RFR(s): 6764713: Enlarge the age field in object headers to allow a higher MaxTenuringThreshold
tom.benson at oracle.com
Fri Feb 13 17:16:15 UTC 2015
Note that not taking this bit for the age field would open the door to
reducing the alignment of the JavaThread*. It's the fact that there was
already an unclaimed bit there (in the 64-bit version) that made the age
size increase seem more reasonable.
However, I'd propose not changing that, either, at least for the 64-bit
version, so that when someone finally claims "the bit" it doesn't need
to be undone. For the 32-bit version, it's less clear cut, but I'd
still lean toward leaving it as is.
On 2/13/2015 11:37 AM, Bengt Rutisson wrote:
> On 2015-02-13 16:37, Tom Benson wrote:
>> Based on comments here and elsewhere on possible future uses for this
>> unused bit (in the 64-bit version), I'm more inclined to close both
>> 6764713 and 6719225 with no change. With a comment along the lines
>> of "evolution of the JVM since the time the age field was reduced has
>> revealed potentially more valuable uses of the bit."
> This sounds like a good approach in my view. I think we can leave the
> age at 4 bits. In my view the main issue with the aging is that our
> heuristics for adjusting the tenuring threshold are not always
> reliable. Sometimes the threshold gets stuck at the max value etc. I
> prefer to close these bug reports as suggested above and if we want to
> improve the tenuring we should work on the heuristics instead.
> Thanks for digging these bug reports up, Tom! We should probably have
> brought them up for discussion and closing them a long time ago.
>> However, if there are supporters of a larger MaxTenuringThreshold
>> lurking, I'd like to hear their point of view as well.
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