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8302215: G1: Last-ditch Full GC should do serial compaction for tail regions in per thread compaction points.

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Reviewed-by: ayang, sjohanss, tschatzl
This commit is contained in:
Ivan Walulya 2023-02-20 08:43:02 +00:00
parent 7e08275cc1
commit eaae0baeba
8 changed files with 88 additions and 40 deletions
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76
src/hotspot/share/gc/g1/g1FullCollector.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2017, 2023, 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
@ -327,7 +327,7 @@ void G1FullCollector::phase2_prepare_compaction() {
// Try to avoid OOM immediately after Full GC in case there are no free regions
// left after determining the result locations (i.e. this phase). Prepare to
// maximally compact the tail regions of the compaction queues serially.
if (!has_free_compaction_targets) {
if (scope()->do_maximal_compaction() || !has_free_compaction_targets) {
phase2c_prepare_serial_compaction();
}
}
@ -348,37 +348,67 @@ bool G1FullCollector::phase2b_forward_oops() {
return task.has_free_compaction_targets();
}
void G1FullCollector::phase2c_prepare_serial_compaction() {
GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare serial compaction", scope()->timer());
// At this point we know that after parallel compaction there will be no
// completely free regions. That means that the last region of
// all compaction queues still have data in them. We try to compact
// these regions in serial to avoid a premature OOM when the mutator wants
// to allocate the first eden region after gc.
uint G1FullCollector::truncate_parallel_cps() {
uint lowest_current = (uint)-1;
for (uint i = 0; i < workers(); i++) {
G1FullGCCompactionPoint* cp = compaction_point(i);
if (cp->has_regions()) {
serial_compaction_point()->add(cp->remove_last());
lowest_current = MIN2(lowest_current, cp->current_region()->hrm_index());
}
}
// Update the forwarding information for the regions in the serial
// compaction point.
G1FullGCCompactionPoint* cp = serial_compaction_point();
for (GrowableArrayIterator<HeapRegion*> it = cp->regions()->begin(); it != cp->regions()->end(); ++it) {
HeapRegion* current = *it;
if (!cp->is_initialized()) {
// Initialize the compaction point. Nothing more is needed for the first heap region
// since it is already prepared for compaction.
cp->initialize(current);
} else {
assert(!current->is_humongous(), "Should be no humongous regions in compaction queue");
G1SerialRePrepareClosure re_prepare(cp, current);
if (lowest_current == (uint)-1) {
// worker compaction points are empty
return lowest_current;
}
for (uint i = 0; i < workers(); i++) {
G1FullGCCompactionPoint* cp = compaction_point(i);
if (cp->has_regions()) {
cp->remove_at_or_above(lowest_current);
}
}
return lowest_current;
}
void G1FullCollector::phase2c_prepare_serial_compaction() {
GCTraceTime(Debug, gc, phases) debug("Phase 2: Prepare serial compaction", scope()->timer());
// At this point, we know that after parallel compaction there will be regions that
// are partially compacted into. Thus, the last compaction region of all
// compaction queues still have space in them. We try to re-compact these regions
// in serial to avoid a premature OOM when the mutator wants to allocate the first
// eden region after gc.
// For maximum compaction, we need to re-prepare all objects above the lowest
// region among the current regions for all thread compaction points. It may
// happen that due to the uneven distribution of objects to parallel threads, holes
// have been created as threads compact to different target regions between the
// lowest and the highest region in the tails of the compaction points.
uint start_serial = truncate_parallel_cps();
if (start_serial >= _heap->max_reserved_regions()) {
return;
}
G1FullGCCompactionPoint* serial_cp = serial_compaction_point();
assert(!serial_cp->is_initialized(), "sanity!");
HeapRegion* start_hr = _heap->region_at(start_serial);
serial_cp->add(start_hr);
serial_cp->initialize(start_hr);
HeapWord* dense_prefix_top = compaction_top(start_hr);
G1SerialRePrepareClosure re_prepare(serial_cp, dense_prefix_top);
for (uint i = start_serial + 1; i < _heap->max_reserved_regions(); i++) {
if (is_compaction_target(i)) {
HeapRegion* current = _heap->region_at(i);
set_compaction_top(current, current->bottom());
serial_cp->add(current);
current->apply_to_marked_objects(mark_bitmap(), &re_prepare);
}
}
cp->update();
serial_cp->update();
}
void G1FullCollector::phase3_adjust_pointers() {

4
src/hotspot/share/gc/g1/g1FullCollector.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2017, 2023, 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
@ -137,6 +137,8 @@ public:
inline void set_compaction_top(HeapRegion* r, HeapWord* value);
inline HeapWord* compaction_top(HeapRegion* r) const;
uint truncate_parallel_cps();
private:
void phase1_mark_live_objects();
void phase2_prepare_compaction();

17
src/hotspot/share/gc/g1/g1FullGCCompactionPoint.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2017, 2023, 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
@ -116,6 +116,17 @@ void G1FullGCCompactionPoint::add(HeapRegion* hr) {
_compaction_regions->append(hr);
}
HeapRegion* G1FullGCCompactionPoint::remove_last() {
return _compaction_regions->pop();
void G1FullGCCompactionPoint::remove_at_or_above(uint bottom) {
HeapRegion* cur = current_region();
assert(cur->hrm_index() >= bottom, "Sanity!");
int start_index = 0;
for (HeapRegion* r : *_compaction_regions) {
if (r->hrm_index() < bottom) {
start_index++;
}
}
assert(start_index >= 0, "Should have at least one region");
_compaction_regions->trunc_to(start_index);
}

4
src/hotspot/share/gc/g1/g1FullGCCompactionPoint.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2017, 2023, 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
@ -55,7 +55,7 @@ public:
void forward(oop object, size_t size);
void add(HeapRegion* hr);
HeapRegion* remove_last();
void remove_at_or_above(uint bottom);
HeapRegion* current_region();
GrowableArray<HeapRegion*>* regions();

8
src/hotspot/share/gc/g1/g1FullGCPrepareTask.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2017, 2023, 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
@ -119,12 +119,12 @@ private:
// serial compaction.
class G1SerialRePrepareClosure : public StackObj {
G1FullGCCompactionPoint* _cp;
HeapRegion* _current;
HeapWord* _dense_prefix_top;
public:
G1SerialRePrepareClosure(G1FullGCCompactionPoint* hrcp, HeapRegion* hr) :
G1SerialRePrepareClosure(G1FullGCCompactionPoint* hrcp, HeapWord* dense_prefix_top) :
_cp(hrcp),
_current(hr) { }
_dense_prefix_top(dense_prefix_top) { }
inline size_t apply(oop obj);
};

12
src/hotspot/share/gc/g1/g1FullGCPrepareTask.inline.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2022, 2023, 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
@ -110,10 +110,12 @@ inline bool G1DetermineCompactionQueueClosure::do_heap_region(HeapRegion* hr) {
}
inline size_t G1SerialRePrepareClosure::apply(oop obj) {
// We only re-prepare objects forwarded within the current region, so
// skip objects that are already forwarded to another region.
if (obj->is_forwarded() && !_current->is_in(obj->forwardee())) {
return obj->size();
if (obj->is_forwarded()) {
// We skip objects compiled into the first region or
// into regions not part of the serial compaction point.
if (cast_from_oop<HeapWord*>(obj->forwardee()) < _dense_prefix_top) {
return obj->size();
}
}
// Get size and forward.

3
src/hotspot/share/gc/g1/g1FullGCScope.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2017, 2023, 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
@ -43,6 +43,7 @@ G1FullGCScope::G1FullGCScope(G1MonitoringSupport* monitoring_support,
G1FullGCTracer* tracer) :
_rm(),
_explicit_gc(explicit_gc),
_do_maximal_compaction(do_maximal_compaction),
_g1h(G1CollectedHeap::heap()),
_svc_marker(SvcGCMarker::FULL),
_timer(),

4
src/hotspot/share/gc/g1/g1FullGCScope.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2017, 2023, 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
@ -48,6 +48,7 @@ public:
class G1FullGCScope : public StackObj {
ResourceMark _rm;
bool _explicit_gc;
bool _do_maximal_compaction;
G1CollectedHeap* _g1h;
SvcGCMarker _svc_marker;
STWGCTimer _timer;
@ -68,6 +69,7 @@ public:
bool is_explicit_gc();
bool should_clear_soft_refs();
bool do_maximal_compaction() { return _do_maximal_compaction; }
STWGCTimer* timer();
G1FullGCTracer* tracer();