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6722116: CMS: Incorrect overflow handling when using parallel concurrent marking

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Fixed CMSConcMarkingTask::reset() to store the restart address upon a marking stack overflow and to use it as the base, suitably aligned, for restarting the scan in CMSConcMarkingTask::do_scan_and_mark().

Reviewed-by: jcoomes, tonyp
This commit is contained in:
Y. Srinivas Ramakrishna 2008-08-26 14:54:48 -07:00
parent befe056b42
commit aa6165d767
2 changed files with 69 additions and 37 deletions
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95
hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
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@ -3650,6 +3650,7 @@ class CMSConcMarkingTask: public YieldingFlexibleGangTask {
CompactibleFreeListSpace* _cms_space;
CompactibleFreeListSpace* _perm_space;
HeapWord* _global_finger;
HeapWord* _restart_addr;
// Exposed here for yielding support
Mutex* const _bit_map_lock;
@ -3680,7 +3681,7 @@ class CMSConcMarkingTask: public YieldingFlexibleGangTask {
_term.set_task(this);
assert(_cms_space->bottom() < _perm_space->bottom(),
"Finger incorrectly initialized below");
_global_finger = _cms_space->bottom();
_restart_addr = _global_finger = _cms_space->bottom();
}
@ -3698,6 +3699,10 @@ class CMSConcMarkingTask: public YieldingFlexibleGangTask {
bool result() { return _result; }
void reset(HeapWord* ra) {
assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
assert(ra < _perm_space->end(), "ra too large");
_restart_addr = _global_finger = ra;
_term.reset_for_reuse();
}
@ -3842,16 +3847,24 @@ void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
int n_tasks = pst->n_tasks();
// We allow that there may be no tasks to do here because
// we are restarting after a stack overflow.
assert(pst->valid() || n_tasks == 0, "Uninitializd use?");
assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
int nth_task = 0;
HeapWord* start = sp->bottom();
HeapWord* aligned_start = sp->bottom();
if (sp->used_region().contains(_restart_addr)) {
// Align down to a card boundary for the start of 0th task
// for this space.
aligned_start =
(HeapWord*)align_size_down((uintptr_t)_restart_addr,
CardTableModRefBS::card_size);
}
size_t chunk_size = sp->marking_task_size();
while (!pst->is_task_claimed(/* reference */ nth_task)) {
// Having claimed the nth task in this space,
// compute the chunk that it corresponds to:
MemRegion span = MemRegion(start + nth_task*chunk_size,
start + (nth_task+1)*chunk_size);
MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
aligned_start + (nth_task+1)*chunk_size);
// Try and bump the global finger via a CAS;
// note that we need to do the global finger bump
// _before_ taking the intersection below, because
@ -3866,26 +3879,40 @@ void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
// beyond the "top" address of the space.
span = span.intersection(sp->used_region());
if (!span.is_empty()) { // Non-null task
// We want to skip the first object because
// the protocol is to scan any object in its entirety
// that _starts_ in this span; a fortiori, any
// object starting in an earlier span is scanned
// as part of an earlier claimed task.
// Below we use the "careful" version of block_start
// so we do not try to navigate uninitialized objects.
HeapWord* prev_obj = sp->block_start_careful(span.start());
// Below we use a variant of block_size that uses the
// Printezis bits to avoid waiting for allocated
// objects to become initialized/parsable.
while (prev_obj < span.start()) {
size_t sz = sp->block_size_no_stall(prev_obj, _collector);
if (sz > 0) {
prev_obj += sz;
HeapWord* prev_obj;
assert(!span.contains(_restart_addr) || nth_task == 0,
"Inconsistency");
if (nth_task == 0) {
// For the 0th task, we'll not need to compute a block_start.
if (span.contains(_restart_addr)) {
// In the case of a restart because of stack overflow,
// we might additionally skip a chunk prefix.
prev_obj = _restart_addr;
} else {
// In this case we may end up doing a bit of redundant
// scanning, but that appears unavoidable, short of
// locking the free list locks; see bug 6324141.
break;
prev_obj = span.start();
}
} else {
// We want to skip the first object because
// the protocol is to scan any object in its entirety
// that _starts_ in this span; a fortiori, any
// object starting in an earlier span is scanned
// as part of an earlier claimed task.
// Below we use the "careful" version of block_start
// so we do not try to navigate uninitialized objects.
prev_obj = sp->block_start_careful(span.start());
// Below we use a variant of block_size that uses the
// Printezis bits to avoid waiting for allocated
// objects to become initialized/parsable.
while (prev_obj < span.start()) {
size_t sz = sp->block_size_no_stall(prev_obj, _collector);
if (sz > 0) {
prev_obj += sz;
} else {
// In this case we may end up doing a bit of redundant
// scanning, but that appears unavoidable, short of
// locking the free list locks; see bug 6324141.
break;
}
}
}
if (prev_obj < span.end()) {
@ -3938,12 +3965,14 @@ class Par_ConcMarkingClosure: public OopClosure {
void handle_stack_overflow(HeapWord* lost);
};
// Grey object rescan during work stealing phase --
// the salient assumption here is that stolen oops must
// always be initialized, so we do not need to check for
// uninitialized objects before scanning here.
// Grey object scanning during work stealing phase --
// the salient assumption here is that any references
// that are in these stolen objects being scanned must
// already have been initialized (else they would not have
// been published), so we do not need to check for
// uninitialized objects before pushing here.
void Par_ConcMarkingClosure::do_oop(oop obj) {
assert(obj->is_oop_or_null(), "expected an oop or NULL");
assert(obj->is_oop_or_null(true), "expected an oop or NULL");
HeapWord* addr = (HeapWord*)obj;
// Check if oop points into the CMS generation
// and is not marked
@ -4001,7 +4030,7 @@ void Par_ConcMarkingClosure::trim_queue(size_t max) {
// in CMSCollector's _restart_address.
void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
// We need to do this under a mutex to prevent other
// workers from interfering with the expansion below.
// workers from interfering with the work done below.
MutexLockerEx ml(_overflow_stack->par_lock(),
Mutex::_no_safepoint_check_flag);
// Remember the least grey address discarded
@ -6554,7 +6583,7 @@ void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
if (obj != NULL) {
// Ignore mark word because this could be an already marked oop
// that may be chained at the end of the overflow list.
assert(obj->is_oop(), "expected an oop");
assert(obj->is_oop(true), "expected an oop");
HeapWord* addr = (HeapWord*)obj;
if (_span.contains(addr) &&
!_bit_map->isMarked(addr)) {
@ -7289,6 +7318,8 @@ Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
_should_remember_klasses(collector->should_unload_classes())
{ }
// Assumes thread-safe access by callers, who are
// responsible for mutual exclusion.
void CMSCollector::lower_restart_addr(HeapWord* low) {
assert(_span.contains(low), "Out of bounds addr");
if (_restart_addr == NULL) {
@ -7314,7 +7345,7 @@ void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
// in CMSCollector's _restart_address.
void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
// We need to do this under a mutex to prevent other
// workers from interfering with the expansion below.
// workers from interfering with the work done below.
MutexLockerEx ml(_overflow_stack->par_lock(),
Mutex::_no_safepoint_check_flag);
// Remember the least grey address discarded