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8073321: assert(q > prev_q) failed: we should be moving forward through memory

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Reviewed-by: jmasa, mgerdin
This commit is contained in:
Bengt Rutisson 2016-04-14 11:17:34 +02:00
parent 8e65d33717
commit 3bb96580fb
4 changed files with 194 additions and 187 deletions

2
hotspot/src/share/vm/gc/cms/compactibleFreeListSpace.hpp

@ -82,6 +82,8 @@ class CompactibleFreeListSpace: public CompactibleSpace {
template <typename SpaceType>
friend void CompactibleSpace::scan_and_compact(SpaceType* space);
template <typename SpaceType>
friend void CompactibleSpace::verify_up_to_first_dead(SpaceType* space);
template <typename SpaceType>
friend void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp);
// "Size" of chunks of work (executed during parallel remark phases

16
hotspot/src/share/vm/gc/shared/space.cpp

@ -411,22 +411,6 @@ HeapWord* CompactibleSpace::forward(oop q, size_t size,
return compact_top;
}
bool CompactibleSpace::insert_deadspace(size_t& allowed_deadspace_words,
HeapWord* q, size_t deadlength) {
if (allowed_deadspace_words >= deadlength) {
allowed_deadspace_words -= deadlength;
CollectedHeap::fill_with_object(q, deadlength);
oop(q)->set_mark(oop(q)->mark()->set_marked());
assert((int) deadlength == oop(q)->size(), "bad filler object size");
// Recall that we required "q == compaction_top".
return true;
} else {
allowed_deadspace_words = 0;
return false;
}
}
void ContiguousSpace::prepare_for_compaction(CompactPoint* cp) {
scan_and_forward(this, cp);
}

16
hotspot/src/share/vm/gc/shared/space.hpp

@ -362,6 +362,12 @@ private:
inline size_t obj_size(const HeapWord* addr) const;
template <class SpaceType>
static inline void verify_up_to_first_dead(SpaceType* space) NOT_DEBUG_RETURN;
template <class SpaceType>
static inline void clear_empty_region(SpaceType* space);
public:
CompactibleSpace() :
_compaction_top(NULL), _next_compaction_space(NULL) {}
@ -455,16 +461,6 @@ protected:
return end();
}
// Requires "allowed_deadspace_words > 0", that "q" is the start of a
// free block of the given "word_len", and that "q", were it an object,
// would not move if forwarded. If the size allows, fill the free
// block with an object, to prevent excessive compaction. Returns "true"
// iff the free region was made deadspace, and modifies
// "allowed_deadspace_words" to reflect the number of available deadspace
// words remaining after this operation.
bool insert_deadspace(size_t& allowed_deadspace_words, HeapWord* q,
size_t word_len);
// Below are template functions for scan_and_* algorithms (avoiding virtual calls).
// The space argument should be a subclass of CompactibleSpace, implementing
// scan_limit(), scanned_block_is_obj(), and scanned_block_size(),

347
hotspot/src/share/vm/gc/shared/space.inline.hpp

@ -31,6 +31,7 @@
#include "gc/shared/space.hpp"
#include "gc/shared/spaceDecorator.hpp"
#include "memory/universe.hpp"
#include "oops/oopsHierarchy.hpp"
#include "runtime/prefetch.inline.hpp"
#include "runtime/safepoint.hpp"
@ -75,11 +76,61 @@ size_t CompactibleSpace::obj_size(const HeapWord* addr) const {
return oop(addr)->size();
}
class DeadSpacer : StackObj {
size_t _allowed_deadspace_words;
bool _active;
CompactibleSpace* _space;
public:
DeadSpacer(CompactibleSpace* space) : _space(space), _allowed_deadspace_words(0) {
size_t ratio = _space->allowed_dead_ratio();
_active = ratio > 0;
if (_active) {
assert(!UseG1GC, "G1 should not be using dead space");
// 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.
if ((MarkSweep::total_invocations() % MarkSweepAlwaysCompactCount) != 0) {
_allowed_deadspace_words = (space->capacity() * ratio / 100) / HeapWordSize;
} else {
_active = false;
}
}
}
bool insert_deadspace(HeapWord* dead_start, HeapWord* dead_end) {
if (!_active) {
return false;
}
size_t dead_length = pointer_delta(dead_end, dead_start);
if (_allowed_deadspace_words >= dead_length) {
_allowed_deadspace_words -= dead_length;
CollectedHeap::fill_with_object(dead_start, dead_length);
oop obj = oop(dead_start);
obj->set_mark(obj->mark()->set_marked());
assert(dead_length == (size_t)obj->size(), "bad filler object size");
log_develop_trace(gc, compaction)("Inserting object to dead space: " PTR_FORMAT ", " PTR_FORMAT ", " SIZE_FORMAT "b",
p2i(dead_start), p2i(dead_end), dead_length * HeapWordSize);
return true;
} else {
_active = false;
return false;
}
}
};
template <class SpaceType>
inline void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp) {
// Compute the new addresses for the live objects and store it in the mark
// Used by universe::mark_sweep_phase2()
HeapWord* compact_top; // This is where we are currently compacting to.
// We're sure to be here before any objects are compacted into this
// space, so this is a good time to initialize this:
@ -90,89 +141,73 @@ inline void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* c
assert(cp->threshold == NULL, "just checking");
assert(cp->gen->first_compaction_space() == space, "just checking");
cp->space = cp->gen->first_compaction_space();
compact_top = cp->space->bottom();
cp->space->set_compaction_top(compact_top);
cp->threshold = cp->space->initialize_threshold();
} else {
compact_top = cp->space->compaction_top();
cp->space->set_compaction_top(cp->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.
uint invocations = MarkSweep::total_invocations();
bool skip_dead = ((invocations % MarkSweepAlwaysCompactCount) != 0);
HeapWord* compact_top = cp->space->compaction_top(); // This is where we are currently compacting to.
size_t allowed_deadspace = 0;
if (skip_dead) {
const size_t ratio = space->allowed_dead_ratio();
allowed_deadspace = (space->capacity() * ratio / 100) / HeapWordSize;
}
DeadSpacer dead_spacer(space);
HeapWord* q = space->bottom();
HeapWord* t = space->scan_limit();
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.
HeapWord* end_of_live = space->bottom(); // One byte beyond the last byte of the last live object.
HeapWord* first_dead = NULL; // The first dead object.
const intx interval = PrefetchScanIntervalInBytes;
while (q < t) {
assert(!space->scanned_block_is_obj(q) ||
oop(q)->mark()->is_marked() || oop(q)->mark()->is_unlocked() ||
oop(q)->mark()->has_bias_pattern(),
HeapWord* cur_obj = space->bottom();
HeapWord* scan_limit = space->scan_limit();
while (cur_obj < scan_limit) {
assert(!space->scanned_block_is_obj(cur_obj) ||
oop(cur_obj)->mark()->is_marked() || oop(cur_obj)->mark()->is_unlocked() ||
oop(cur_obj)->mark()->has_bias_pattern(),
"these are the only valid states during a mark sweep");
if (space->scanned_block_is_obj(q) && oop(q)->is_gc_marked()) {
// prefetch beyond q
Prefetch::write(q, interval);
size_t size = space->scanned_block_size(q);
compact_top = cp->space->forward(oop(q), size, cp, compact_top);
q += size;
end_of_live = q;
if (space->scanned_block_is_obj(cur_obj) && oop(cur_obj)->is_gc_marked()) {
// prefetch beyond cur_obj
Prefetch::write(cur_obj, interval);
size_t size = space->scanned_block_size(cur_obj);
compact_top = cp->space->forward(oop(cur_obj), size, cp, compact_top);
cur_obj += size;
end_of_live = cur_obj;
} else {
// run over all the contiguous dead objects
HeapWord* end = q;
HeapWord* end = cur_obj;
do {
// prefetch beyond end
Prefetch::write(end, interval);
end += space->scanned_block_size(end);
} while (end < t && (!space->scanned_block_is_obj(end) || !oop(end)->is_gc_marked()));
} while (end < scan_limit && (!space->scanned_block_is_obj(end) || !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 (space->insert_deadspace(allowed_deadspace, q, sz)) {
compact_top = cp->space->forward(oop(q), sz, cp, compact_top);
q = end;
end_of_live = end;
continue;
if (cur_obj == compact_top && dead_spacer.insert_deadspace(cur_obj, end)) {
oop obj = oop(cur_obj);
compact_top = cp->space->forward(obj, obj->size(), cp, compact_top);
end_of_live = end;
} else {
// otherwise, it really is a free region.
// cur_obj is a pointer to a dead object. Use this dead memory to store a pointer to the next live object.
*(HeapWord**)cur_obj = end;
// see if this is the first dead region.
if (first_dead == NULL) {
first_dead = cur_obj;
}
}
// otherwise, it really is a free region.
// q is a pointer to a dead object. Use this dead memory to store a pointer to the next live object.
(*(HeapWord**)q) = end;
// see if this is the first dead region.
if (q < first_dead) {
first_dead = q;
}
// move on to the next object
q = end;
cur_obj = end;
}
}
assert(q == t, "just checking");
assert(cur_obj == scan_limit, "just checking");
space->_end_of_live = end_of_live;
if (end_of_live < first_dead) {
first_dead = end_of_live;
if (first_dead != NULL) {
space->_first_dead = first_dead;
} else {
space->_first_dead = end_of_live;
}
space->_first_dead = first_dead;
// save the compaction_top of the compaction space.
cp->space->set_compaction_top(compact_top);
@ -183,127 +218,58 @@ inline void CompactibleSpace::scan_and_adjust_pointers(SpaceType* space) {
// adjust all the interior pointers to point at the new locations of objects
// Used by MarkSweep::mark_sweep_phase3()
HeapWord* q = space->bottom();
HeapWord* t = space->_end_of_live; // Established by "prepare_for_compaction".
HeapWord* cur_obj = space->bottom();
HeapWord* const end_of_live = space->_end_of_live; // Established by "scan_and_forward".
HeapWord* const first_dead = space->_first_dead; // Established by "scan_and_forward".
assert(space->_first_dead <= space->_end_of_live, "Stands to reason, no?");
if (q < t && space->_first_dead > q && !oop(q)->is_gc_marked()) {
// we have a chunk of the space which hasn't moved and we've
// reinitialized the mark word during the previous pass, so we can't
// use is_gc_marked for the traversal.
HeapWord* end = space->_first_dead;
while (q < end) {
// I originally tried to conjoin "block_start(q) == q" to the
// assertion below, but that doesn't work, because you can't
// accurately traverse previous objects to get to the current one
// after their pointers have been
// updated, until the actual compaction is done. dld, 4/00
assert(space->block_is_obj(q), "should be at block boundaries, and should be looking at objs");
// point all the oops to the new location
size_t size = MarkSweep::adjust_pointers(oop(q));
size = space->adjust_obj_size(size);
q += size;
}
if (space->_first_dead == t) {
q = t;
} else {
// The first dead object is no longer an object. At that memory address,
// there is a pointer to the first live object that the previous phase found.
q = *((HeapWord**)(space->_first_dead));
}
}
assert(first_dead <= end_of_live, "Stands to reason, no?");
const intx interval = PrefetchScanIntervalInBytes;
debug_only(HeapWord* prev_q = NULL);
while (q < t) {
// prefetch beyond q
Prefetch::write(q, interval);
if (oop(q)->is_gc_marked()) {
// q is alive
debug_only(HeapWord* prev_obj = NULL);
while (cur_obj < end_of_live) {
Prefetch::write(cur_obj, interval);
if (cur_obj < first_dead || oop(cur_obj)->is_gc_marked()) {
// cur_obj is alive
// point all the oops to the new location
size_t size = MarkSweep::adjust_pointers(oop(q));
size_t size = MarkSweep::adjust_pointers(oop(cur_obj));
size = space->adjust_obj_size(size);
debug_only(prev_q = q);
q += size;
debug_only(prev_obj = cur_obj);
cur_obj += size;
} else {
debug_only(prev_q = q);
// q is not a live object, instead it points at the next live object
q = *(HeapWord**)q;
assert(q > prev_q, "we should be moving forward through memory, q: " PTR_FORMAT ", prev_q: " PTR_FORMAT, p2i(q), p2i(prev_q));
debug_only(prev_obj = cur_obj);
// cur_obj is not a live object, instead it points at the next live object
cur_obj = *(HeapWord**)cur_obj;
assert(cur_obj > prev_obj, "we should be moving forward through memory, cur_obj: " PTR_FORMAT ", prev_obj: " PTR_FORMAT, p2i(cur_obj), p2i(prev_obj));
}
}
assert(q == t, "just checking");
assert(cur_obj == end_of_live, "just checking");
}
#ifdef ASSERT
template <class SpaceType>
inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
// Copy all live objects to their new location
// Used by MarkSweep::mark_sweep_phase4()
inline void CompactibleSpace::verify_up_to_first_dead(SpaceType* space) {
HeapWord* cur_obj = space->bottom();
HeapWord* q = space->bottom();
HeapWord* const t = space->_end_of_live;
debug_only(HeapWord* prev_q = NULL);
if (cur_obj < space->_end_of_live && space->_first_dead > cur_obj && !oop(cur_obj)->is_gc_marked()) {
// we have a chunk of the space which hasn't moved and we've reinitialized
// the mark word during the previous pass, so we can't use is_gc_marked for
// the traversal.
HeapWord* prev_obj = NULL;
if (q < t && space->_first_dead > q && !oop(q)->is_gc_marked()) {
#ifdef ASSERT // Debug only
// we have a chunk of the space which hasn't moved and we've reinitialized
// the mark word during the previous pass, so we can't use is_gc_marked for
// the traversal.
HeapWord* const end = space->_first_dead;
while (q < end) {
size_t size = space->obj_size(q);
assert(!oop(q)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
prev_q = q;
q += size;
}
#endif
if (space->_first_dead == t) {
q = t;
} else {
// $$$ Funky
q = (HeapWord*) oop(space->_first_dead)->mark()->decode_pointer();
}
}
const intx scan_interval = PrefetchScanIntervalInBytes;
const intx copy_interval = PrefetchCopyIntervalInBytes;
while (q < t) {
if (!oop(q)->is_gc_marked()) {
// mark is pointer to next marked oop
debug_only(prev_q = q);
q = (HeapWord*) oop(q)->mark()->decode_pointer();
assert(q > prev_q, "we should be moving forward through memory");
} else {
// prefetch beyond q
Prefetch::read(q, scan_interval);
// size and destination
size_t size = space->obj_size(q);
HeapWord* compaction_top = (HeapWord*)oop(q)->forwardee();
// prefetch beyond compaction_top
Prefetch::write(compaction_top, copy_interval);
// copy object and reinit its mark
assert(q != compaction_top, "everything in this pass should be moving");
Copy::aligned_conjoint_words(q, compaction_top, size);
oop(compaction_top)->init_mark();
assert(oop(compaction_top)->klass() != NULL, "should have a class");
debug_only(prev_q = q);
q += size;
}
while (cur_obj < space->_first_dead) {
size_t size = space->obj_size(cur_obj);
assert(!oop(cur_obj)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
prev_obj = cur_obj;
cur_obj += size;
}
}
}
#endif
template <class SpaceType>
inline void CompactibleSpace::clear_empty_region(SpaceType* space) {
// Let's remember if we were empty before we did the compaction.
bool was_empty = space->used_region().is_empty();
// Reset space after compaction is complete
@ -320,6 +286,65 @@ inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
}
}
template <class SpaceType>
inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
// Copy all live objects to their new location
// Used by MarkSweep::mark_sweep_phase4()
verify_up_to_first_dead(space);
HeapWord* const end_of_live = space->_end_of_live;
assert(space->_first_dead <= end_of_live, "Invariant. _first_dead: " PTR_FORMAT " <= end_of_live: " PTR_FORMAT, p2i(space->_first_dead), p2i(end_of_live));
if (space->_first_dead == end_of_live && !oop(space->bottom())->is_gc_marked()) {
// Nothing to compact. The space is either empty or all live object should be left in place.
clear_empty_region(space);
return;
}
const intx scan_interval = PrefetchScanIntervalInBytes;
const intx copy_interval = PrefetchCopyIntervalInBytes;
assert(space->bottom() < end_of_live, "bottom: " PTR_FORMAT " should be < end_of_live: " PTR_FORMAT, p2i(space->bottom()), p2i(end_of_live));
HeapWord* cur_obj = space->bottom();
if (space->_first_dead > cur_obj && !oop(cur_obj)->is_gc_marked()) {
// All object before _first_dead can be skipped. They should not be moved.
// A pointer to the first live object is stored at the memory location for _first_dead.
cur_obj = *(HeapWord**)(space->_first_dead);
}
debug_only(HeapWord* prev_obj = NULL);
while (cur_obj < end_of_live) {
if (!oop(cur_obj)->is_gc_marked()) {
debug_only(prev_obj = cur_obj);
// The first word of the dead object contains a pointer to the next live object or end of space.
cur_obj = *(HeapWord**)cur_obj;
assert(cur_obj > prev_obj, "we should be moving forward through memory");
} else {
// prefetch beyond q
Prefetch::read(cur_obj, scan_interval);
// size and destination
size_t size = space->obj_size(cur_obj);
HeapWord* compaction_top = (HeapWord*)oop(cur_obj)->forwardee();
// prefetch beyond compaction_top
Prefetch::write(compaction_top, copy_interval);
// copy object and reinit its mark
assert(cur_obj != compaction_top, "everything in this pass should be moving");
Copy::aligned_conjoint_words(cur_obj, compaction_top, size);
oop(compaction_top)->init_mark();
assert(oop(compaction_top)->klass() != NULL, "should have a class");
debug_only(prev_obj = cur_obj);
cur_obj += size;
}
}
clear_empty_region(space);
}
size_t ContiguousSpace::scanned_block_size(const HeapWord* addr) const {
return oop(addr)->size();
}