RFR: 8204089: Timely Reducing Unused Committed Memory

[Thomas Schatzl]

Hi,

  at least one sentence needs further clarification.

On Thu, 2018-07-26 at 13:25 +0200, Thomas Schatzl wrote:
> Hi Rodrigo,
> 
>   first, sorry for taking so long to respond in this thread.
> 
[...]
> On Tue, 2018-06-19 at 20:46 +0200, Rodrigo Bruno wrote:
> > Hi all,
> > 
> > here is the first version of our contribution for draft JEP-
> > 8204089. 
> > 
> 
>   some comments:
> 
[...]
> - looking a bit at other implementations it might be worth to be able
> to customize what is been done when idle is detected.
> 
> In most cases it might be sufficient to just shrink the heap (in a
> new VM operation, using the existing code in
> G1CollectedHeap::resize_after_full_collection() that already uses
> Min/MaxHeapFreeRatio). A System.gc() seems very intrusive and should
> be optional imho after some thinking; making this optional does not
> seem too much work.
> 
> Consider applications with more than a few GB of heap, those will be
> affected a lot (i.e. unresponsive for multiple seconds)
> 
> A flag like UseFullGCForIdleCompaction(?) could be used here.
> 
> - the change does not make the system.gc() use "Idle" (probably "Idle
> Time Compaction") or similar as suggested in the JEP.

  ... as GC cause...

It is very important to make sure that this action is easily
identifiable for users.

Thanks,
  Thomas