Request for review 8007320: NPG: move method annotations

[Jiangli Zhou]

On 02/04/2013 04:48 PM, Coleen Phillimore wrote:
> On 2/1/2013 3:11 PM, Jiangli Zhou wrote:
>> 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.
>
> We should talk about this as an improved technique for bundling 
> metadata.  I did read through the code (and have it in this 
> repository) but I think it's a bigger project to adapt it than what 
> I've done.

Ok.

Thanks,
Jiangli

> Thanks,
> Coleen
>
>>
>> Thanks!
>> Jiangli
>>>
>>> — John
>>
>

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