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SapMachine (21) #2250: Add adjustments to heap dumps for the buildpack #2281

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SapMachine (21) #2250: Add adjustments to heap dumps for the buildpack #2281

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0e7ffc5
Add heap dump features for buildpack.
schmelter-sap Jun 16, 2026
4540de9
Test improvements.
schmelter-sap Jun 17, 2026
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32 changes: 32 additions & 0 deletions src/hotspot/share/runtime/globals.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -711,6 +711,38 @@ const int ObjectAlignmentInBytes = 8;
"compression. Otherwise the level must be between 1 and 9.") \
range(0, 9) \
\
/* SapMachine 2026-06-16: Allow to overwrite the heap dump file. */ \
product(bool, HeapDumpOverwrite, false, MANAGEABLE, \
"If enabled, the heap dump on out of memory error can " \
"overwrite an already existing file.") \
\
/* SapMachine 2026-06-16: For upward compatibility. */ \
product(uint, HeapDumpParallelism, 0, MANAGEABLE, \
"This is ignored.") \
range(0, 100000) \
\
/* SapMachine 2026-06-16: Allow to skip content of arrays in dumps.*/ \
product(bool, LimitPrimitiveArrayContentInHeapDump, false, MANAGEABLE, \
"If enabled, the content of primitive arrays is not completely " \
"written to a heap dump for large arrays. Note that this only " \
"really saves space, if the compression of the heap dump is " \
"enabled too, since the skipped elements are written as " \
"0 or false.") \
\
/* SapMachine 2026-06-16: Allow to skip content of arrays in dumps.*/ \
product(int, StringLikeContentSizeLimitInHeapDump, 120, MANAGEABLE, \
"The number of entries in primitive char and byte arrays to " \
"not skip in a heap dump when " \
"LimitPrimitiveArrayContentInHeapDump is enabled.") \
range(0, 100000) \
\
/* SapMachine 2026-06-16: Allow to skip contents of arrays in dumps.*/ \
product(int, ArrayContentSizeLimitInHeapDump, 50, MANAGEABLE, \
"The number of entries in a primitive array other than char and " \
"byte arrays to not skip in a heap dump when " \
"LimitPrimitiveArrayContentInHeapDump is enabled.") \
range(0, 100000) \
\
product(ccstr, NativeMemoryTracking, DEBUG_ONLY("summary") NOT_DEBUG("off"), \
"Native memory tracking options") \
\
Expand Down
51 changes: 49 additions & 2 deletions src/hotspot/share/services/heapDumper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -436,6 +436,8 @@ class AbstractDumpWriter : public StackObj {
void write_symbolID(Symbol* o);
void write_classID(Klass* k);
void write_id(u4 x);
// SapMachine 2026-06-16: Writes zeros to the buffer.
void write_zero(size_t len);

// Start a new sub-record. Starts a new heap dump segment if needed.
void start_sub_record(u1 tag, u4 len);
Expand Down Expand Up @@ -543,6 +545,26 @@ void AbstractDumpWriter::write_id(u4 x) {
#endif
}

// SapMachine 2026-06-16: Writes zeros to the buffer.
void AbstractDumpWriter::write_zero(size_t len) {
assert(!_in_dump_segment || (_sub_record_left >= len), "sub-record too large");
DEBUG_ONLY(_sub_record_left -= len);

// flush buffer to make room.
while (len > buffer_size() - position()) {
assert(!_in_dump_segment || _is_huge_sub_record,
"Cannot overflow in non-huge sub-record.");
size_t to_write = buffer_size() - position();
memset(buffer() + position(), 0, to_write);
len -= to_write;
set_position(position() + to_write);
flush();
}

memset(buffer() + position(), 0, len);
set_position(position() + len);
}

// We use java mirror as the class ID
void AbstractDumpWriter::write_classID(Klass* k) {
write_objectID(k->java_mirror());
Expand Down Expand Up @@ -1531,6 +1553,24 @@ void DumperSupport::dump_prim_array(AbstractDumpWriter* writer, typeArrayOop arr
return;
}

// SapMachine 2026-06-16: If enabled, we don't dump the whole content of large arrays, but just the start
// and fill the rest with zeroes.
int fill_with_zero = 0;

if (LimitPrimitiveArrayContentInHeapDump) {
int limit = ArrayContentSizeLimitInHeapDump;

if (type == T_BYTE || type == T_CHAR) {
limit = StringLikeContentSizeLimitInHeapDump;
}

if (length > limit) {
fill_with_zero = length - limit;
length = limit;
length_in_bytes = (u4)length * type_size;
}
}

// If the byte ordering is big endian then we can copy most types directly

switch (type) {
Expand Down Expand Up @@ -1598,6 +1638,11 @@ void DumperSupport::dump_prim_array(AbstractDumpWriter* writer, typeArrayOop arr
default : ShouldNotReachHere();
}

// SapMachine 2026-06-16: Fill with zeros, if we don't dump the whole content of the array.
if (fill_with_zero > 0) {
writer->write_zero((u4)fill_with_zero * type_size);
}

writer->end_sub_record();
}

Expand Down Expand Up @@ -2621,7 +2666,8 @@ void HeapDumper::set_error(char const* error) {
// outside of a JVM safepoint
void HeapDumper::dump_heap_from_oome() {
// SapMachine 2024-05-10: HeapDumpPath for jcmd
HeapDumper::dump_heap(false, true);
// SapMachine 2026-06-16: Handle HeapDumpOverwrite
HeapDumper::dump_heap(false, true, tty, -1, HeapDumpOverwrite);
}

// Called by error reporting by a single Java thread outside of a JVM safepoint,
Expand All @@ -2631,7 +2677,8 @@ void HeapDumper::dump_heap_from_oome() {
// inteference when updating the static variables base_path and dump_file_seq below.
void HeapDumper::dump_heap() {
// SapMachine 2024-05-10: HeapDumpPath for jcmd
HeapDumper::dump_heap(false, false);
// SapMachine 2026-06-16: Handle HeapDumpOverwrite
HeapDumper::dump_heap(false, false, tty, -1, HeapDumpOverwrite);
}

// SapMachine 2024-05-10: HeapDumpPath for jcmd
Expand Down
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