RFR: 8329433: Reduce nmethod header size [v4]

[Coleen Phillimore]

On Tue, 16 Apr 2024 03:31:25 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> This is part of changes which try to reduce size of `nmethod` and `codeblob` data vs code in CodeCache.
>> These changes reduced size of `nmethod` header from 288 to 232 bytes. From 304 to 248 in optimized VM:
>> 
>> Statistics for 1282 bytecoded nmethods for C2:
>>  total in heap = 5560352 (100%)
>>  header = 389728 (7.009053%)
>> 
>> vs
>> 
>> Statistics for 1322 bytecoded nmethods for C2:
>>  total in heap  = 8307120 (100%)
>>  header         = 327856 (3.946687%)
>> 
>> 
>> Several unneeded fields in `nmethod` and `CodeBlob` were removed. Some fields were changed from `int` to `int16_t` with added corresponding asserts to make sure their values are fit into 16 bits.
>> 
>> I did additional cleanup after recent `CompiledMethod` removal.
>> 
>> Tested tier1-7,stress,xcomp and performance testing.
>
> Vladimir Kozlov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use 16-bits types for header_size and frame_complete_offset arguments

src/hotspot/share/code/codeBlob.cpp line 106:

> 104: 
> 105: // Simple CodeBlob used for simple BufferBlob.
> 106: CodeBlob::CodeBlob(const char* name, CodeBlobKind kind, int size, uint16_t header_size) :

Just a drive-by comment.  You might be able to use delegating constructors for CodeBlob so you don't have to have the field initializations twice.  Maybe the same for nmethod ?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18768#discussion_r1567658758