Request for review 8007320: NPG: move method annotations

[John Rose]

On Jan 31, 2013, at 4:02 PM, Jiangli Zhou <jiangli.zhou at oracle.com> wrote:

> I wonder if the AnnotationArray pointers could be eliminated by embedding the raw annotation data in ConstMethod directly. The ConstMethod::_flags could still be kept as 8-bit, with one bit to indicate if the method has any type of the annotations.

Using a bitmask is a good step.  We should package up this sort of trick so that it can be widely used in the JVM.  (See below.)

Beyond that, squishing 80%+ of all numbers down to a single byte would be the real pay-off.  That's what compressed streams do for debug information, and they should be used routinely for class metadata also.

There's no reason our metadata has to be so full of null bytes.  A large percentage of u2 and u4 words have nulls.  Down with entropy!

(Beyond that, making things sharable across processes, and/or using zip, would stack on more 2x-5x improvements.  Those two techniques amount to global and local duplicate removal.)

Check out this prototype (previously posted) for bundling together bytestreams in metadata:

http://mail.openjdk.java.net/pipermail/hotspot-dev/2013-January/007807.html
https://blogs.oracle.com/jrose/resource/hotspot/streamBundle.patch.zip

The stream-bundle approach would allow "null-heavy" data like untransformed annotations to be stored as-is.  It would also encourage the use of more compact formats.

— John
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