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Add JFR GCTLABConfiguration Event #24307

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3 changes: 3 additions & 0 deletions runtime/gc/gctable.c
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Original file line number Diff line number Diff line change
Expand Up @@ -118,6 +118,9 @@ J9MemoryManagerFunctions MemoryManagerFunctions = {
j9gc_get_softmx,
j9gc_get_initial_heap_size,
j9gc_get_maximum_heap_size,
j9gc_get_tlh_minimum_size,
j9gc_get_tlh_initial_size,
j9gc_is_tlab_enabled,
j9gc_get_minimum_young_generation_size,
j9gc_get_maximum_young_generation_size,
j9gc_objaccess_checkClassLive,
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3 changes: 3 additions & 0 deletions runtime/gc_base/gc_internal.h
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Expand Up @@ -139,6 +139,9 @@ extern J9_CFUNC jint JNICALL queryGCStatus(JavaVM *vm, jint *nHeaps, GCStatus *
extern J9_CFUNC int j9gc_finalizer_startup(J9JavaVM * vm);
extern J9_CFUNC UDATA j9gc_wait_for_reference_processing(J9JavaVM *vm);
extern J9_CFUNC UDATA j9gc_get_maximum_heap_size(J9JavaVM *javaVM);
extern J9_CFUNC UDATA j9gc_get_tlh_minimum_size(J9JavaVM *javaVM);
extern J9_CFUNC UDATA j9gc_get_tlh_initial_size(J9JavaVM *javaVM);
extern J9_CFUNC BOOLEAN j9gc_is_tlab_enabled(J9JavaVM *javaVM);
extern J9_CFUNC void* j9gc_get_heap_base(J9JavaVM *javaVM);
extern J9_CFUNC void* j9gc_get_heap_top(J9JavaVM *javaVM);
extern J9_CFUNC UDATA j9gc_get_minimum_young_generation_size(J9JavaVM *javaVM);
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29 changes: 29 additions & 0 deletions runtime/gc_base/modronapi.cpp
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Expand Up @@ -856,6 +856,35 @@ j9gc_get_maximum_heap_size(J9JavaVM *javaVM)
return size;
}

/**
* API to return the minimum TLH (Thread Local Heap) size.
*/
UDATA
j9gc_get_tlh_minimum_size(J9JavaVM *javaVM)
{
return MM_GCExtensions::getExtensions(javaVM)->tlhMinimumSize;
}

/**
* API to return the initial TLH (Thread Local Heap) size.
*/
UDATA
j9gc_get_tlh_initial_size(J9JavaVM *javaVM)
{
return MM_GCExtensions::getExtensions(javaVM)->tlhInitialSize;
}

/**
* API to return whether TLH allocation is enabled.
*/
BOOLEAN
j9gc_is_tlab_enabled(J9JavaVM *javaVM)
{
uintptr_t allocType = 0;
UDATA found = javaVM->memoryManagerFunctions->j9gc_modron_getConfigurationValueForKey(javaVM, j9gc_modron_configuration_allocationType, &allocType);
return (found && (j9gc_modron_allocation_type_tlh == allocType)) ? TRUE : FALSE;
}

/**
* API to return the heap base address
*/
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3 changes: 3 additions & 0 deletions runtime/gc_base/modronapi.hpp
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Expand Up @@ -85,6 +85,9 @@ UDATA j9gc_set_softmx(J9JavaVM *javaVM, UDATA newsoftMx);
UDATA j9gc_get_softmx(J9JavaVM *javaVM);
UDATA j9gc_get_initial_heap_size(J9JavaVM *javaVM);
UDATA j9gc_get_maximum_heap_size(J9JavaVM *javaVM);
UDATA j9gc_get_tlh_minimum_size(J9JavaVM *javaVM);
UDATA j9gc_get_tlh_initial_size(J9JavaVM *javaVM);
BOOLEAN j9gc_is_tlab_enabled(J9JavaVM *javaVM);
void *j9gc_get_heap_base(J9JavaVM *javaVM);
void *j9gc_get_heap_top(J9JavaVM *javaVM);
UDATA j9gc_get_minimum_young_generation_size(J9JavaVM *javaVM);
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1 change: 1 addition & 0 deletions runtime/oti/j9consts.h
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Expand Up @@ -1012,6 +1012,7 @@ extern "C" {
#define J9JFR_EVENT_TYPE_NATIVE_LIBRARY 32
#define J9JFR_EVENT_TYPE_THREAD_DUMP 33
#define J9JFR_EVENT_TYPE_THREAD_ALLOCATION_STATISTICS 34
#define J9JFR_EVENT_TYPE_GC_TLAB_CONFIGURATION 36

/* JFR thread states. */

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10 changes: 10 additions & 0 deletions runtime/oti/j9nonbuilder.h
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Expand Up @@ -590,6 +590,13 @@ typedef struct J9JFRThreadAllocationStatistics {
U_64 allocated;
} J9JFRThreadAllocationStatistics;

typedef struct J9JFRGCTLABConfiguration {
J9JFR_EVENT_COMMON_FIELDS
BOOLEAN usesTLABs;
U_64 minTLABSize;
U_64 tlabRefillWasteLimit;
} J9JFRGCTLABConfiguration;

#endif /* defined(J9VM_OPT_JFR) */

/* @ddr_namespace: map_to_type=J9CfrError */
Expand Down Expand Up @@ -5044,6 +5051,9 @@ typedef struct J9MemoryManagerFunctions {
UDATA ( *j9gc_get_softmx)(struct J9JavaVM *javaVM) ;
UDATA ( *j9gc_get_initial_heap_size)(struct J9JavaVM *javaVM) ;
UDATA ( *j9gc_get_maximum_heap_size)(struct J9JavaVM *javaVM) ;
UDATA ( *j9gc_get_tlh_minimum_size)(struct J9JavaVM *javaVM) ;
UDATA ( *j9gc_get_tlh_initial_size)(struct J9JavaVM *javaVM) ;
BOOLEAN ( *j9gc_is_tlab_enabled)(struct J9JavaVM *javaVM) ;
UDATA ( *j9gc_get_minimum_young_generation_size)(struct J9JavaVM *javaVM) ;
UDATA ( *j9gc_get_maximum_young_generation_size)(struct J9JavaVM *javaVM) ;
UDATA ( *j9gc_objaccess_checkClassLive)(struct J9JavaVM *javaVM, J9Class *classPtr) ;
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27 changes: 27 additions & 0 deletions runtime/vm/JFRChunkWriter.cpp
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Expand Up @@ -1004,6 +1004,33 @@ VM_JFRChunkWriter::writeYoungGenerationConfigurationEvent()
writeEventSize(dataStart);
}

void
VM_JFRChunkWriter::writeGCTLABConfigurationEvent()
{
GCTLABConfigurationEntry *tlabConfig = &(VM_JFRConstantPoolTypes::getJFRConstantEvents(_vm)->GCTLABConfigEntry);

/* reserve size field */
U_8 *dataStart = reserveEventSize();

/* write event type */
_bufferWriter->writeLEB128(GCTLABConfigurationID);

/* write event start time */
_bufferWriter->writeLEB128(j9time_nano_time());

/* write whether TLABs are in use */
_bufferWriter->writeBoolean(tlabConfig->usesTLABs);

/* write minimum TLAB size */
_bufferWriter->writeLEB128(tlabConfig->minTLABSize);

/* write TLAB refill waste limit */
_bufferWriter->writeLEB128(tlabConfig->tlabRefillWasteLimit);

/* write event size */
writeEventSize(dataStart);
}

void
VM_JFRChunkWriter::writeInitialSystemPropertyEvents(J9JavaVM *vm)
{
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9 changes: 9 additions & 0 deletions runtime/vm/JFRChunkWriter.hpp
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Expand Up @@ -122,6 +122,7 @@ enum MetadataTypeID {
NativeLibraryID = 112,
ModuleRequireID = 113,
ModuleExportID = 114,
GCTLABConfigurationID = 132,
GCHeapConfigID = 133,
YoungGenerationConfigID = 134,
VirtualSpaceID = 149,
Expand Down Expand Up @@ -509,6 +510,8 @@ class VM_JFRChunkWriter {
writeGCHeapConfigurationEvent();

writeYoungGenerationConfigurationEvent();

writeGCTLABConfigurationEvent();
}

writePhysicalMemoryEvent();
Expand Down Expand Up @@ -545,6 +548,10 @@ class VM_JFRChunkWriter {
writeYoungGenerationConfigurationEvent();
}

if (_constantPoolTypes.shouldWriteGCTLABConfigurationEvent()) {
writeGCTLABConfigurationEvent();
}

if (_constantPoolTypes.shouldWritePhysicalMemory()) {
writePhysicalMemoryEvent();
}
Expand Down Expand Up @@ -953,6 +960,8 @@ class VM_JFRChunkWriter {

void writeYoungGenerationConfigurationEvent();

void writeGCTLABConfigurationEvent();

void writeInitialSystemPropertyEvents(J9JavaVM *vm);

void writeInitialEnvironmentVariableEvents();
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38 changes: 38 additions & 0 deletions runtime/vm/JFRConstantPoolTypes.hpp
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Expand Up @@ -439,6 +439,12 @@ struct YoungGenerationConfigurationEntry {
U_64 newRatio;
};

struct GCTLABConfigurationEntry {
BOOLEAN usesTLABs;
U_64 minTLABSize;
U_64 tlabRefillWasteLimit;
};

struct VirtualizationInformationEntry {
const char *name;
};
Expand Down Expand Up @@ -474,6 +480,7 @@ struct JFRConstantEvents {
OSInformationEntry OSInfoEntry;
GCHeapConfigurationEntry GCHeapConfigEntry;
YoungGenerationConfigurationEntry YoungGenConfigEntry;
GCTLABConfigurationEntry GCTLABConfigEntry;
};

class VM_JFRConstantPoolTypes {
Expand Down Expand Up @@ -579,6 +586,7 @@ class VM_JFRConstantPoolTypes {
bool _shouldWriteModuleRequire;
bool _shouldWriteModuleExport;
bool _shouldWriteClassLoaderStatistics;
bool _shouldWriteGCTLABConfigurationEvent;

/* Processing buffers */
StackFrame *_currentStackFrameBuffer;
Expand Down Expand Up @@ -1314,6 +1322,11 @@ class VM_JFRConstantPoolTypes {
return _shouldWriteYoungGenerationConfigurationEvent;
}

bool shouldWriteGCTLABConfigurationEvent()
{
return _shouldWriteGCTLABConfigurationEvent;
}

bool shouldWritePhysicalMemory()
{
return _shouldWritePhysicalMemory;
Expand Down Expand Up @@ -1474,6 +1487,9 @@ class VM_JFRConstantPoolTypes {
case J9JFR_EVENT_TYPE_THREAD_ALLOCATION_STATISTICS:
addThreadAllocationStatistics((J9JFRThreadAllocationStatistics *)event);
break;
case J9JFR_EVENT_TYPE_GC_TLAB_CONFIGURATION:
_shouldWriteGCTLABConfigurationEvent = true;
break;
default:
Assert_VM_unreachable();
break;
Expand Down Expand Up @@ -1569,6 +1585,7 @@ class VM_JFRConstantPoolTypes {
initializeOSInformation(vm, result);
initializeGCHeapConfigurationEvent(vm);
initializeYoungGenerationConfigurationEvent(vm);
initializeGCTLABConfigurationEvent(vm);
}

/**
Expand Down Expand Up @@ -1828,6 +1845,26 @@ class VM_JFRConstantPoolTypes {
}
}

/**
* Initialize GCTLABConfigurationEntry
*
* @param vm[in] the J9JavaVM
*/
static void initializeGCTLABConfigurationEvent(J9JavaVM *vm)
{
J9MemoryManagerFunctions *mmFuncs = vm->memoryManagerFunctions;
GCTLABConfigurationEntry *tlabConfiguration = &(getJFRConstantEvents(vm)->GCTLABConfigEntry);

tlabConfiguration->usesTLABs = mmFuncs->j9gc_is_tlab_enabled(vm);
tlabConfiguration->minTLABSize = mmFuncs->j9gc_get_tlh_minimum_size(vm);
/* The closest OMR equivalent to tlabRefillWasteLimit is the
* initial value of abandonSize in TLHAllocationSupport::refresh(), which
* evaluates to max(tlhMinimumSize, tlhInitialSize / 2) on a fresh thread.

@amicic amicic Jul 14, 2026 •
edited
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This is not a correct interpretation - the waste is roughly 1/2 of refresh size, because current refresh size typically dominates over initial/minimum

The hard part is that the refresh size is local to each allocating thread

For fast allocating threads refresh size is close to tlhMaximumSize, and for slow allocating it's close to tlhMinimumSize

If we want to generalize, we can say refresh is tlhMaximumSize across VM, in which case the waste limit is 1/2 of that. More correct would be to account for the largest refresh of all allocating threads (what would require to walk over all threads at the moment of the API invocation).

It may be relevant for X platforms where tlhMaximumSize defaults to 1MB, and is not always reached (by refresh). On other platforms were it defaults to 128KB it's pretty much always reached.

* We report tlhInitialSize / 2 as it dominates once refreshSize >= tlhInitialSize.
*/
tlabConfiguration->tlabRefillWasteLimit = mmFuncs->j9gc_get_tlh_initial_size(vm) / 2;
}

static uintptr_t recordSystemProcessEvent(uintptr_t pid, const char *commandLine, void *userData)
{
VM_JFRConstantPoolTypes *constantPoolTypes = reinterpret_cast<VM_JFRConstantPoolTypes *>(userData);
Expand Down Expand Up @@ -2246,6 +2283,7 @@ class VM_JFRConstantPoolTypes {
, _shouldWriteModuleRequire(false)
, _shouldWriteModuleExport(false)
, _shouldWriteClassLoaderStatistics(false)
, _shouldWriteGCTLABConfigurationEvent(false)
, _previousStackTraceEntry(NULL)
, _firstStackTraceEntry(NULL)
, _previousThreadEntry(NULL)
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1 change: 1 addition & 0 deletions runtime/vm/JFRPeriodic.hpp
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Expand Up @@ -53,6 +53,7 @@ class JfrPeriodicEventSet {
static void requestThreadDump(J9VMThread *currentThread);
static void requestVirtualizationInformation(J9VMThread *currentThread);
static void requestYoungGenerationConfiguration(J9VMThread *currentThread);
static void requestGCTLABConfiguration(J9VMThread *currentThread);
};

#endif /* !defined(JFRPERIODIC_HPP_) */
13 changes: 13 additions & 0 deletions runtime/vm/jfr.cpp
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Expand Up @@ -203,6 +203,7 @@ jfrEventSize(J9JFREvent *jfrEvent)
case J9JFR_EVENT_TYPE_MODULE_EXPORT:
case J9JFR_EVENT_TYPE_CLASS_LOADER_STATISTICS:
case J9JFR_EVENT_TYPE_NATIVE_LIBRARY:
case J9JFR_EVENT_TYPE_GC_TLAB_CONFIGURATION:
size = sizeof(J9JFREvent);
break;
default:
Expand Down Expand Up @@ -2234,6 +2235,9 @@ JfrPeriodicEventSet::requestEvent(J9VMThread *currentThread, jlong id)
case JfrYoungGenerationConfigurationEvent:
requestYoungGenerationConfiguration(currentThread);
break;
case JfrGCTLABConfigurationEvent:
requestGCTLABConfiguration(currentThread);
break;
default:
return JNI_FALSE;
}
Expand Down Expand Up @@ -2469,6 +2473,15 @@ jfrThreadAllocationStatisticsCallback(J9VMThread *currentThread, IDATA handlerKe
}

}

void
JfrPeriodicEventSet::requestGCTLABConfiguration(J9VMThread *currentThread)
{
J9JFREvent *jfrEvent = (J9JFREvent *)reserveBuffer(currentThread, currentThread, sizeof(J9JFREvent));
if (NULL != jfrEvent) {
initializeEventFields(currentThread, currentThread, jfrEvent, J9JFR_EVENT_TYPE_GC_TLAB_CONFIGURATION);
}
}
#endif /* JAVA_SPEC_VERSION >= 17 */

void
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9 changes: 9 additions & 0 deletions test/functional/cmdLineTests/jfr/jfrevents.xml
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Expand Up @@ -87,6 +87,15 @@ SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0-only WITH Classpath-ex
<output type="success" caseSensitive="yes" regex="no">jdk.YoungGenerationConfiguration</output>
<output type="failure" caseSensitive="yes" regex="no">jfr print: could not read recording</output>
</test>
<test id="test jfr GC TLAB configuration - approx 30seconds">
<command>$JFR_EXE$ print --xml --events "GCTLABConfiguration" defaultJ9recording.jfr</command>
<output type="required" caseSensitive="yes" regex="no">http://www.w3.org/2001/XMLSchema-instance</output>
<output type="success" caseSensitive="yes" regex="no">jdk.GCTLABConfiguration</output>
<output type="required" caseSensitive="yes" regex="no">usesTLABs</output>
<output type="required" caseSensitive="yes" regex="no">minTLABSize</output>
<output type="required" caseSensitive="yes" regex="no">tlabRefillWasteLimit</output>
<output type="failure" caseSensitive="yes" regex="no">jfr print: could not read recording</output>
</test>
<test id="test jfr system process - approx 30 seconds">
<command>$JFR_EXE$ print --xml --events "SystemProcess" defaultJ9recording.jfr</command>
<output type="required" caseSensitive="yes" regex="no">http://www.w3.org/2001/XMLSchema-instance</output>
Expand Down