Direct promotion to old gen

Tony Printezis Antonios.Printezis at sun.com
Mon Aug 3 11:41:05 PDT 2009



Peter B. Kessler wrote:
> Tony Printezis wrote:
>> Sujit,
>>
>> Sujit.Das at cognizant.com wrote:
>>> Hi All,
>>>  
>>> I am trying to capture statistics to denote direct promotion from 
>>> young gen to old gen.
>>>  
>>> ....
>>> Anything more than previous age4 size is result of direct promotion 
>>> from eden space to old gen.
>> It is possible that objects with a younger age than MTT (4, in this 
>> case, to be promoted). If, during GC, the survivor space overflows 
>> then we have to promote everything else (not only objects from the 
>> eden, but also objects from the from survivor space with younger ages).
>> ....
>
> A minor correction:  I'm pretty sure that one object failing to fit in 
> to-space doesn't imply that all further attempts will result in 
> promotion.  E.g., if you have one big object that fails to fit in the 
> to-space, then it will be put in the old-space, but after that smaller 
> objects may well fit in the to-space so we will put them there.  That 
> is, each object is considered individually: if the policy says we 
> should put it in the old generation then we do, but otherwise we try 
> to put it in the to-space.  If it fits, we're happy, if it doesn't fit 
> we put it in the old generation.
Yes, this is absolutely correct Peter. Thanks.

Tony
> The point of the age bits and the tenuring threshold policy is to 
> advise us which relatively older objects should be promoted so that 
> there's room for the relatively younger objects to fit in the 
> to-space.  We need a policy like that because we don't consider the 
> objects in age order.
>
>             ... peter

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