compressed oops and 64-bit header words

[Dan Grove]

Hi-

I talked some with the Nikolay Igotti about compressed oops in
OpenJDK7. He tells me that the mark word and class pointer remain 64
bits when compressed oops are being used. It seems that this leaves a
fair amount of the bloat in place when moving from 32->64 bits.

I'm interesting in deprecating 32-bit VM's at my employer at some
point. Doing this is going to require that 64-bit VM's have as little
bloat as possible. Has there been any consideration of making the mark
word and class pointer 32 bits in cases where the VM fits within 4GB?
It seems like this would be a major win. A second benefit here is that
the "add and shift" currently required on dereference of compressed
oops could be eliminated in cases where the VM fit inside 4GB.

Dan