[PATCH] enhancement to ParallelScavenge Full GC

Thomas Schatzl thomas.schatzl at oracle.com
Mon Dec 14 16:49:46 UTC 2015


On Mon, 2015-12-14 at 23:57 +0800, ray alex wrote:
> Thanks, Thomas!
> I will refine my code carefully according to your suggestions as soon
> as possible.

> Since I'm new in contributing to OpenJDK, actually I'm not sure how to
> upload when my new code is ready?
>  Just upload an attach of diffs as I did, or some other ways?

The best way as long as we have no confirmation about the OCA signing,
is to attach a patch (or a webrev, see
http://openjdk.java.net/contribute/) and send it to this list. Later it
will be more convenient to send me a patch that I will convert into a
webrev and put on cr.openjdk.java.net.

As soon as you have two contributions, you can upload patches yourselves
onto your own account on cr.openjdk.java.net.
> Besides, I'm currently processing my signed OCA for the committer
> rights, 
> I'm not sure how long it will take, does it matter?

The OCA is only for us to be able to accept your patch in Hotspot. The
various levels of contributor status are a different matter, and signify
your level of expertise within the community.

See also http://openjdk.java.net/contribute/ for more information.

> As for the VM Thread, it does a serial adjust_roots() within the
> current thread (VM thread) during
> PSParallelCompact::invoke_no_policy().
>  I think psCompactionManager.cpp:117 and the surrounding comments
> confirm the use of VMThread in full GC.
> Do you agree with my above understanding of the use of VMThread?
You are right :(

There are multiple options to provide an additional per-thread context:

- passing around some context. Looks like lots of work.
- change the code so that even that serial portion is performed by some
GCTaskThread (which actually sounds best to me)
- Another would be to add a field to both GCTaskThread and VMThread, and
via a virtual method in Thread get the necessary values.
- make VMThread a WorkerThread (that has an id that can be used to query
an extra data structure for this cache)
- others

Let's see if other people have a better idea.


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