void CompactibleSpace::initialize(MemRegion mr,
bool clear_space,
bool mangle_space) {
Space::initialize(mr, clear_space, mangle_space);
set_compaction_top(bottom());
_next_compaction_space = NULL;
}
void PSMarkSweepDecorator::precompact() {
// Reset our own compact top.
set_compaction_top(space()->bottom());
/* We allow some amount of garbage towards the bottom of the space, so
* we don't start compacting before there is a significant gain to be made.
* Occasionally, we want to ensure a full compaction, which is determined
* by the MarkSweepAlwaysCompactCount parameter. This is a significant
* performance improvement!
*/
bool skip_dead = ((PSMarkSweep::total_invocations() % MarkSweepAlwaysCompactCount) != 0);
size_t allowed_deadspace = 0;
if (skip_dead) {
const size_t ratio = allowed_dead_ratio();
allowed_deadspace = space()->capacity_in_words() * ratio / 100;
}
// Fetch the current destination decorator
PSMarkSweepDecorator* dest = destination_decorator();
ObjectStartArray* start_array = dest->start_array();
HeapWord* compact_top = dest->compaction_top();
HeapWord* compact_end = dest->space()->end();
HeapWord* q = space()->bottom();
HeapWord* t = space()->top();
HeapWord* end_of_live= q; /* One byte beyond the last byte of the last
live object. */
HeapWord* first_dead = space()->end(); /* The first dead object. */
LiveRange* liveRange = NULL; /* The current live range, recorded in the
first header of preceding free area. */
_first_dead = first_dead;
const intx interval = PrefetchScanIntervalInBytes;
while (q < t) {
assert(oop(q)->mark()->is_marked() || oop(q)->mark()->is_unlocked() ||
oop(q)->mark()->has_bias_pattern(),
"these are the only valid states during a mark sweep");
if (oop(q)->is_gc_marked()) {
/* prefetch beyond q */
Prefetch::write(q, interval);
size_t size = oop(q)->size();
size_t compaction_max_size = pointer_delta(compact_end, compact_top);
// This should only happen if a space in the young gen overflows the
// old gen. If that should happen, we null out the start_array, because
// the young spaces are not covered by one.
while(size > compaction_max_size) {
// First record the last compact_top
dest->set_compaction_top(compact_top);
// Advance to the next compaction decorator
advance_destination_decorator();
dest = destination_decorator();
// Update compaction info
start_array = dest->start_array();
compact_top = dest->compaction_top();
compact_end = dest->space()->end();
assert(compact_top == dest->space()->bottom(), "Advanced to space already in use");
assert(compact_end > compact_top, "Must always be space remaining");
compaction_max_size =
pointer_delta(compact_end, compact_top);
}
// store the forwarding pointer into the mark word
if (q != compact_top) {
oop(q)->forward_to(oop(compact_top));
assert(oop(q)->is_gc_marked(), "encoding the pointer should preserve the mark");
} else {
// if the object isn't moving we can just set the mark to the default
// mark and handle it specially later on.
oop(q)->init_mark();
assert(oop(q)->forwardee() == NULL, "should be forwarded to NULL");
}
// Update object start array
if (start_array) {
start_array->allocate_block(compact_top);
}
VALIDATE_MARK_SWEEP_ONLY(MarkSweep::register_live_oop(oop(q), size));
compact_top += size;
assert(compact_top <= dest->space()->end(),
"Exceeding space in destination");
q += size;
end_of_live = q;
} else {
/* run over all the contiguous dead objects */
HeapWord* end = q;
do {
/* prefetch beyond end */
Prefetch::write(end, interval);
end += oop(end)->size();
} while (end < t && (!oop(end)->is_gc_marked()));
/* see if we might want to pretend this object is alive so that
* we don't have to compact quite as often.
*/
if (allowed_deadspace > 0 && q == compact_top) {
size_t sz = pointer_delta(end, q);
if (insert_deadspace(allowed_deadspace, q, sz)) {
size_t compaction_max_size = pointer_delta(compact_end, compact_top);
// This should only happen if a space in the young gen overflows the
// old gen. If that should happen, we null out the start_array, because
// the young spaces are not covered by one.
while (sz > compaction_max_size) {
// First record the last compact_top
dest->set_compaction_top(compact_top);
// Advance to the next compaction decorator
advance_destination_decorator();
dest = destination_decorator();
// Update compaction info
start_array = dest->start_array();
compact_top = dest->compaction_top();
compact_end = dest->space()->end();
assert(compact_top == dest->space()->bottom(), "Advanced to space already in use");
assert(compact_end > compact_top, "Must always be space remaining");
compaction_max_size =
pointer_delta(compact_end, compact_top);
}
// store the forwarding pointer into the mark word
if (q != compact_top) {
oop(q)->forward_to(oop(compact_top));
assert(oop(q)->is_gc_marked(), "encoding the pointer should preserve the mark");
} else {
// if the object isn't moving we can just set the mark to the default
// mark and handle it specially later on.
oop(q)->init_mark();
assert(oop(q)->forwardee() == NULL, "should be forwarded to NULL");
}
// Update object start array
if (start_array) {
start_array->allocate_block(compact_top);
}
VALIDATE_MARK_SWEEP_ONLY(MarkSweep::register_live_oop(oop(q), sz));
compact_top += sz;
assert(compact_top <= dest->space()->end(),
"Exceeding space in destination");
q = end;
end_of_live = end;
continue;
}
}
/* for the previous LiveRange, record the end of the live objects. */
if (liveRange) {
liveRange->set_end(q);
}
/* record the current LiveRange object.
* liveRange->start() is overlaid on the mark word.
*/
liveRange = (LiveRange*)q;
liveRange->set_start(end);
liveRange->set_end(end);
/* see if this is the first dead region. */
if (q < first_dead) {
first_dead = q;
}
/* move on to the next object */
q = end;
}
}
assert(q == t, "just checking");
if (liveRange != NULL) {
liveRange->set_end(q);
}
_end_of_live = end_of_live;
if (end_of_live < first_dead) {
first_dead = end_of_live;
}
_first_dead = first_dead;
// Update compaction top
dest->set_compaction_top(compact_top);
}
