CRR (S/M): 6994322: Remove the is_tlab and is_noref / is_large_noref parameters from the CollectedHeap interface

[Tony Printezis]

Hi all,

This is the one you've all been waiting for. :-) I'd like a couple of 
code reviews for this change:

http://cr.openjdk.java.net/~tonyp/6994322/webrev.0/

It removes two parameters from the mem_allocate() method and updates its 
implementations and uses. The two parameters are the following.

a) is_tlab : indicates whether the allocation is for a TLAB or not. 
However, given that all TLAB allocations go through the 
allocate_new_tlab() method, all calls to mem_allocate() have is_tlab == 
false. (Note: in G1 we have had an assert that checks that !is_tlab for 
a few months now without any failures.) So, having the is_tlab parameter 
seems pointless.

b) is_noref (also called: is_large_noref) : indicates that the 
allocation is for a large scalar object (and in particular: an array). 
The large_typearray_limit() method specifies how large such an object 
should be and, based on this value, the allocation goes through either 
array_allocate() or large_typearray_allocate(), the only difference 
between the two is the value of the is_noref parameter that's passed to 
the allocate_routines. However, all mem_allocate() implementations just 
ignore that parameter (we think it's some baggage we're still carrying 
from the Train GC!!!).

The changes for a) were trivial for G1 and the framework GCs but a bit 
more involved for PS given that the is_tlab parameter is propagated 
through a few methods and a VM operation. But note that none of those 
are actually called from allocate_new_tlab(), so it's safe to assume 
that they are only called for non-TLAB allocations. I did go over that 
code very carefully to convince myself that this is the case and I don't 
see any flaws. I would appreciate if someone else also does that just in 
case...

The changes for b) were trivial overall, given that the is_noref 
parameter was not actually used by any of the GCs. So I just had to 
remove the large_typearray_limit() and large_typearray_allocate()methods.

I tested this workspace with our GCs and I haven't seen any issues. And 
please let me know if there are any concerns about this.

Tony