RFR: Fix ShFreeSet boundary case

[Aleksey Shipilev]

On 05/10/2018 04:42 PM, Aleksey Shipilev wrote:
> On 05/09/2018 09:30 PM, Roman Kennke wrote:
>> Observed with the new PLAB code. Apparently this triggers the situation fairly often because it
>> tends to allocate region sized GCLABs.
But this is also suspicious: we used to cap the TLAB sizes below region size to avoid fragmentation.
This does not happen with PLABs? Should probably adjust that part.

-Aleksey