JEP 147: Reduce Class Metadata Footprint

[David Holmes]

On 1/03/2012 7:33 PM, Florian Weimer wrote:
> * David Holmes:
>
>> On 1/03/2012 5:49 PM, Florian Weimer wrote:
>>>> Posted: http://openjdk.java.net/jeps/147
>>>
>>> This part:
>>>
>>> |  - Limit the number of mallocs, and the resultant per-malloc block
>>> |    overhead, when allocating memory for a loaded class. Most of the
>>> |    class is laid out in one large malloc allocation.
>>>
>>> seems to overlap with JEP 122, which adds classloader-specific memory
>>> allocation pools.
>>
>> JEP 122 covers where the memory will be allocated. JEP 147 tackles how
>> much memory needs to be allocated.
>
> The per-object allocation overhead depends on where it is allocated.
> Depending on how the pool allocator works, reducing the number of
> allocations might no longer be necessary or even counterproductive (due
> to increased fragmentation).

The aim is simply to reduce the amount of memory needed, both in terms 
of the actual data of a class and the overhead in managing that data. If 
it turns out that permgen removal alleviates that overhead then that's 
great.

David