Request for review 8007320: NPG: move method annotations

[Jiangli Zhou]

Hi John,

On 02/01/2013 11:36 AM, John Rose wrote:
> On Jan 31, 2013, at 4:02 PM, Jiangli Zhou <jiangli.zhou at oracle.com 
> <mailto: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.

Yes! Using a bitmask is even better than using 1-byte for each type 
inside the stream. I think the definitely utilize the  stream-bundle 
approach.

Thanks!
Jiangli
>
> — John

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