On Sat, 27 Apr 2024 00:48:49 GMT, Dean Long <dl...@openjdk.org> wrote:
>> Move immutable nmethod's data from CodeCache to C heap. It includes
>> `dependencies, nul_chk_table, handler_table, scopes_pcs, scopes_data,
>> speculations, jvmci_data`. It amounts for about 30% (optimized VM) of space
>> in CodeCache.
>>
>> Use HotSpot's `os::malloc()` to allocate memory in C heap for immutable
>> nmethod's data. Bail out compilation if allocation failed.
>>
>> Shuffle fields order and change some fields size from 4 to 2 bytes to avoid
>> nmethod's header size increase.
>>
>> Tested tier1-5, stress,xcomp
>>
>> Our performance testing does not show difference.
>>
>> Example of updated `-XX:+PrintNMethodStatistics` output is in JBS comment.
>
> src/hotspot/share/code/nmethod.cpp line 1332:
>
>> 1330: #if INCLUDE_JVMCI
>> 1331: _speculations_offset = _scopes_data_offset;
>> 1332: _jvmci_data_offset = _speculations_offset;
>
> Why not use 0 for all these?
Right. Before all these offsets were assigned to _dependencies_offset which was
not 0.
But now we can use 0 for all of them since "_dependencies_offset" is 0.
> src/hotspot/share/code/nmethod.cpp line 1484:
>
>> 1482: // Calculate positive offset as distance between the start of
>> stubs section
>> 1483: // (which is also the end of instructions section) and the start
>> of the handler.
>> 1484: CHECKED_CAST(_unwind_handler_offset, int16_t, (_stub_offset -
>> code_offset() - offsets->value(CodeOffsets::UnwindHandler)));
>
> Suggestion:
>
> int unwind_handler_offset = code_offset() +
> offsets->value(CodeOffsets::UnwindHandler);
> CHECKED_CAST(_unwind_handler_offset, int16_t, _stub_offset -
> unwind_handler_offset);
Will do.
> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/code/NMethod.java line
> 528:
>
>> 526: private int getScopesDataOffset() { return (int)
>> scopesDataOffsetField .getValue(addr); }
>> 527: private int getScopesPCsOffset() { return (int)
>> scopesPCsOffsetField .getValue(addr); }
>> 528: private int getDependenciesOffset() { return (int) 0; }
>
> Suggestion:
>
>
> No longer used.
Will remove.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/18984#discussion_r1581667051
PR Review Comment: https://git.openjdk.org/jdk/pull/18984#discussion_r1581668080
PR Review Comment: https://git.openjdk.org/jdk/pull/18984#discussion_r1581679317
