// the given collection set candidates and the remaining time.
void calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates,

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