RFR: 8293499: Provide jmod compression level option

[Aleksey Shipilev]

On Mon, 12 Sep 2022 10:15:26 GMT, Jaikiran Pai <jpai 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". (Separately, we could argue if 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."?

Right. Done in new commit (to be published soon).

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