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8253169: [BACKOUT] Improve large object handling during evacuation
Revert "8027545: Improve object array chunking test in G1's copy_to_survivor_space"
Revert "8158045: Improve large object handling during evacuation"
Revert "8027761: Investigate fast-path for scanning only objects with references during gc"

Reviewed-by: tschatzl, sjohanss
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Kim Barrett committed Sep 15, 2020
1 parent b5620a3 commit 74851c507bed9eb2e1e0b0eac3b53a74decb2588
@@ -31,19 +31,15 @@
#include "gc/g1/g1RootClosures.hpp"
#include "gc/g1/g1StringDedup.hpp"
#include "gc/g1/g1Trace.hpp"
#include "gc/shared/partialArrayTaskStepper.inline.hpp"
#include "gc/shared/taskqueue.inline.hpp"
#include "memory/allocation.inline.hpp"
#include "oops/access.inline.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/prefetch.inline.hpp"
#include "utilities/globalDefinitions.hpp"

G1ParScanThreadState::G1ParScanThreadState(G1CollectedHeap* g1h,
G1RedirtyCardsQueueSet* rdcqs,
uint worker_id,
uint n_workers,
size_t young_cset_length,
size_t optional_cset_length)
: _g1h(g1h),
@@ -64,8 +60,6 @@ G1ParScanThreadState::G1ParScanThreadState(G1CollectedHeap* g1h,
_surviving_young_words(NULL),
_surviving_words_length(young_cset_length + 1),
_old_gen_is_full(false),
_partial_objarray_chunk_size(ParGCArrayScanChunk),
_partial_array_stepper(n_workers),
_num_optional_regions(optional_cset_length),
_numa(g1h->numa()),
_obj_alloc_stat(NULL)
@@ -205,59 +199,48 @@ void G1ParScanThreadState::do_partial_array(PartialArrayScanTask task) {

assert(_g1h->is_in_reserved(from_obj), "must be in heap.");
assert(from_obj->is_objArray(), "must be obj array");
assert(from_obj->is_forwarded(), "must be forwarded");
objArrayOop from_obj_array = objArrayOop(from_obj);
// The from-space object contains the real length.
int length = from_obj_array->length();

oop to_obj = from_obj->forwardee();
assert(from_obj->is_forwarded(), "must be forwarded");
oop to_obj = from_obj->forwardee();
assert(from_obj != to_obj, "should not be chunking self-forwarded objects");
assert(to_obj->is_objArray(), "must be obj array");
objArrayOop to_array = objArrayOop(to_obj);

PartialArrayTaskStepper::Step step
= _partial_array_stepper.next(objArrayOop(from_obj),
to_array,
_partial_objarray_chunk_size);
for (uint i = 0; i < step._ncreate; ++i) {
objArrayOop to_obj_array = objArrayOop(to_obj);
// We keep track of the next start index in the length field of the
// to-space object.
int next_index = to_obj_array->length();
assert(0 <= next_index && next_index < length,
"invariant, next index: %d, length: %d", next_index, length);

int start = next_index;
int end = length;
int remainder = end - start;
// We'll try not to push a range that's smaller than ParGCArrayScanChunk.
if (remainder > 2 * ParGCArrayScanChunk) {
end = start + ParGCArrayScanChunk;
to_obj_array->set_length(end);
// Push the remainder before we process the range in case another
// worker has run out of things to do and can steal it.
push_on_queue(ScannerTask(PartialArrayScanTask(from_obj)));
} else {
assert(length == end, "sanity");
// We'll process the final range for this object. Restore the length
// so that the heap remains parsable in case of evacuation failure.
to_obj_array->set_length(end);
}

HeapRegion* hr = _g1h->heap_region_containing(to_array);
HeapRegion* hr = _g1h->heap_region_containing(to_obj);
G1ScanInYoungSetter x(&_scanner, hr->is_young());
// Process claimed task. The length of to_array is not correct, but
// fortunately the iteration ignores the length field and just relies
// on start/end.
to_array->oop_iterate_range(&_scanner,
step._index,
step._index + _partial_objarray_chunk_size);
}

void G1ParScanThreadState::start_partial_objarray(G1HeapRegionAttr dest_attr,
oop from_obj,
oop to_obj) {
assert(from_obj->is_objArray(), "precondition");
assert(from_obj->is_forwarded(), "precondition");
assert(from_obj->forwardee() == to_obj, "precondition");
assert(from_obj != to_obj, "should not be scanning self-forwarded objects");
assert(to_obj->is_objArray(), "precondition");

objArrayOop to_array = objArrayOop(to_obj);

PartialArrayTaskStepper::Step step
= _partial_array_stepper.start(objArrayOop(from_obj),
to_array,
_partial_objarray_chunk_size);

// Push any needed partial scan tasks. Pushed before processing the
// intitial chunk to allow other workers to steal while we're processing.
for (uint i = 0; i < step._ncreate; ++i) {
push_on_queue(ScannerTask(PartialArrayScanTask(from_obj)));
}

G1ScanInYoungSetter x(&_scanner, dest_attr.is_young());
// Process the initial chunk. No need to process the type in the
// klass, as it will already be handled by processing the built-in
// module. The length of to_array is not correct, but fortunately
// the iteration ignores that length field and relies on start/end.
to_array->oop_iterate_range(&_scanner, 0, step._index);
// Process indexes [start,end). It will also process the header
// along with the first chunk (i.e., the chunk with start == 0).
// Note that at this point the length field of to_obj_array is not
// correct given that we are using it to keep track of the next
// start index. oop_iterate_range() (thankfully!) ignores the length
// field and only relies on the start / end parameters. It does
// however return the size of the object which will be incorrect. So
// we have to ignore it even if we wanted to use it.
to_obj_array->oop_iterate_range(&_scanner, start, end);
}

void G1ParScanThreadState::dispatch_task(ScannerTask task) {
@@ -411,10 +394,7 @@ oop G1ParScanThreadState::do_copy_to_survivor_space(G1HeapRegionAttr const regio
assert(region_attr.is_in_cset(),
"Unexpected region attr type: %s", region_attr.get_type_str());

// Get the klass once. We'll need it again later, and this avoids
// re-decoding when it's compressed.
Klass* klass = old->klass();
const size_t word_sz = old->size_given_klass(klass);
const size_t word_sz = old->size();

uint age = 0;
G1HeapRegionAttr dest_attr = next_region_attr(region_attr, old_mark, age);
@@ -481,20 +461,6 @@ oop G1ParScanThreadState::do_copy_to_survivor_space(G1HeapRegionAttr const regio
obj->set_mark_raw(old_mark);
}

// Most objects are not arrays, so do one array check rather than
// checking for each array category for each object.
if (klass->is_array_klass()) {
if (klass->is_objArray_klass()) {
start_partial_objarray(dest_attr, old, obj);
} else {
// Nothing needs to be done for typeArrays. Body doesn't contain
// any oops to scan, and the type in the klass will already be handled
// by processing the built-in module.
assert(klass->is_typeArray_klass(), "invariant");
}
return obj;
}

if (G1StringDedup::is_enabled()) {
const bool is_from_young = region_attr.is_young();
const bool is_to_young = dest_attr.is_young();
@@ -508,10 +474,17 @@ oop G1ParScanThreadState::do_copy_to_survivor_space(G1HeapRegionAttr const regio
obj);
}

G1ScanInYoungSetter x(&_scanner, dest_attr.is_young());
obj->oop_iterate_backwards(&_scanner);
if (obj->is_objArray() && arrayOop(obj)->length() >= ParGCArrayScanChunk) {
// We keep track of the next start index in the length field of
// the to-space object. The actual length can be found in the
// length field of the from-space object.
arrayOop(obj)->set_length(0);
do_partial_array(PartialArrayScanTask(old));
} else {
G1ScanInYoungSetter x(&_scanner, dest_attr.is_young());
obj->oop_iterate_backwards(&_scanner);
}
return obj;

} else {
_plab_allocator->undo_allocation(dest_attr, obj_ptr, word_sz, node_index);
return forward_ptr;
@@ -530,9 +503,7 @@ G1ParScanThreadState* G1ParScanThreadStateSet::state_for_worker(uint worker_id)
assert(worker_id < _n_workers, "out of bounds access");
if (_states[worker_id] == NULL) {
_states[worker_id] =
new G1ParScanThreadState(_g1h, _rdcqs,
worker_id, _n_workers,
_young_cset_length, _optional_cset_length);
new G1ParScanThreadState(_g1h, _rdcqs, worker_id, _young_cset_length, _optional_cset_length);
}
return _states[worker_id];
}
@@ -32,7 +32,6 @@
#include "gc/g1/g1RemSet.hpp"
#include "gc/g1/heapRegionRemSet.hpp"
#include "gc/shared/ageTable.hpp"
#include "gc/shared/partialArrayTaskStepper.hpp"
#include "gc/shared/taskqueue.hpp"
#include "memory/allocation.hpp"
#include "oops/oop.hpp"
@@ -80,9 +79,6 @@ class G1ParScanThreadState : public CHeapObj<mtGC> {
// Indicates whether in the last generation (old) there is no more space
// available for allocation.
bool _old_gen_is_full;
// Size (in elements) of a partial objArray task chunk.
int _partial_objarray_chunk_size;
PartialArrayTaskStepper _partial_array_stepper;

G1RedirtyCardsQueue& redirty_cards_queue() { return _rdcq; }
G1CardTable* ct() { return _ct; }
@@ -109,7 +105,6 @@ class G1ParScanThreadState : public CHeapObj<mtGC> {
G1ParScanThreadState(G1CollectedHeap* g1h,
G1RedirtyCardsQueueSet* rdcqs,
uint worker_id,
uint n_workers,
size_t young_cset_length,
size_t optional_cset_length);
virtual ~G1ParScanThreadState();
@@ -162,7 +157,6 @@ class G1ParScanThreadState : public CHeapObj<mtGC> {

private:
inline void do_partial_array(PartialArrayScanTask task);
inline void start_partial_objarray(G1HeapRegionAttr dest_dir, oop from, oop to);

HeapWord* allocate_copy_slow(G1HeapRegionAttr* dest_attr,
oop old,
@@ -255,6 +249,9 @@ class G1ParScanThreadStateSet : public StackObj {
G1ParScanThreadState* state_for_worker(uint worker_id);

const size_t* surviving_young_words() const;

private:
G1ParScanThreadState* new_par_scan_state(uint worker_id, size_t young_cset_length);
};

#endif // SHARE_GC_G1_G1PARSCANTHREADSTATE_HPP

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