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8214259: Implementation: JEP 189: Shenandoah: A Low-Pause-Time Garbage Collector (Experimental)

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Co-authored-by: Christine Flood <chf@redhat.com>
Co-authored-by: Aleksey Shipilev <shade@redhat.com>
Co-authored-by: Roland Westrelin <rwestrel@redhat.com>
Co-authored-by: Zhenygu Gu <zgu@redhat.com>
Co-authored-by: Andrew Haley <aph@redhat.com>
Co-authored-by: Andrew Dinn <adinn@redhat.com>
Co-authored-by: Mario Torre <mtorre@redhat.com>
Reviewed-by: kvn, roland, shade, coleenp, lmesnik, pliden, jgeorge, ihse, erikj
This commit is contained in:
Roman Kennke 2018-12-10 15:47:44 +01:00
parent 0639a6303b
commit 8b62a2ee9d
297 changed files with 40569 additions and 325 deletions
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src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp Normal file
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/*
* Copyright (c) 2013, 2018, Red Hat, Inc. All rights reserved.
*
* 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/shenandoah/shenandoahConcurrentMark.inline.hpp"
#include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
#include "gc/shenandoah/shenandoahFreeSet.hpp"
#include "gc/shenandoah/shenandoahPhaseTimings.hpp"
#include "gc/shenandoah/shenandoahHeap.inline.hpp"
#include "gc/shenandoah/shenandoahHeuristics.hpp"
#include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
#include "gc/shenandoah/shenandoahControlThread.hpp"
#include "gc/shenandoah/shenandoahTraversalGC.hpp"
#include "gc/shenandoah/shenandoahUtils.hpp"
#include "gc/shenandoah/shenandoahVMOperations.hpp"
#include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
#include "memory/iterator.hpp"
#include "memory/universe.hpp"
ShenandoahControlThread::ShenandoahControlThread() :
ConcurrentGCThread(),
_alloc_failure_waiters_lock(Mutex::leaf, "ShenandoahAllocFailureGC_lock", true, Monitor::_safepoint_check_always),
_gc_waiters_lock(Mutex::leaf, "ShenandoahRequestedGC_lock", true, Monitor::_safepoint_check_always),
_periodic_task(this),
_requested_gc_cause(GCCause::_no_cause_specified),
_degen_point(ShenandoahHeap::_degenerated_outside_cycle),
_allocs_seen(0) {
create_and_start();
_periodic_task.enroll();
_periodic_satb_flush_task.enroll();
}
ShenandoahControlThread::~ShenandoahControlThread() {
// This is here so that super is called.
}
void ShenandoahPeriodicTask::task() {
_thread->handle_force_counters_update();
_thread->handle_counters_update();
}
void ShenandoahPeriodicSATBFlushTask::task() {
ShenandoahHeap::heap()->force_satb_flush_all_threads();
}
void ShenandoahControlThread::run_service() {
ShenandoahHeap* heap = ShenandoahHeap::heap();
int sleep = ShenandoahControlIntervalMin;
double last_shrink_time = os::elapsedTime();
double last_sleep_adjust_time = os::elapsedTime();
// Shrink period avoids constantly polling regions for shrinking.
// Having a period 10x lower than the delay would mean we hit the
// shrinking with lag of less than 1/10-th of true delay.
// ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
ShenandoahHeuristics* heuristics = heap->heuristics();
while (!in_graceful_shutdown() && !should_terminate()) {
// Figure out if we have pending requests.
bool alloc_failure_pending = _alloc_failure_gc.is_set();
bool explicit_gc_requested = _gc_requested.is_set() && is_explicit_gc(_requested_gc_cause);
bool implicit_gc_requested = _gc_requested.is_set() && !is_explicit_gc(_requested_gc_cause);
// This control loop iteration have seen this much allocations.
size_t allocs_seen = Atomic::xchg<size_t>(0, &_allocs_seen);
// Choose which GC mode to run in. The block below should select a single mode.
GCMode mode = none;
GCCause::Cause cause = GCCause::_last_gc_cause;
ShenandoahHeap::ShenandoahDegenPoint degen_point = ShenandoahHeap::_degenerated_unset;
if (alloc_failure_pending) {
// Allocation failure takes precedence: we have to deal with it first thing
log_info(gc)("Trigger: Handle Allocation Failure");
cause = GCCause::_allocation_failure;
// Consume the degen point, and seed it with default value
degen_point = _degen_point;
_degen_point = ShenandoahHeap::_degenerated_outside_cycle;
if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
heuristics->record_allocation_failure_gc();
policy->record_alloc_failure_to_degenerated(degen_point);
mode = stw_degenerated;
} else {
heuristics->record_allocation_failure_gc();
policy->record_alloc_failure_to_full();
mode = stw_full;
}
} else if (explicit_gc_requested) {
cause = _requested_gc_cause;
log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
heuristics->record_requested_gc();
if (ExplicitGCInvokesConcurrent) {
policy->record_explicit_to_concurrent();
if (heuristics->can_do_traversal_gc()) {
mode = concurrent_traversal;
} else {
mode = concurrent_normal;
}
// Unload and clean up everything
heap->set_process_references(heuristics->can_process_references());
heap->set_unload_classes(heuristics->can_unload_classes());
} else {
policy->record_explicit_to_full();
mode = stw_full;
}
} else if (implicit_gc_requested) {
cause = _requested_gc_cause;
log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
heuristics->record_requested_gc();
if (ShenandoahImplicitGCInvokesConcurrent) {
policy->record_implicit_to_concurrent();
if (heuristics->can_do_traversal_gc()) {
mode = concurrent_traversal;
} else {
mode = concurrent_normal;
}
// Unload and clean up everything
heap->set_process_references(heuristics->can_process_references());
heap->set_unload_classes(heuristics->can_unload_classes());
} else {
policy->record_implicit_to_full();
mode = stw_full;
}
} else {
// Potential normal cycle: ask heuristics if it wants to act
if (heuristics->should_start_traversal_gc()) {
mode = concurrent_traversal;
cause = GCCause::_shenandoah_traversal_gc;
} else if (heuristics->should_start_normal_gc()) {
mode = concurrent_normal;
cause = GCCause::_shenandoah_concurrent_gc;
}
// Ask policy if this cycle wants to process references or unload classes
heap->set_process_references(heuristics->should_process_references());
heap->set_unload_classes(heuristics->should_unload_classes());
}
// Blow all soft references on this cycle, if handling allocation failure,
// or we are requested to do so unconditionally.
if (alloc_failure_pending || ShenandoahAlwaysClearSoftRefs) {
heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
}
bool gc_requested = (mode != none);
assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
if (gc_requested) {
heap->reset_bytes_allocated_since_gc_start();
// If GC was requested, we are sampling the counters even without actual triggers
// from allocation machinery. This captures GC phases more accurately.
set_forced_counters_update(true);
// If GC was requested, we better dump freeset data for performance debugging
{
ShenandoahHeapLocker locker(heap->lock());
heap->free_set()->log_status();
}
}
switch (mode) {
case none:
break;
case concurrent_traversal:
service_concurrent_traversal_cycle(cause);
break;
case concurrent_normal:
service_concurrent_normal_cycle(cause);
break;
case stw_degenerated:
service_stw_degenerated_cycle(cause, degen_point);
break;
case stw_full:
service_stw_full_cycle(cause);
break;
default:
ShouldNotReachHere();
}
if (gc_requested) {
// If this was the requested GC cycle, notify waiters about it
if (explicit_gc_requested || implicit_gc_requested) {
notify_gc_waiters();
}
// If this was the allocation failure GC cycle, notify waiters about it
if (alloc_failure_pending) {
notify_alloc_failure_waiters();
}
// Report current free set state at the end of cycle, whether
// it is a normal completion, or the abort.
{
ShenandoahHeapLocker locker(heap->lock());
heap->free_set()->log_status();
// Notify Universe about new heap usage. This has implications for
// global soft refs policy, and we better report it every time heap
// usage goes down.
Universe::update_heap_info_at_gc();
}
// Disable forced counters update, and update counters one more time
// to capture the state at the end of GC session.
handle_force_counters_update();
set_forced_counters_update(false);
// Retract forceful part of soft refs policy
heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
// Clear metaspace oom flag, if current cycle unloaded classes
if (heap->unload_classes()) {
heuristics->clear_metaspace_oom();
}
// GC is over, we are at idle now
if (ShenandoahPacing) {
heap->pacer()->setup_for_idle();
}
} else {
// Allow allocators to know we have seen this much regions
if (ShenandoahPacing && (allocs_seen > 0)) {
heap->pacer()->report_alloc(allocs_seen);
}
}
double current = os::elapsedTime();
if (ShenandoahUncommit && (explicit_gc_requested || (current - last_shrink_time > shrink_period))) {
// Try to uncommit enough stale regions. Explicit GC tries to uncommit everything.
// Regular paths uncommit only occasionally.
double shrink_before = explicit_gc_requested ?
current :
current - (ShenandoahUncommitDelay / 1000.0);
service_uncommit(shrink_before);
last_shrink_time = current;
}
// Wait before performing the next action. If allocation happened during this wait,
// we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
// back off exponentially.
if (_heap_changed.try_unset()) {
sleep = ShenandoahControlIntervalMin;
} else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
last_sleep_adjust_time = current;
}
os::naked_short_sleep(sleep);
}
// Wait for the actual stop(), can't leave run_service() earlier.
while (!should_terminate()) {
os::naked_short_sleep(ShenandoahControlIntervalMin);
}
}
void ShenandoahControlThread::service_concurrent_traversal_cycle(GCCause::Cause cause) {
GCIdMark gc_id_mark;
ShenandoahGCSession session(cause);
ShenandoahHeap* heap = ShenandoahHeap::heap();
TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
// Reset for upcoming cycle
heap->entry_reset();
heap->vmop_entry_init_traversal();
if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_traversal)) return;
heap->entry_traversal();
if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_traversal)) return;
heap->vmop_entry_final_traversal();
heap->entry_cleanup();
heap->heuristics()->record_success_concurrent();
heap->shenandoah_policy()->record_success_concurrent();
}
void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
// Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
// any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
// If second allocation failure happens during Degenerated GC cycle (for example, when GC
// tries to evac something and no memory is available), cycle degrades to Full GC.
//
// There are also two shortcuts through the normal cycle: a) immediate garbage shortcut, when
// heuristics says there are no regions to compact, and all the collection comes from immediately
// reclaimable regions; b) coalesced UR shortcut, when heuristics decides to coalesce UR with the
// mark from the next cycle.
//
// ................................................................................................
//
// (immediate garbage shortcut) Concurrent GC
// /-------------------------------------------\
// | (coalesced UR) v
// | /----------------------->o
// | | |
// | | v
// [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
// | | | ^
// | (af) | (af) | (af) |
// ..................|....................|.................|..............|.......................
// | | | |
// | | | | Degenerated GC
// v v v |
// STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
// | | | ^
// | (af) | (af) | (af) |
// ..................|....................|.................|..............|.......................
// | | | |
// | v | | Full GC
// \------------------->o<----------------/ |
// | |
// v |
// Full GC --------------------------/
//
ShenandoahHeap* heap = ShenandoahHeap::heap();
if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_outside_cycle)) return;
GCIdMark gc_id_mark;
ShenandoahGCSession session(cause);
TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
// Reset for upcoming marking
heap->entry_reset();
// Start initial mark under STW
heap->vmop_entry_init_mark();
// Continue concurrent mark
heap->entry_mark();
if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_mark)) return;
// If not cancelled, can try to concurrently pre-clean
heap->entry_preclean();
// Complete marking under STW, and start evacuation
heap->vmop_entry_final_mark();
// Continue the cycle with evacuation and optional update-refs.
// This may be skipped if there is nothing to evacuate.
// If so, evac_in_progress would be unset by collection set preparation code.
if (heap->is_evacuation_in_progress()) {
// Final mark had reclaimed some immediate garbage, kick cleanup to reclaim the space
// for the rest of the cycle, and report current state of free set.
heap->entry_cleanup();
{
ShenandoahHeapLocker locker(heap->lock());
heap->free_set()->log_status();
}
// Concurrently evacuate
heap->entry_evac();
if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_evac)) return;
// Perform update-refs phase, if required. This phase can be skipped if heuristics
// decides to piggy-back the update-refs on the next marking cycle. On either path,
// we need to turn off evacuation: either in init-update-refs, or in final-evac.
if (heap->heuristics()->should_start_update_refs()) {
heap->vmop_entry_init_updaterefs();
heap->entry_updaterefs();
if (check_cancellation_or_degen(ShenandoahHeap::_degenerated_updaterefs)) return;
heap->vmop_entry_final_updaterefs();
} else {
heap->vmop_entry_final_evac();
}
}
// Reclaim space after cycle
heap->entry_cleanup();
// Cycle is complete
heap->heuristics()->record_success_concurrent();
heap->shenandoah_policy()->record_success_concurrent();
}
bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahHeap::ShenandoahDegenPoint point) {
ShenandoahHeap* heap = ShenandoahHeap::heap();
if (heap->cancelled_gc()) {
assert (is_alloc_failure_gc() || in_graceful_shutdown(), "Cancel GC either for alloc failure GC, or gracefully exiting");
if (!in_graceful_shutdown()) {
assert (_degen_point == ShenandoahHeap::_degenerated_outside_cycle,
"Should not be set yet: %s", ShenandoahHeap::degen_point_to_string(_degen_point));
_degen_point = point;
}
return true;
}
return false;
}
void ShenandoahControlThread::stop_service() {
// Nothing to do here.
}
void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
GCIdMark gc_id_mark;
ShenandoahGCSession session(cause);
ShenandoahHeap* heap = ShenandoahHeap::heap();
heap->vmop_entry_full(cause);
heap->heuristics()->record_success_full();
heap->shenandoah_policy()->record_success_full();
}
void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahHeap::ShenandoahDegenPoint point) {
assert (point != ShenandoahHeap::_degenerated_unset, "Degenerated point should be set");
GCIdMark gc_id_mark;
ShenandoahGCSession session(cause);
ShenandoahHeap* heap = ShenandoahHeap::heap();
heap->vmop_degenerated(point);
heap->heuristics()->record_success_degenerated();
heap->shenandoah_policy()->record_success_degenerated();
}
void ShenandoahControlThread::service_uncommit(double shrink_before) {
ShenandoahHeap* heap = ShenandoahHeap::heap();
// Scan through the heap and determine if there is work to do. This avoids taking
// heap lock if there is no work available, avoids spamming logs with superfluous
// logging messages, and minimises the amount of work while locks are taken.
bool has_work = false;
for (size_t i = 0; i < heap->num_regions(); i++) {
ShenandoahHeapRegion *r = heap->get_region(i);
if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
has_work = true;
break;
}
}
if (has_work) {
heap->entry_uncommit(shrink_before);
}
}
bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
return GCCause::is_user_requested_gc(cause) ||
GCCause::is_serviceability_requested_gc(cause);
}
void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
assert(GCCause::is_user_requested_gc(cause) ||
GCCause::is_serviceability_requested_gc(cause) ||
cause == GCCause::_metadata_GC_clear_soft_refs ||
cause == GCCause::_full_gc_alot ||
cause == GCCause::_wb_full_gc ||
cause == GCCause::_scavenge_alot,
"only requested GCs here");
if (is_explicit_gc(cause)) {
if (!DisableExplicitGC) {
handle_requested_gc(cause);
}
} else {
handle_requested_gc(cause);
}
}
void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
_requested_gc_cause = cause;
_gc_requested.set();
MonitorLockerEx ml(&_gc_waiters_lock);
while (_gc_requested.is_set()) {
ml.wait();
}
}
void ShenandoahControlThread::handle_alloc_failure(size_t words) {
ShenandoahHeap* heap = ShenandoahHeap::heap();
assert(current()->is_Java_thread(), "expect Java thread here");
if (try_set_alloc_failure_gc()) {
// Only report the first allocation failure
log_info(gc)("Failed to allocate " SIZE_FORMAT "%s",
byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
// Now that alloc failure GC is scheduled, we can abort everything else
heap->cancel_gc(GCCause::_allocation_failure);
}
MonitorLockerEx ml(&_alloc_failure_waiters_lock);
while (is_alloc_failure_gc()) {
ml.wait();
}
}
void ShenandoahControlThread::handle_alloc_failure_evac(size_t words) {
ShenandoahHeap* heap = ShenandoahHeap::heap();
if (try_set_alloc_failure_gc()) {
// Only report the first allocation failure
log_info(gc)("Failed to allocate " SIZE_FORMAT "%s for evacuation",
byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
}
// Forcefully report allocation failure
heap->cancel_gc(GCCause::_shenandoah_allocation_failure_evac);
}
void ShenandoahControlThread::notify_alloc_failure_waiters() {
_alloc_failure_gc.unset();
MonitorLockerEx ml(&_alloc_failure_waiters_lock);
ml.notify_all();
}
bool ShenandoahControlThread::try_set_alloc_failure_gc() {
return _alloc_failure_gc.try_set();
}
bool ShenandoahControlThread::is_alloc_failure_gc() {
return _alloc_failure_gc.is_set();
}
void ShenandoahControlThread::notify_gc_waiters() {
_gc_requested.unset();
MonitorLockerEx ml(&_gc_waiters_lock);
ml.notify_all();
}
void ShenandoahControlThread::handle_counters_update() {
if (_do_counters_update.is_set()) {
_do_counters_update.unset();
ShenandoahHeap::heap()->monitoring_support()->update_counters();
}
}
void ShenandoahControlThread::handle_force_counters_update() {
if (_force_counters_update.is_set()) {
_do_counters_update.unset(); // reset these too, we do update now!
ShenandoahHeap::heap()->monitoring_support()->update_counters();
}
}
void ShenandoahControlThread::notify_heap_changed() {
// This is called from allocation path, and thus should be fast.
// Update monitoring counters when we took a new region. This amortizes the
// update costs on slow path.
if (_do_counters_update.is_unset()) {
_do_counters_update.set();
}
// Notify that something had changed.
if (_heap_changed.is_unset()) {
_heap_changed.set();
}
}
void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
assert(ShenandoahPacing, "should only call when pacing is enabled");
Atomic::add(words, &_allocs_seen);
}
void ShenandoahControlThread::set_forced_counters_update(bool value) {
_force_counters_update.set_cond(value);
}
void ShenandoahControlThread::print() const {
print_on(tty);
}
void ShenandoahControlThread::print_on(outputStream* st) const {
st->print("Shenandoah Concurrent Thread");
Thread::print_on(st);
st->cr();
}
void ShenandoahControlThread::start() {
create_and_start();
}
void ShenandoahControlThread::prepare_for_graceful_shutdown() {
_graceful_shutdown.set();
}
bool ShenandoahControlThread::in_graceful_shutdown() {
return _graceful_shutdown.is_set();
}