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Unconditionally preserve all marks during GC #6

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@@ -3061,7 +3061,7 @@ void G1CollectedHeap::do_collection_pause_at_safepoint_helper(double target_paus

void G1CollectedHeap::preserve_mark_during_evac_failure(uint worker_id, oop obj, markWord m) {
_preserved_marks_set.get(worker_id)->push_if_necessary(obj, m);
_preserved_marks_set.get(worker_id)->push(obj, m);

bool G1ParEvacuateFollowersClosure::offer_termination() {
@@ -113,14 +113,6 @@ void G1FullGCCompactionPoint::forward(oop object, size_t size) {
// even if the mark-word is used. This is no problem since
// forwardee() will return NULL in the compaction phase as well.
} else {
// Make sure object has the correct mark-word set or that it will be
// fixed when restoring the preserved marks.
assert(object->mark() == markWord::prototype_for_klass(object->klass()) || // Correct mark
object->mark_must_be_preserved() || // Will be restored by PreservedMarksSet
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(UseBiasedLocking && object->has_bias_pattern()), // Will be restored by BiasedLocking
"should have correct prototype obj: " PTR_FORMAT " mark: " PTR_FORMAT " prototype: " PTR_FORMAT,
p2i(object), object->mark().value(), markWord::prototype_for_klass(object->klass()).value());
assert(object->forwardee() == NULL, "should be forwarded to NULL");
@@ -54,10 +54,9 @@ inline bool G1FullGCMarker::mark_object(oop obj) {

// Marked by us, preserve if needed.
markWord mark = obj->mark();
if (obj->mark_must_be_preserved(mark) &&
// It is not necessary to preserve marks for objects in regions we do not
// compact because we do not change their headers (i.e. forward them).
_collector->is_compacting(obj)) {
// It is not necessary to preserve marks for objects in regions we do not
// compact because we do not change their headers (i.e. forward them).
if (_collector->is_compacting(obj)) {
preserved_stack()->push(obj, mark);

@@ -79,11 +79,6 @@ template <class T> inline void G1AdjustClosure::adjust_pointer(T* p) {
oop forwardee = obj->forwardee();
if (forwardee == NULL) {
// Not forwarded, return current reference.
assert(obj->mark() == markWord::prototype_for_klass(obj->klass()) || // Correct mark
obj->mark_must_be_preserved() || // Will be restored by PreservedMarksSet
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(UseBiasedLocking && obj->has_bias_pattern()), // Will be restored by BiasedLocking
"Must have correct prototype or be preserved, obj: " PTR_FORMAT ", mark: " PTR_FORMAT ", prototype: " PTR_FORMAT,
p2i(obj), obj->mark().value(), markWord::prototype_for_klass(obj->klass()).value());

@@ -360,7 +360,7 @@ oop PSPromotionManager::oop_promotion_failed(oop obj, markWord obj_mark) {


_preserved_marks->push_if_necessary(obj, obj_mark);
_preserved_marks->push(obj, obj_mark);
} else {
// We lost, someone else "owns" this object
guarantee(obj->is_forwarded(), "Object must be forwarded if the cas failed.");
@@ -680,7 +680,7 @@ void DefNewGeneration::handle_promotion_failure(oop old) {

_promotion_failed = true;
_preserved_marks_set.get()->push_if_necessary(old, old->mark());
_preserved_marks_set.get()->push(old, old->mark());
// forward to self

@@ -41,9 +41,7 @@ inline void MarkSweep::mark_object(oop obj) {
markWord mark = obj->mark();

if (obj->mark_must_be_preserved(mark)) {
preserve_mark(obj, mark);
preserve_mark(obj, mark);

template <class T> inline void MarkSweep::mark_and_push(T* p) {
@@ -52,12 +52,9 @@ class PreservedMarks {

OopAndMarkWordStack _stack;

inline bool should_preserve_mark(oop obj, markWord m) const;

size_t size() const { return _stack.size(); }
inline void push(oop obj, markWord m);
inline void push_if_necessary(oop obj, markWord m);
// Iterate over the stack, restore all preserved marks, and
// reclaim the memory taken up by the stack segments.
void restore();
@@ -30,22 +30,11 @@
#include "oops/oop.inline.hpp"
#include "utilities/stack.inline.hpp"

inline bool PreservedMarks::should_preserve_mark(oop obj, markWord m) const {
return obj->mark_must_be_preserved_for_promotion_failure(m);

inline void PreservedMarks::push(oop obj, markWord m) {
assert(should_preserve_mark(obj, m), "pre-condition");
OopAndMarkWord elem(obj, m);

inline void PreservedMarks::push_if_necessary(oop obj, markWord m) {
if (should_preserve_mark(obj, m)) {
push(obj, m);

inline void PreservedMarks::init_forwarded_mark(oop obj) {
@@ -360,7 +360,7 @@ class ShenandoahPrepareForCompactionObjectClosure : public ObjectClosure {
// Object fits into current region, record new location:
assert(_compact_point + obj_size <= _to_region->end(), "must fit");
shenandoah_assert_not_forwarded(NULL, p);
_preserved_marks->push_if_necessary(p, p->mark());
_preserved_marks->push(p, p->mark());
_compact_point += obj_size;
@@ -468,7 +468,7 @@ void ShenandoahFullGC::calculate_target_humongous_objects() {

if (start >= to_begin && start != r->index()) {
// Fits into current window, and the move is non-trivial. Record the move then, and continue scan.
_preserved_marks->get(0)->push_if_necessary(old_obj, old_obj->mark());
_preserved_marks->get(0)->push(old_obj, old_obj->mark());
to_end = start;
@@ -236,30 +236,6 @@ class markWord {
// is transient and *should* be short-lived).
static markWord INFLATING() { return zero(); } // inflate-in-progress

// Should this header be preserved during GC?
template <typename KlassProxy>
inline bool must_be_preserved(KlassProxy klass) const;

// Should this header (including its age bits) be preserved in the
// case of a promotion failure during scavenge?
// Note that we special case this situation. We want to avoid
// calling BiasedLocking::preserve_marks()/restore_marks() (which
// decrease the number of mark words that need to be preserved
// during GC) during each scavenge. During scavenges in which there
// is no promotion failure, we actually don't need to call the above
// routines at all, since we don't mutate and re-initialize the
// marks of promoted objects using init_mark(). However, during
// scavenges which result in promotion failure, we do re-initialize
// the mark words of objects, meaning that we should have called
// these mark word preservation routines. Currently there's no good
// place in which to call them in any of the scavengers (although
// guarded by appropriate locks we could make one), but the
// observation is that promotion failures are quite rare and
// reducing the number of mark words preserved during them isn't a
// high priority.
template <typename KlassProxy>
inline bool must_be_preserved_for_promotion_failure(KlassProxy klass) const;

// WARNING: The following routines are used EXCLUSIVELY by
// synchronization functions. They are not really gc safe.
// They must get updated if markWord layout get changed.
@@ -29,45 +29,6 @@
#include "oops/markWord.hpp"
#include "runtime/globals.hpp"

// Should this header be preserved during GC?
template <typename KlassProxy>
inline bool markWord::must_be_preserved(KlassProxy klass) const {
if (UseBiasedLocking) {
if (has_bias_pattern()) {
// Will reset bias at end of collection
// Mark words of biased and currently locked objects are preserved separately
return false;
markWord prototype_header = prototype_for_klass(klass);
if (prototype_header.has_bias_pattern()) {
// Individual instance which has its bias revoked; must return
// true for correctness
return true;
return (!is_unlocked() || !has_no_hash());

// Should this header be preserved in the case of a promotion failure during scavenge?
template <typename KlassProxy>
inline bool markWord::must_be_preserved_for_promotion_failure(KlassProxy klass) const {
if (UseBiasedLocking) {
// We don't explicitly save off the mark words of biased and
// currently-locked objects during scavenges, so if during a
// promotion failure we encounter either a biased mark word or a
// klass which still has a biasable prototype header, we have to
// preserve the mark word. This results in oversaving, but promotion
// failures are rare, and this avoids adding more complex logic to
// the scavengers to call new variants of
// BiasedLocking::preserve_marks() / restore_marks() in the middle
// of a scavenge when a promotion failure has first been detected.
if (has_bias_pattern() || prototype_for_klass(klass).has_bias_pattern()) {
return true;
return (!is_unlocked() || !has_no_hash());

inline markWord markWord::prototype_for_klass(const Klass* klass) {
markWord prototype_header = klass->prototype_header();
assert(prototype_header == prototype() || prototype_header.has_bias_pattern(), "corrupt prototype header");
@@ -294,11 +294,6 @@ class oopDesc {
inline markWord displaced_mark() const;
inline void set_displaced_mark(markWord m);

// Checks if the mark word needs to be preserved
inline bool mark_must_be_preserved() const;
inline bool mark_must_be_preserved(markWord m) const;
inline bool mark_must_be_preserved_for_promotion_failure(markWord m) const;

static bool has_klass_gap();

// for code generation
@@ -409,21 +409,4 @@ class DeferredObjectToKlass {

bool oopDesc::mark_must_be_preserved() const {
return mark_must_be_preserved(mark());

bool oopDesc::mark_must_be_preserved(markWord m) const {
// There's a circular dependency between oop.inline.hpp and
// markWord.inline.hpp because markWord::must_be_preserved wants to call
// oopDesc::klass(). This could be solved by calling klass() here. However,
// not all paths inside must_be_preserved calls klass(). Defer the call until
// the klass is actually needed.
return m.must_be_preserved(DeferredObjectToKlass(this));

bool oopDesc::mark_must_be_preserved_for_promotion_failure(markWord m) const {
return m.must_be_preserved_for_promotion_failure(DeferredObjectToKlass(this));

@@ -1441,10 +1441,8 @@ inline void ObjectMarker::mark(oop o) {
// object's mark word
markWord mark = o->mark();

if (o->mark_must_be_preserved(mark)) {

// mark the object