RFR: 8048556: Unnecessary GCLocker-initiated young GCs

[Kim Barrett]

> On Jul 24, 2019, at 7:12 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
> When G1 has an allocation failure that might require a GC, and it
> can't satisfy the allocation in some other way (such as by allocating
> more young regions), then if GCLocker::needs_gc() is true it will
> stall and wait for the gc-locker gc request to be processed, and then
> retry the allocation.

Looking at the history of the G1 code, the present behavior of
deferring to a pending gc-locker gc request was introduced by

7143858: G1: Back to back young GCs with the second GC having a minimally sized eden

Sound familiar?  There are even comments in that CR discussing exactly
the race described by Tony in JDK-8048556.  Pity other GCs weren't
examined for the same problem and similarly modified at the same time.