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

[Vladimir Kozlov]

On Mon, 10 Feb 2025 12:14:11 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`

Good.  Until, as we discussed, cached code (and its data) will be part of CDS archive file.

How CDS handles `mmap` on windows?

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Marked as reviewed by kvn (Committer).

PR Review: https://git.openjdk.org/leyden/pull/34#pullrequestreview-2606244576