RFR: 8293499: Provide jmod compression level option

[Jaikiran Pai]

On Thu, 8 Sep 2022 07:57:36 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> I have been looking into `make clean-images images` performance, and realized jmod keeps compressing files with default compression level. Tuning that toward lighter compression levels improves build performance considerably, without a heavy loss in *.jmod sizes. 
> 
> This PR allows JMOD to select the compression level. Follow-ups would use this in the build system, see #10214.
> 
> This change nominally requires CSR, but I would like to gauge the reaction to this patch first, before submitting a formal CSR. The interesting asymmetry against `jlink` is: `jlink` provides `--compress` option that only takes `2` for "ZIP compression". I would argue it would be beneficial to add `--compression-level` to `jlink` as well, so to select the compression level there too.

src/jdk.jlink/share/classes/jdk/tools/jmod/resources/jmod.properties line 85:

> 83: main.opt.cmdfile=Read options from the specified file
> 84: 
> 85: main.opt.compression-level=Compression level to use when compressing the JMOD archive.\

Hello Aleksey, should this instead say "Compression level to use when creating the JMOD archive."?

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PR: https://git.openjdk.org/jdk/pull/10213