RFR: 8334231: Optimize MethodData layout

[Xiaolong Peng]

On Thu, 4 Jul 2024 11:25:39 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> Hi all,
>>      This PR is a part of https://bugs.openjdk.org/browse/JDK-8334227 to optimize Hotspot C++ class layouts, this one is for the layout of  MethodData. Here is the original layout from `pahole`:
>> 
>> class MethodData : public Metadata {
>> public:
>> 
>> 	/* class Metadata            <ancestor>; */      /*     0     0 */
>> 
>> 	/* XXX 8 bytes hole, try to pack */
>> 
>> 	class Method *             _method;              /*     8     8 */
>> 	int                        _size;                /*    16     4 */
>> 	int                        _hint_di;             /*    20     4 */
>> 	class Mutex               _extra_data_lock;      /*    24   104 */
>> 	/* --- cacheline 2 boundary (128 bytes) --- */
>> 	class CompilerCounters    _compiler_counters;    /*   128    80 */
>> 	/* --- cacheline 3 boundary (192 bytes) was 16 bytes ago --- */
>> 	intx                       _eflags;              /*   208     8 */
>> 	intx                       _arg_local;           /*   216     8 */
>> 	intx                       _arg_stack;           /*   224     8 */
>> 	intx                       _arg_returned;        /*   232     8 */
>> 	int                        _creation_mileage;    /*   240     4 */
>> 	class InvocationCounter   _invocation_counter;   /*   244     4 */
>> 	class InvocationCounter   _backedge_counter;     /*   248     4 */
>> 	int                        _invocation_counter_start; /*   252     4 */
>> 	/* --- cacheline 4 boundary (256 bytes) --- */
>> 	int                        _backedge_counter_start; /*   256     4 */
>> 	uint                       _tenure_traps;        /*   260     4 */
>> 	int                        _invoke_mask;         /*   264     4 */
>> 	int                        _backedge_mask;       /*   268     4 */
>> 	short int                  _num_loops;           /*   272     2 */
>> 	short int                  _num_blocks;          /*   274     2 */
>> 	enum WouldProfile          _would_profile;       /*   276     4 */
>> 	int                        _jvmci_ir_size;       /*   280     4 */
>> 
>> 	/* XXX 4 bytes hole, try to pack */
>> 
>> 	class FailedSpeculation *  _failed_speculations; /*   288     8 */
>> 	int                        _data_size;           /*   296     4 */
>> 	int                        _parameters_type_data_di; /*   300     4 */
>> 	int                        _exception_handler_data_di; /*   304     4 */
>> 
>> 	/* XXX 4 bytes hole, try to pack */
>> 
>> 	intptr_t                   _data[1];             /*   312     8 */
>> 
>> 	/* size: 320, cachelin...
>
> Looks good to me, too. Yes, I think this is trivial.

Thank you for the review! @chhagedorn

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PR Comment: https://git.openjdk.org/jdk/pull/20019#issuecomment-2208737190