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8334231: Optimize MethodData layout
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, cachelines: 5, members: 27 */
/* sum members: 304, holes: 3, sum holes: 16 */
};
There are 3 holes in the layout, the 1st 8-byte hole seems related to the ancestor Metadata which actually has 8-byte size, we may not be able to do anything to optimize:
class Metadata : public MetaspaceObj {
public:
/* class MetaspaceObj <ancestor>; */ /* 0 0 */
/* XXX last struct has 1 byte of padding */
int ()(void) * * _vptr.Metadata; /* 0 8 */
/* size: 8, cachelines: 1, members: 2 */
/* paddings: 1, sum paddings: 1 */
/* last cacheline: 8 bytes */
};
The two 4-byte holes should be easy to fix, we can simply swap the position of _jvmci_ir_size and _failed_speculations for better alignment. Here is the new layout after the change:
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 */
class FailedSpeculation * _failed_speculations; /* 280 8 */
int _jvmci_ir_size; /* 288 4 */
int _data_size; /* 292 4 */
int _parameters_type_data_di; /* 296 4 */
int _exception_handler_data_di; /* 300 4 */
intptr_t _data[1]; /* 304 8 */
/* size: 312, cachelines: 5, members: 27 */
/* sum members: 304, holes: 1, sum holes: 8 */
/* last cacheline: 56 bytes */
};
The two 4-byte holes are removed, saving 8 bytes.
Also removed unnecessary private: mark.
Additional test:
- [x] CONF=linux-x86_64-server-fastdebug CONF_CHECK=ignore make clean test TEST=tier2
Best, Xiaolong.
Progress
- [x] Change must be properly reviewed (1 review required, with at least 1 Reviewer)
- [x] Change must not contain extraneous whitespace
- [x] Commit message must refer to an issue
Issue
- JDK-8334231: Optimize MethodData layout (Sub-task - P4)
Reviewers
- David Holmes (@dholmes-ora - Reviewer)
Reviewing
Using git
Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/20019/head:pull/20019
$ git checkout pull/20019
Update a local copy of the PR:
$ git checkout pull/20019
$ git pull https://git.openjdk.org/jdk.git pull/20019/head
Using Skara CLI tools
Checkout this PR locally:
$ git pr checkout 20019
View PR using the GUI difftool:
$ git pr show -t 20019
Using diff file
Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/20019.diff
