8332139: SymbolTableHash::Node allocations allocates twice the required memory

[xmas92]

The symbols are inline and allocated together with the ConcurrentHashTable (CHT) Nodes. The calculation used for the required size is alloc_size = size + value.byte_size() + value.effective_length();

Where

• size == sizeof(SymbolTableHash::Node) == sizeof(void*) + sizeof(Symbol)
• value.byte_size() == dynamic_sizeof(Symbol) == sizeof(Symbol) + <bytes beyond object>
• value.effective_length() == dynamic_sizeof(Symbol) - sizeof(Symbol) == <bytes beyond object>

So alloc_size ends up being sizeof(void*) /* node metadata */ + 2 * dynamic_sizeof(Symbol)

Because using the CHT with dynamically sized (and inlined) types requires knowing about its implementation details I chose to make the functionality for calculating the the allocation size a property of the CHT. It now queries the CHT for the node allocation size given the dynamic size required for the VALUE.

The only current (implicit) restriction regarding using dynamically sized (and inlined) types in CHT is that the _value field C++ object ends where the Node object ends, so there is not padding bytes where the dynamic payload is allocated. (effectively sizeof(VALUE) % alignof(Node) == 0 as long as there are no non-standard alignment fields in the Node metadata). I chose to test this as a runtime assert that the _value ends where the Node object ends, instead of a static assert with the alignment as it seemed to more explicitly show the intent of the check.

Running testing tier1-7

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Issue

• JDK-8332139: SymbolTableHash::Node allocations allocates twice the required memory (Bug - P4)

Reviewers

• Ivan Walulya (@walulyai - Reviewer)

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8332139: SymbolTableHash::Node allocations allocates twice the required memory

Reviewed-by: iwalulya

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At the time when this comment was updated there had been 131 new commits pushed to the master branch:

• 0a9d1f8: 8332749: Broken link in MemorySegment.Scope.html
• c9a7b97: 8332829: [BACKOUT] C2: crash in compiled code because of dependency on removed range check CastIIs
• 7fd9d6c: 8332340: Add JavacBench as a test case for CDS
• 417d174: 8331348: Some incremental builds deposit files in the make directory
• 303ac9f: 8332671: Logging for pretouching thread stacks shows wrong memory range
• 90758f6: 8332808: Always set java.io.tmpdir to a suitable value in the build
• e19a421: 8332720: ubsan: instanceKlass.cpp:3550:76: runtime error: member call on null pointer of type 'struct Array'
• 2581935: 8332528: Generate code in SwitchBootstraps.generateTypeSwitch that require fewer adaptations
• b890336: 8328083: degrade virtual thread support for GetObjectMonitorUsage
• 4e6d851: 8325324: Implement JEP 477: Implicitly Declared Classes and Instance Main Methods (Third Preview)
• ... and 121 more: https://git.openjdk.org/jdk/compare/5a8df4106ac5386eb72e874dcadf2b18defe27d8...master

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[walulyai]

LGTM!