RFR: JDK-8211150: G1 Full GC not purging code root memory and hence causing memory leak

[Thomas Schatzl]

Hi Poonam,

On Mon, 2018-10-01 at 09:39 -0700, Poonam Parhar wrote:
> Hello,
> 
> Please review this simple code change that fixes a memory leak during
> the G1 Full GC cycle.
> 
> JDK-8211150: G1 Full GC not purging code root memory and hence
> causing memory leak
> 
> Webrev: http://cr.openjdk.java.net/~poonam/8211150/webrev/
> 
> Problem and fix: During G1 Full collections, the code root memory is
> not being deallocated, and that causes a leak for processes invoking
> only Full GCs (e.g. using System.gc()). The above change fixes that
> leak. Please see the attached images showing the memory allocations
> of a process creating lots of Thread objects and invoking
> System.gc(), before and after this fix. The allocations profile is
> collected using jemalloc. Before-fix image clearly shows that the new
> entries created in G1CodeRootSetTableEntry are not being deleted in
> Full collections.

  while the change is correct, I would expect that placing the
purge_code_root_memory() call after the rebuild_strong_code_roots()
call, as otherwise to-be-purged objects created during that time would
carry over to the next GC. I.e. needlessly keep them alive.

Thanks,
  Thomas