RFR: 8349713: [leyden] Memory map the cached code file [v3]

[Aleksey Shipilev]

On Wed, 12 Feb 2025 10:33:46 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> It is visible in profiles for lots of applications that reading the SC cache file at startup costs significantly. On JavacBenchApp example, loading ~25M code requires about 30ms. This is ~1 GB/sec, so it is I/O limited.
>> 
>> We should really mmap the SC cache file to alleviate these costs. Let the actual SC readers (separate threads) to eat the cost of reading from the backing file. 
>> 
>> I was not entirely sure COW for file mappings works correctly on Windows, so I excepted that one.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, `runtime/cds`
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Remove flag, allow all platforms, remove C-heap load
>  - Merge branch 'premain' into JDK-8349713-mmap-sccache
>  - Merge branch 'premain' into JDK-8349713-mmap-sccache
>  - Fix

All right, the flag stays for a while. Once Ashu moves this whole thing to CDS, we can remove the flag. Meanwhile, we only do mmap on Linux. I think we are ready to integrate this.

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PR Comment: https://git.openjdk.org/leyden/pull/34#issuecomment-2654010848