/*
* Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#include "precompiled.hpp"
#include "gc/parallel/objectStartArray.inline.hpp"
#include "gc/parallel/parallelScavengeHeap.inline.hpp"
#include "gc/parallel/psCardTable.hpp"
#include "gc/parallel/psPromotionManager.inline.hpp"
#include "gc/parallel/psScavenge.inline.hpp"
#include "gc/parallel/psYoungGen.hpp"
#include "memory/iterator.inline.hpp"
#include "oops/access.inline.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/prefetch.inline.hpp"
#include "utilities/align.hpp"
// Checks an individual oop for missing precise marks. Mark
// may be either dirty or newgen.
class CheckForUnmarkedOops : public BasicOopIterateClosure {
private:
PSYoungGen* _young_gen;
PSCardTable* _card_table;
HeapWord* _unmarked_addr;
protected:
template <class T> void do_oop_work(T* p) {
oop obj = RawAccess<>::oop_load(p);
if (_young_gen->is_in_reserved(obj) &&
!_card_table->addr_is_marked_imprecise(p)) {
// Don't overwrite the first missing card mark
if (_unmarked_addr == NULL) {
_unmarked_addr = (HeapWord*)p;
}
}
}
public:
CheckForUnmarkedOops(PSYoungGen* young_gen, PSCardTable* card_table) :
_young_gen(young_gen), _card_table(card_table), _unmarked_addr(NULL) { }
virtual void do_oop(oop* p) { CheckForUnmarkedOops::do_oop_work(p); }
virtual void do_oop(narrowOop* p) { CheckForUnmarkedOops::do_oop_work(p); }
bool has_unmarked_oop() {
return _unmarked_addr != NULL;
}
};
// Checks all objects for the existence of some type of mark,
// precise or imprecise, dirty or newgen.
class CheckForUnmarkedObjects : public ObjectClosure {
private:
PSYoungGen* _young_gen;
PSCardTable* _card_table;
public:
CheckForUnmarkedObjects() {
ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
_young_gen = heap->young_gen();
_card_table = heap->card_table();
}
// Card marks are not precise. The current system can leave us with
// a mismatch of precise marks and beginning of object marks. This means
// we test for missing precise marks first. If any are found, we don't
// fail unless the object head is also unmarked.
virtual void do_object(oop obj) {
CheckForUnmarkedOops object_check(_young_gen, _card_table);
obj->oop_iterate(&object_check);
if (object_check.has_unmarked_oop()) {
guarantee(_card_table->addr_is_marked_imprecise(obj), "Found unmarked young_gen object");
}
}
};
// Checks for precise marking of oops as newgen.
class CheckForPreciseMarks : public BasicOopIterateClosure {
private:
PSYoungGen* _young_gen;
PSCardTable* _card_table;
protected:
template <class T> void do_oop_work(T* p) {
oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);
if (_young_gen->is_in_reserved(obj)) {
assert(_card_table->addr_is_marked_precise(p), "Found unmarked precise oop");
_card_table->set_card_newgen(p);
}
}
public:
CheckForPreciseMarks(PSYoungGen* young_gen, PSCardTable* card_table) :
_young_gen(young_gen), _card_table(card_table) { }
virtual void do_oop(oop* p) { CheckForPreciseMarks::do_oop_work(p); }
virtual void do_oop(narrowOop* p) { CheckForPreciseMarks::do_oop_work(p); }
};
// We get passed the space_top value to prevent us from traversing into
// the old_gen promotion labs, which cannot be safely parsed.
// Do not call this method if the space is empty.
// It is a waste to start tasks and get here only to
// do no work. If this method needs to be called
// when the space is empty, fix the calculation of
// end_card to allow sp_top == sp->bottom().
// The generation (old gen) is divided into slices, which are further
// subdivided into stripes, with one stripe per GC thread. The size of
// a stripe is a constant, ssize.
//
// +===============+ slice 0
// | stripe 0 |
// +---------------+
// | stripe 1 |
// +---------------+
// | stripe 2 |
// +---------------+
// | stripe 3 |
// +===============+ slice 1
// | stripe 0 |
// +---------------+
// | stripe 1 |
// +---------------+
// | stripe 2 |
// +---------------+
// | stripe 3 |
// +===============+ slice 2
// ...
//
// In this case there are 4 threads, so 4 stripes. A GC thread first works on
// its stripe within slice 0 and then moves to its stripe in the next slice
// until it has exceeded the top of the generation. The distance to stripe in
// the next slice is calculated based on the number of stripes. The next
// stripe is at ssize * number_of_stripes (= slice_stride).. So after
// finishing stripe 0 in slice 0, the thread finds the stripe 0 in slice1 by
// adding slice_stride to the start of stripe 0 in slice 0 to get to the start
// of stride 0 in slice 1.
void PSCardTable::scavenge_contents_parallel(ObjectStartArray* start_array,
MutableSpace* sp,
HeapWord* space_top,
PSPromotionManager* pm,
uint stripe_number,
uint stripe_total) {
int ssize = 128; // Naked constant! Work unit = 64k.
int dirty_card_count = 0;
// It is a waste to get here if empty.
assert(sp->bottom() < sp->top(), "Should not be called if empty");
oop* sp_top = (oop*)space_top;
CardValue* start_card = byte_for(sp->bottom());
CardValue* end_card = byte_for(sp_top - 1) + 1;
oop* last_scanned = NULL; // Prevent scanning objects more than once
// The width of the stripe ssize*stripe_total must be
// consistent with the number of stripes so that the complete slice
// is covered.
size_t slice_width = ssize * stripe_total;
for (CardValue* slice = start_card; slice < end_card; slice += slice_width) {
CardValue* worker_start_card = slice + stripe_number * ssize;
if (worker_start_card >= end_card)
return; // We're done.
CardValue* worker_end_card = worker_start_card + ssize;
if (worker_end_card > end_card)
worker_end_card = end_card;
// We do not want to scan objects more than once. In order to accomplish
// this, we assert that any object with an object head inside our 'slice'
// belongs to us. We may need to extend the range of scanned cards if the
// last object continues into the next 'slice'.
//
// Note! ending cards are exclusive!
HeapWord* slice_start = addr_for(worker_start_card);
HeapWord* slice_end = MIN2((HeapWord*) sp_top, addr_for(worker_end_card));
#ifdef ASSERT
if (GCWorkerDelayMillis > 0) {
// Delay 1 worker so that it proceeds after all the work
// has been completed.
if (stripe_number < 2) {
os::naked_sleep(GCWorkerDelayMillis);
}
}
#endif
// If there are not objects starting within the chunk, skip it.
if (!start_array->object_starts_in_range(slice_start, slice_end)) {
continue;
}
// Update our beginning addr
HeapWord* first_object = start_array->object_start(slice_start);
debug_only(oop* first_object_within_slice = (oop*) first_object;)
if (first_object < slice_start) {
last_scanned = (oop*)(first_object + oop(first_object)->size());
debug_only(first_object_within_slice = last_scanned;)
worker_start_card = byte_for(last_scanned);
}
// Update the ending addr
if (slice_end < (HeapWord*)sp_top) {
// The subtraction is important! An object may start precisely at slice_end.
HeapWord* last_object = start_array->object_start(slice_end - 1);
slice_end = last_object + oop(last_object)->size();
// worker_end_card is exclusive, so bump it one past the end of last_object's
// covered span.
worker_end_card = byte_for(slice_end) + 1;
if (worker_end_card > end_card)
worker_end_card = end_card;
}
assert(slice_end <= (HeapWord*)sp_top, "Last object in slice crosses space boundary");
assert(is_valid_card_address(worker_start_card), "Invalid worker start card");
assert(is_valid_card_address(worker_end_card), "Invalid worker end card");
// Note that worker_start_card >= worker_end_card is legal, and happens when
// an object spans an entire slice.
assert(worker_start_card <= end_card, "worker start card beyond end card");
assert(worker_end_card <= end_card, "worker end card beyond end card");
CardValue* current_card = worker_start_card;
while (current_card < worker_end_card) {
// Find an unclean card.
while (current_card < worker_end_card && card_is_clean(*current_card)) {
current_card++;
}
CardValue* first_unclean_card = current_card;
// Find the end of a run of contiguous unclean cards
while (current_card < worker_end_card && !card_is_clean(*current_card)) {
while (current_card < worker_end_card && !card_is_clean(*current_card)) {
current_card++;
}
if (current_card < worker_end_card) {
// Some objects may be large enough to span several cards. If such
// an object has more than one dirty card, separated by a clean card,
// we will attempt to scan it twice. The test against "last_scanned"
// prevents the redundant object scan, but it does not prevent newly
// marked cards from being cleaned.
HeapWord* last_object_in_dirty_region = start_array->object_start(addr_for(current_card)-1);
size_t size_of_last_object = oop(last_object_in_dirty_region)->size();
HeapWord* end_of_last_object = last_object_in_dirty_region + size_of_last_object;
CardValue* ending_card_of_last_object = byte_for(end_of_last_object);
assert(ending_card_of_last_object <= worker_end_card, "ending_card_of_last_object is greater than worker_end_card");
if (ending_card_of_last_object > current_card) {
// This means the object spans the next complete card.
// We need to bump the current_card to ending_card_of_last_object
current_card = ending_card_of_last_object;
}
}
}
CardValue* following_clean_card = current_card;
if (first_unclean_card < worker_end_card) {
oop* p = (oop*) start_array->object_start(addr_for(first_unclean_card));
assert((HeapWord*)p <= addr_for(first_unclean_card), "checking");
// "p" should always be >= "last_scanned" because newly GC dirtied
// cards are no longer scanned again (see comment at end
// of loop on the increment of "current_card"). Test that
// hypothesis before removing this code.
// If this code is removed, deal with the first time through
// the loop when the last_scanned is the object starting in
// the previous slice.
assert((p >= last_scanned) ||
(last_scanned == first_object_within_slice),
"Should no longer be possible");
if (p < last_scanned) {
// Avoid scanning more than once; this can happen because
// newgen cards set by GC may a different set than the
// originally dirty set
p = last_scanned;
}
oop* to = (oop*)addr_for(following_clean_card);
// Test slice_end first!
if ((HeapWord*)to > slice_end) {
to = (oop*)slice_end;
} else if (to > sp_top) {
to = sp_top;
}
// we know which cards to scan, now clear them
if (first_unclean_card <= worker_start_card+1)
first_unclean_card = worker_start_card+1;
if (following_clean_card >= worker_end_card-1)
following_clean_card = worker_end_card-1;
while (first_unclean_card < following_clean_card) {
*first_unclean_card++ = clean_card;
}
const int interval = PrefetchScanIntervalInBytes;
// scan all objects in the range
if (interval != 0) {
while (p < to) {
Prefetch::write(p, interval);
oop m = oop(p);
assert(oopDesc::is_oop_or_null(m), "Expected an oop or NULL for header field at " PTR_FORMAT, p2i(m));
pm->push_contents(m);
p += m->size();
}
pm->drain_stacks_cond_depth();
} else {
while (p < to) {
oop m = oop(p);
assert(oopDesc::is_oop_or_null(m), "Expected an oop or NULL for header field at " PTR_FORMAT, p2i(m));
pm->push_contents(m);
p += m->size();
}
pm->drain_stacks_cond_depth();
}
last_scanned = p;
}
// "current_card" is still the "following_clean_card" or
// the current_card is >= the worker_end_card so the
// loop will not execute again.
assert((current_card == following_clean_card) ||
(current_card >= worker_end_card),
"current_card should only be incremented if it still equals "
"following_clean_card");
// Increment current_card so that it is not processed again.
// It may now be dirty because a old-to-young pointer was
// found on it an updated. If it is now dirty, it cannot be
// be safely cleaned in the next iteration.
current_card++;
}
}
}
// This should be called before a scavenge.
void PSCardTable::verify_all_young_refs_imprecise() {
CheckForUnmarkedObjects check;
ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
PSOldGen* old_gen = heap->old_gen();
old_gen->object_iterate(&check);
}
// This should be called immediately after a scavenge, before mutators resume.
void PSCardTable::verify_all_young_refs_precise() {
ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
PSOldGen* old_gen = heap->old_gen();
CheckForPreciseMarks check(heap->young_gen(), this);
old_gen->oop_iterate(&check);
verify_all_young_refs_precise_helper(old_gen->object_space()->used_region());
}
void PSCardTable::verify_all_young_refs_precise_helper(MemRegion mr) {
CardValue* bot = byte_for(mr.start());
CardValue* top = byte_for(mr.end());
while (bot <= top) {
assert(*bot == clean_card || *bot == verify_card, "Found unwanted or unknown card mark");
if (*bot == verify_card)
*bot = youngergen_card;
bot++;
}
}
bool PSCardTable::addr_is_marked_imprecise(void *addr) {
CardValue* p = byte_for(addr);
CardValue val = *p;
if (card_is_dirty(val))
return true;
if (card_is_newgen(val))
return true;
if (card_is_clean(val))
return false;
assert(false, "Found unhandled card mark type");
return false;
}
// Also includes verify_card
bool PSCardTable::addr_is_marked_precise(void *addr) {
CardValue* p = byte_for(addr);
CardValue val = *p;
if (card_is_newgen(val))
return true;
if (card_is_verify(val))
return true;
if (card_is_clean(val))
return false;
if (card_is_dirty(val))
return false;
assert(false, "Found unhandled card mark type");
return false;
}
// Assumes that only the base or the end changes. This allows indentification
// of the region that is being resized. The
// CardTable::resize_covered_region() is used for the normal case
// where the covered regions are growing or shrinking at the high end.
// The method resize_covered_region_by_end() is analogous to
// CardTable::resize_covered_region() but
// for regions that grow or shrink at the low end.
void PSCardTable::resize_covered_region(MemRegion new_region) {
for (int i = 0; i < _cur_covered_regions; i++) {
if (_covered[i].start() == new_region.start()) {
// Found a covered region with the same start as the
// new region. The region is growing or shrinking
// from the start of the region.
resize_covered_region_by_start(new_region);
return;
}
if (_covered[i].start() > new_region.start()) {
break;
}
}
int changed_region = -1;
for (int j = 0; j < _cur_covered_regions; j++) {
if (_covered[j].end() == new_region.end()) {
changed_region = j;
// This is a case where the covered region is growing or shrinking
// at the start of the region.
assert(changed_region != -1, "Don't expect to add a covered region");
assert(_covered[changed_region].byte_size() != new_region.byte_size(),
"The sizes should be different here");
resize_covered_region_by_end(changed_region, new_region);
return;
}
}
// This should only be a new covered region (where no existing
// covered region matches at the start or the end).
assert(_cur_covered_regions < _max_covered_regions,
"An existing region should have been found");
resize_covered_region_by_start(new_region);
}
void PSCardTable::resize_covered_region_by_start(MemRegion new_region) {
CardTable::resize_covered_region(new_region);
debug_only(verify_guard();)
}
void PSCardTable::resize_covered_region_by_end(int changed_region,
MemRegion new_region) {
assert(SafepointSynchronize::is_at_safepoint(),
"Only expect an expansion at the low end at a GC");
debug_only(verify_guard();)
#ifdef ASSERT
for (int k = 0; k < _cur_covered_regions; k++) {
if (_covered[k].end() == new_region.end()) {
assert(changed_region == k, "Changed region is incorrect");
break;
}
}
#endif
// Commit new or uncommit old pages, if necessary.
if (resize_commit_uncommit(changed_region, new_region)) {
// Set the new start of the committed region
resize_update_committed_table(changed_region, new_region);
}
// Update card table entries
resize_update_card_table_entries(changed_region, new_region);
// Update the covered region
resize_update_covered_table(changed_region, new_region);
int ind = changed_region;
log_trace(gc, barrier)("CardTable::resize_covered_region: ");
log_trace(gc, barrier)(" _covered[%d].start(): " INTPTR_FORMAT " _covered[%d].last(): " INTPTR_FORMAT,
ind, p2i(_covered[ind].start()), ind, p2i(_covered[ind].last()));
log_trace(gc, barrier)(" _committed[%d].start(): " INTPTR_FORMAT " _committed[%d].last(): " INTPTR_FORMAT,
ind, p2i(_committed[ind].start()), ind, p2i(_committed[ind].last()));
log_trace(gc, barrier)(" byte_for(start): " INTPTR_FORMAT " byte_for(last): " INTPTR_FORMAT,
p2i(byte_for(_covered[ind].start())), p2i(byte_for(_covered[ind].last())));
log_trace(gc, barrier)(" addr_for(start): " INTPTR_FORMAT " addr_for(last): " INTPTR_FORMAT,
p2i(addr_for((CardValue*) _committed[ind].start())), p2i(addr_for((CardValue*) _committed[ind].last())));
debug_only(verify_guard();)
}
bool PSCardTable::resize_commit_uncommit(int changed_region,
MemRegion new_region) {
bool result = false;
// Commit new or uncommit old pages, if necessary.
MemRegion cur_committed = _committed[changed_region];
assert(_covered[changed_region].end() == new_region.end(),
"The ends of the regions are expected to match");
// Extend the start of this _committed region to
// to cover the start of any previous _committed region.
// This forms overlapping regions, but never interior regions.
HeapWord* min_prev_start = lowest_prev_committed_start(changed_region);
if (min_prev_start < cur_committed.start()) {
// Only really need to set start of "cur_committed" to
// the new start (min_prev_start) but assertion checking code
// below use cur_committed.end() so make it correct.
MemRegion new_committed =
MemRegion(min_prev_start, cur_committed.end());
cur_committed = new_committed;
}
#ifdef ASSERT
ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();
assert(cur_committed.start() == align_up(cur_committed.start(), os::vm_page_size()),
"Starts should have proper alignment");
#endif
CardValue* new_start = byte_for(new_region.start());
// Round down because this is for the start address
HeapWord* new_start_aligned = align_down((HeapWord*)new_start, os::vm_page_size());
// The guard page is always committed and should not be committed over.
// This method is used in cases where the generation is growing toward
// lower addresses but the guard region is still at the end of the
// card table. That still makes sense when looking for writes
// off the end of the card table.
if (new_start_aligned < cur_committed.start()) {
// Expand the committed region
//
// Case A
// |+ guard +|
// |+ cur committed +++++++++|
// |+ new committed +++++++++++++++++|
//
// Case B
// |+ guard +|
// |+ cur committed +|
// |+ new committed +++++++|
//
// These are not expected because the calculation of the
// cur committed region and the new committed region
// share the same end for the covered region.
// Case C
// |+ guard +|
// |+ cur committed +|
// |+ new committed +++++++++++++++++|
// Case D
// |+ guard +|
// |+ cur committed +++++++++++|
// |+ new committed +++++++|
HeapWord* new_end_for_commit =
MIN2(cur_committed.end(), _guard_region.start());
if(new_start_aligned < new_end_for_commit) {
MemRegion new_committed =
MemRegion(new_start_aligned, new_end_for_commit);
os::commit_memory_or_exit((char*)new_committed.start(),
new_committed.byte_size(), !ExecMem,
"card table expansion");
}
result = true;
} else if (new_start_aligned > cur_committed.start()) {
// Shrink the committed region
#if 0 // uncommitting space is currently unsafe because of the interactions
// of growing and shrinking regions. One region A can uncommit space
// that it owns but which is being used by another region B (maybe).
// Region B has not committed the space because it was already
// committed by region A.
MemRegion uncommit_region = committed_unique_to_self(changed_region,
MemRegion(cur_committed.start(), new_start_aligned));
if (!uncommit_region.is_empty()) {
if (!os::uncommit_memory((char*)uncommit_region.start(),
uncommit_region.byte_size())) {
// If the uncommit fails, ignore it. Let the
// committed table resizing go even though the committed
// table will over state the committed space.
}
}
#else
assert(!result, "Should be false with current workaround");
#endif
}
assert(_committed[changed_region].end() == cur_committed.end(),
"end should not change");
return result;
}
void PSCardTable::resize_update_committed_table(int changed_region,
MemRegion new_region) {
CardValue* new_start = byte_for(new_region.start());
// Set the new start of the committed region
HeapWord* new_start_aligned = align_down((HeapWord*)new_start, os::vm_page_size());
MemRegion new_committed = MemRegion(new_start_aligned,
_committed[changed_region].end());
_committed[changed_region] = new_committed;
_committed[changed_region].set_start(new_start_aligned);
}
void PSCardTable::resize_update_card_table_entries(int changed_region,
MemRegion new_region) {
debug_only(verify_guard();)
MemRegion original_covered = _covered[changed_region];
// Initialize the card entries. Only consider the
// region covered by the card table (_whole_heap)
CardValue* entry;
if (new_region.start() < _whole_heap.start()) {
entry = byte_for(_whole_heap.start());
} else {
entry = byte_for(new_region.start());
}
CardValue* end = byte_for(original_covered.start());
// If _whole_heap starts at the original covered regions start,
// this loop will not execute.
while (entry < end) { *entry++ = clean_card; }
}
void PSCardTable::resize_update_covered_table(int changed_region,
MemRegion new_region) {
// Update the covered region
_covered[changed_region].set_start(new_region.start());
_covered[changed_region].set_word_size(new_region.word_size());
// reorder regions. There should only be at most 1 out
// of order.
for (int i = _cur_covered_regions-1 ; i > 0; i--) {
if (_covered[i].start() < _covered[i-1].start()) {
MemRegion covered_mr = _covered[i-1];
_covered[i-1] = _covered[i];
_covered[i] = covered_mr;
MemRegion committed_mr = _committed[i-1];
_committed[i-1] = _committed[i];
_committed[i] = committed_mr;
break;
}
}
#ifdef ASSERT
for (int m = 0; m < _cur_covered_regions-1; m++) {
assert(_covered[m].start() <= _covered[m+1].start(),
"Covered regions out of order");
assert(_committed[m].start() <= _committed[m+1].start(),
"Committed regions out of order");
}
#endif
}
// Returns the start of any committed region that is lower than
// the target committed region (index ind) and that intersects the
// target region. If none, return start of target region.
//
// -------------
// | |
// -------------
// ------------
// | target |
// ------------
// -------------
// | |
// -------------
// ^ returns this
//
// -------------
// | |
// -------------
// ------------
// | target |
// ------------
// -------------
// | |
// -------------
// ^ returns this
HeapWord* PSCardTable::lowest_prev_committed_start(int ind) const {
assert(_cur_covered_regions >= 0, "Expecting at least on region");
HeapWord* min_start = _committed[ind].start();
for (int j = 0; j < ind; j++) {
HeapWord* this_start = _committed[j].start();
if ((this_start < min_start) &&
!(_committed[j].intersection(_committed[ind])).is_empty()) {
min_start = this_start;
}
}
return min_start;
}
bool PSCardTable::is_in_young(oop obj) const {
return ParallelScavengeHeap::heap()->is_in_young(obj);
}