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attempt to share loader for JIT-ed classes #5880

merged 2 commits into from Sep 27, 2019

attempt to share loader for JIT-ed classes #5880

merged 2 commits into from Sep 27, 2019


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@kares kares commented Sep 17, 2019

introduces a -Xjit.loader.mode which is either UNIQUE (default), SHARED or SHARED_SOURCE

most of it is making WeakValueMap implement Map as I originally did something else here ...
so I've kept that code and just did a fake Map for the single (shared) global class-loader.
that can be changed as needed to a cleaner (proper oop) way.

the SHARED_SOURCE was so far only tested with jruby's test suite, the JITed class-loader count went down to 10% ... and meta-space was much less fragmented - saving around 8% of allocated space.

was not sure whether we should attempt to somehow detect eval-ed pieces
and not share them with the same source file but rather always on their own?
given that SHARED_SOURCE isn't changed to be the new default, we can also decide later.

also if you have suggestions for better naming the option or the enum values.

@kares kares changed the title an attempt to share loader for JIT-ed classes attempt to share loader for JIT-ed classes Sep 17, 2019
@kares kares requested review from headius and enebo Sep 20, 2019
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@headius headius left a comment

This all seems good to me!

I don't know what to say about eval methods; in order for them to be a problem, they'd have to:

  • Be continually generated at runtime. This is very uncommon.
  • Be called enough to JIT. This seems unlikely now and even more unlikely with our time-based threshold changes.

On the flip side, many methods get generated using eval in a "safe" way (only once, usually to lazily metaprogram some methods) and we definitely want those to be eligible for JIT without a whole separate classloader (when running in a shared mode).

I think we go with this for now as-is. Folks that opt into shared classloading can help us uncover any weird eval edge cases.

enebo approved these changes Sep 26, 2019
@kares kares added this to the JRuby milestone Sep 27, 2019
@kares kares added the jit label Sep 27, 2019
either for every JIT-ed class or based on source file
@kares kares merged commit a88704f into master Sep 27, 2019
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3 participants