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src/hotspot/share/gc/g1/collectionSetChooser.cpp
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rev 53416 : imported patch 8217330-split-collectionsetchooser
rev 53417 : [mq]: 8217330-leo-review
@@ -1,7 +1,7 @@
/*
- * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2019, 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
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
@@ -26,21 +26,21 @@
#include "gc/g1/collectionSetChooser.hpp"
#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/heapRegionRemSet.hpp"
#include "gc/shared/space.inline.hpp"
#include "runtime/atomic.hpp"
+#include "utilities/quickSort.hpp"
-// Even though we don't use the GC efficiency in our heuristics as
-// much as we used to, we still order according to GC efficiency. This
-// will cause regions with a lot of live objects and large RSets to
-// end up at the end of the array. Given that we might skip collecting
-// the last few old regions, if after a few mixed GCs the remaining
-// have reclaimable bytes under a certain threshold, the hope is that
-// the ones we'll skip are ones with both large RSets and a lot of
-// live objects, not the ones with just a lot of live objects if we
+// Order regions according to GC efficiency. This will cause regions with a lot
+// of live objects and large remembered sets to end up at the end of the array.
+// Given that we might skip collecting the last few old regions, if after a few
+// mixed GCs the remaining have reclaimable bytes under a certain threshold, the
+// hope is that the ones we'll skip are ones with both large remembered sets and
+// a lot of live objects, not the ones with just a lot of live objects if we
// ordered according to the amount of reclaimable bytes per region.
static int order_regions(HeapRegion* hr1, HeapRegion* hr2) {
+ // Make sure that NULL entries are moved to the end.
if (hr1 == NULL) {
if (hr2 == NULL) {
return 0;
} else {
return 1;
@@ -49,197 +49,145 @@
return -1;
}
double gc_eff1 = hr1->gc_efficiency();
double gc_eff2 = hr2->gc_efficiency();
+
if (gc_eff1 > gc_eff2) {
return -1;
} if (gc_eff1 < gc_eff2) {
return 1;
} else {
return 0;
}
}
-static int order_regions(HeapRegion** hr1p, HeapRegion** hr2p) {
- return order_regions(*hr1p, *hr2p);
-}
+// Determine collection set candidates: For all regions determine whether they
+// should be a collection set candidates, calculate their efficiency, sort and
+// return them as G1CollectionSetCandidates instance.
+// Threads calculate the GC efficiency of the regions they get to process, and
+// put them into some work area unsorted. At the end the array is sorted and
+// copied into the G1CollectionSetCandidates instance; the caller will be the new
+// owner of this object.
+class G1BuildCandidateRegionsTask : public AbstractGangTask {
-CollectionSetChooser::CollectionSetChooser() :
- // The line below is the worst bit of C++ hackery I've ever written
- // (Detlefs, 11/23). You should think of it as equivalent to
- // "_regions(100, true)": initialize the growable array and inform it
- // that it should allocate its elem array(s) on the C heap.
- //
- // The first argument, however, is actually a comma expression
- // (set_allocation_type(this, C_HEAP), 100). The purpose of the
- // set_allocation_type() call is to replace the default allocation
- // type for embedded objects STACK_OR_EMBEDDED with C_HEAP. It will
- // allow to pass the assert in GenericGrowableArray() which checks
- // that a growable array object must be on C heap if elements are.
- //
- // Note: containing object is allocated on C heap since it is CHeapObj.
- //
- _regions((ResourceObj::set_allocation_type((address) &_regions,
- ResourceObj::C_HEAP),
- 100), true /* C_Heap */),
- _front(0), _end(0), _first_par_unreserved_idx(0),
- _region_live_threshold_bytes(0), _remaining_reclaimable_bytes(0) {
- _region_live_threshold_bytes = mixed_gc_live_threshold_bytes();
-}
+ // Work area for building the set of collection set candidates. Contains references
+ // to heap regions with their GC efficiencies calculated. To reduce contention
+ // on claiming array elements, worker threads claim parts of this array in chunks;
+ // Array elements may be NULL as threads might not get enough regions to fill
+ // up their chunks completely.
+ // Final sorting will remove them.
+ class G1BuildCandidateArray : public StackObj {
-#ifndef PRODUCT
-void CollectionSetChooser::verify() {
- guarantee(_end <= regions_length(), "_end: %u regions length: %u", _end, regions_length());
- guarantee(_front <= _end, "_front: %u _end: %u", _front, _end);
- uint index = 0;
- size_t sum_of_reclaimable_bytes = 0;
- while (index < _front) {
- guarantee(regions_at(index) == NULL,
- "all entries before _front should be NULL");
- index += 1;
- }
- HeapRegion *prev = NULL;
- while (index < _end) {
- HeapRegion *curr = regions_at(index++);
- guarantee(curr != NULL, "Regions in _regions array cannot be NULL");
- guarantee(!curr->is_young(), "should not be young!");
- guarantee(!curr->is_pinned(),
- "Pinned region should not be in collection set (index %u)", curr->hrm_index());
- if (prev != NULL) {
- guarantee(order_regions(prev, curr) != 1,
- "GC eff prev: %1.4f GC eff curr: %1.4f",
- prev->gc_efficiency(), curr->gc_efficiency());
- }
- sum_of_reclaimable_bytes += curr->reclaimable_bytes();
- prev = curr;
- }
- guarantee(sum_of_reclaimable_bytes == _remaining_reclaimable_bytes,
- "reclaimable bytes inconsistent, "
- "remaining: " SIZE_FORMAT " sum: " SIZE_FORMAT,
- _remaining_reclaimable_bytes, sum_of_reclaimable_bytes);
-}
-#endif // !PRODUCT
+ uint const _max_size;
+ uint const _chunk_size;
-void CollectionSetChooser::sort_regions() {
- // First trim any unused portion of the top in the parallel case.
- if (_first_par_unreserved_idx > 0) {
- assert(_first_par_unreserved_idx <= regions_length(),
- "Or we didn't reserved enough length");
- regions_trunc_to(_first_par_unreserved_idx);
- }
- _regions.sort(order_regions);
- assert(_end <= regions_length(), "Requirement");
-#ifdef ASSERT
- for (uint i = 0; i < _end; i++) {
- assert(regions_at(i) != NULL, "Should be true by sorting!");
- }
-#endif // ASSERT
- if (log_is_enabled(Trace, gc, liveness)) {
- G1PrintRegionLivenessInfoClosure cl("Post-Sorting");
- for (uint i = 0; i < _end; ++i) {
- HeapRegion* r = regions_at(i);
- cl.do_heap_region(r);
- }
- }
- verify();
-}
+ HeapRegion** _data;
-void CollectionSetChooser::add_region(HeapRegion* hr) {
- assert(!hr->is_pinned(),
- "Pinned region shouldn't be added to the collection set (index %u)", hr->hrm_index());
- assert(hr->is_old(), "should be old but is %s", hr->get_type_str());
- assert(hr->rem_set()->is_complete(),
- "Trying to add region %u to the collection set with incomplete remembered set", hr->hrm_index());
- _regions.append(hr);
- _end++;
- _remaining_reclaimable_bytes += hr->reclaimable_bytes();
- hr->calc_gc_efficiency();
-}
+ uint volatile _cur_claim_idx;
-void CollectionSetChooser::push(HeapRegion* hr) {
- assert(hr != NULL, "Can't put back a NULL region");
- assert(_front >= 1, "Too many regions have been put back");
- _front--;
- regions_at_put(_front, hr);
- _remaining_reclaimable_bytes += hr->reclaimable_bytes();
-}
+ // Calculates the maximum array size that will be used.
+ static uint required_array_size(uint num_regions, uint num_workers, uint chunk_size) {
+ uint const max_waste = num_workers * chunk_size;
+ // The array should be aligned with respect to chunk_size.
+ uint const aligned_num_regions = ((num_regions + chunk_size - 1) / chunk_size) * chunk_size;
-void CollectionSetChooser::prepare_for_par_region_addition(uint n_threads,
- uint n_regions,
- uint chunk_size) {
- _first_par_unreserved_idx = 0;
- uint max_waste = n_threads * chunk_size;
- // it should be aligned with respect to chunk_size
- uint aligned_n_regions = (n_regions + chunk_size - 1) / chunk_size * chunk_size;
- assert(aligned_n_regions % chunk_size == 0, "should be aligned");
- regions_at_put_grow(aligned_n_regions + max_waste - 1, NULL);
-}
+ return aligned_num_regions + max_waste;
+ }
-uint CollectionSetChooser::claim_array_chunk(uint chunk_size) {
- uint res = (uint) Atomic::add((jint) chunk_size,
- (volatile jint*) &_first_par_unreserved_idx);
- assert(regions_length() > res + chunk_size - 1,
- "Should already have been expanded");
- return res - chunk_size;
-}
+ public:
+ G1BuildCandidateArray(uint max_num_regions, uint num_workers, uint chunk_size) :
+ _max_size(required_array_size(max_num_regions, num_workers, chunk_size)),
+ _chunk_size(chunk_size),
+ _data(NEW_C_HEAP_ARRAY(HeapRegion*, _max_size, mtGC)),
+ _cur_claim_idx(0) {
+ for (uint i = 0; i < _max_size; i++) {
+ _data[i] = NULL;
+ }
+ }
-void CollectionSetChooser::set_region(uint index, HeapRegion* hr) {
- assert(regions_at(index) == NULL, "precondition");
- assert(hr->is_old(), "should be old but is %s", hr->get_type_str());
- regions_at_put(index, hr);
- hr->calc_gc_efficiency();
-}
+ ~G1BuildCandidateArray() {
+ FREE_C_HEAP_ARRAY(HeapRegion*, _data);
+ }
-void CollectionSetChooser::update_totals(uint region_num,
- size_t reclaimable_bytes) {
- // Only take the lock if we actually need to update the totals.
- if (region_num > 0) {
- assert(reclaimable_bytes > 0, "invariant");
- // We could have just used atomics instead of taking the
- // lock. However, we currently don't have an atomic add for size_t.
- MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
- _end += region_num;
- _remaining_reclaimable_bytes += reclaimable_bytes;
- } else {
- assert(reclaimable_bytes == 0, "invariant");
+ // Claim a new chunk, returning its bounds [from, to[.
+ void claim_chunk(uint& from, uint& to) {
+ uint result = Atomic::add(_chunk_size, &_cur_claim_idx);
+ assert(_max_size > result - 1,
+ "Array too small, is %u should be %u with chunk size %u.",
+ _max_size, result, _chunk_size);
+ from = result - _chunk_size;
+ to = result;
}
-}
-void CollectionSetChooser::iterate(HeapRegionClosure* cl) {
- for (uint i = _front; i < _end; i++) {
- HeapRegion* r = regions_at(i);
- if (cl->do_heap_region(r)) {
- cl->set_incomplete();
- break;
+ // Set element in array.
+ void set(uint idx, HeapRegion* hr) {
+ assert(idx < _max_size, "Index %u out of bounds %u", idx, _max_size);
+ assert(_data[idx] == NULL, "Value must not have been set.");
+ _data[idx] = hr;
}
+
+ void sort_and_copy_into(HeapRegion** dest, uint num_regions) {
+ if (_cur_claim_idx == 0) {
+ return;
}
-}
+ for (uint i = _cur_claim_idx; i < _max_size; i++) {
+ assert(_data[i] == NULL, "must be");
+ }
+ QuickSort::sort(_data, _cur_claim_idx, order_regions, true);
+ for (uint i = num_regions; i < _max_size; i++) {
+ assert(_data[i] == NULL, "must be");
+ }
+ for (uint i = 0; i < num_regions; i++) {
+ dest[i] = _data[i];
+ }
+ }
+ };
-void CollectionSetChooser::clear() {
- _regions.clear();
- _front = 0;
- _end = 0;
- _remaining_reclaimable_bytes = 0;
-}
+ // Per-region closure. In addition to determining whether a region should be
+ // added to the candidates, and calculating those regions' gc efficiencies, also
+ // gather additional statistics.
+ class G1BuildCandidateRegionsClosure : public HeapRegionClosure {
+ G1BuildCandidateArray* _array;
-class ParKnownGarbageHRClosure: public HeapRegionClosure {
- G1CollectedHeap* _g1h;
- CSetChooserParUpdater _cset_updater;
+ uint _cur_chunk_idx;
+ uint _cur_chunk_end;
-public:
- ParKnownGarbageHRClosure(CollectionSetChooser* hrSorted,
- uint chunk_size) :
- _g1h(G1CollectedHeap::heap()),
- _cset_updater(hrSorted, true /* parallel */, chunk_size) { }
+ uint _regions_added;
+ size_t _reclaimable_bytes_added;
+
+ void add_region(HeapRegion* hr) {
+ if (_cur_chunk_idx == _cur_chunk_end) {
+ _array->claim_chunk(_cur_chunk_idx, _cur_chunk_end);
+ }
+ assert(_cur_chunk_idx < _cur_chunk_end, "Must be");
+
+ hr->calc_gc_efficiency();
+ _array->set(_cur_chunk_idx, hr);
+
+ _cur_chunk_idx++;
+
+ _regions_added++;
+ _reclaimable_bytes_added += hr->reclaimable_bytes();
+ }
+
+ bool should_add(HeapRegion* hr) { return CollectionSetChooser::should_add(hr); }
+
+ public:
+ G1BuildCandidateRegionsClosure(G1BuildCandidateArray* array) :
+ _array(array),
+ _cur_chunk_idx(0),
+ _cur_chunk_end(0),
+ _regions_added(0),
+ _reclaimable_bytes_added(0) { }
bool do_heap_region(HeapRegion* r) {
// We will skip any region that's currently used as an old GC
// alloc region (we should not consider those for collection
// before we fill them up).
- if (_cset_updater.should_add(r) && !_g1h->is_old_gc_alloc_region(r)) {
- _cset_updater.add_region(r);
+ if (should_add(r) && !G1CollectedHeap::heap()->is_old_gc_alloc_region(r)) {
+ add_region(r);
} else if (r->is_old()) {
// Keep remembered sets for humongous regions, otherwise clean out remembered
// sets for old regions.
r->rem_set()->clear(true /* only_cardset */);
} else {
@@ -247,56 +195,75 @@
"Missed to clear unused remembered set of region %u (%s) that is %s",
r->hrm_index(), r->get_type_str(), r->rem_set()->get_state_str());
}
return false;
}
-};
-class ParKnownGarbageTask: public AbstractGangTask {
- CollectionSetChooser* _hrSorted;
- uint _chunk_size;
+ uint regions_added() const { return _regions_added; }
+ size_t reclaimable_bytes_added() const { return _reclaimable_bytes_added; }
+ };
+
G1CollectedHeap* _g1h;
HeapRegionClaimer _hrclaimer;
+ uint volatile _num_regions_added;
+ size_t volatile _reclaimable_bytes_added;
+
+ G1BuildCandidateArray _result;
+
+ void update_totals(uint num_regions, size_t reclaimable_bytes) {
+ if (num_regions > 0) {
+ assert(reclaimable_bytes > 0, "invariant");
+ Atomic::add(num_regions, &_num_regions_added);
+ Atomic::add(reclaimable_bytes, &_reclaimable_bytes_added);
+ } else {
+ assert(reclaimable_bytes == 0, "invariant");
+ }
+ }
+
public:
- ParKnownGarbageTask(CollectionSetChooser* hrSorted, uint chunk_size, uint n_workers) :
- AbstractGangTask("ParKnownGarbageTask"),
- _hrSorted(hrSorted), _chunk_size(chunk_size),
- _g1h(G1CollectedHeap::heap()), _hrclaimer(n_workers) {}
+ G1BuildCandidateRegionsTask(uint max_num_regions, uint chunk_size, uint num_workers) :
+ AbstractGangTask("G1 Build Candidate Regions"),
+ _g1h(G1CollectedHeap::heap()),
+ _hrclaimer(num_workers),
+ _num_regions_added(0),
+ _reclaimable_bytes_added(0),
+ _result(max_num_regions, chunk_size, num_workers) { }
void work(uint worker_id) {
- ParKnownGarbageHRClosure par_known_garbage_cl(_hrSorted, _chunk_size);
- _g1h->heap_region_par_iterate_from_worker_offset(&par_known_garbage_cl, &_hrclaimer, worker_id);
+ G1BuildCandidateRegionsClosure cl(&_result);
+ _g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hrclaimer, worker_id);
+ update_totals(cl.regions_added(), cl.reclaimable_bytes_added());
}
-};
-uint CollectionSetChooser::calculate_parallel_work_chunk_size(uint n_workers, uint n_regions) const {
- assert(n_workers > 0, "Active gc workers should be greater than 0");
- const uint overpartition_factor = 4;
- const uint min_chunk_size = MAX2(n_regions / n_workers, 1U);
- return MAX2(n_regions / (n_workers * overpartition_factor), min_chunk_size);
-}
+ G1CollectionSetCandidates* get_sorted_candidates() {
+ HeapRegion** regions = NEW_C_HEAP_ARRAY(HeapRegion*, _num_regions_added, mtGC);
+ _result.sort_and_copy_into(regions, _num_regions_added);
+ return new G1CollectionSetCandidates(regions,
+ _num_regions_added,
+ _reclaimable_bytes_added);
+ }
+};
-bool CollectionSetChooser::region_occupancy_low_enough_for_evac(size_t live_bytes) {
- return live_bytes < mixed_gc_live_threshold_bytes();
+uint CollectionSetChooser::calculate_work_chunk_size(uint num_workers, uint num_regions) {
+ assert(num_workers > 0, "Active gc workers should be greater than 0");
+ return MAX2(num_regions / num_workers, 1U);
}
-bool CollectionSetChooser::should_add(HeapRegion* hr) const {
+bool CollectionSetChooser::should_add(HeapRegion* hr) {
return !hr->is_young() &&
!hr->is_pinned() &&
region_occupancy_low_enough_for_evac(hr->live_bytes()) &&
hr->rem_set()->is_complete();
}
-void CollectionSetChooser::rebuild(WorkGang* workers, uint n_regions) {
- clear();
-
- uint n_workers = workers->active_workers();
-
- uint chunk_size = calculate_parallel_work_chunk_size(n_workers, n_regions);
- prepare_for_par_region_addition(n_workers, n_regions, chunk_size);
-
- ParKnownGarbageTask par_known_garbage_task(this, chunk_size, n_workers);
- workers->run_task(&par_known_garbage_task);
-
- sort_regions();
+G1CollectionSetCandidates* CollectionSetChooser::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);
+
+ G1BuildCandidateRegionsTask cl(max_num_regions, chunk_size, num_workers);
+ workers->run_task(&cl, num_workers);
+
+ G1CollectionSetCandidates* result = cl.get_sorted_candidates();
+ result->verify();
+ return result;
}
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