RFR (XS): 8140597: Initial mark caused by humongous allocations can prevent mixed collections

[Thomas Schatzl]

Hi,

  let me retract this RFR for a short while. I noticed that this is a
general problem with any event that tries to force an initial mark.

I need some time to test a change I have that fixes the problem for all
these events.

Thanks,
  Thomas

On Wed, 2015-10-28 at 21:29 +0100, Thomas Schatzl wrote:
> Hi all,
> 
>   can I have reviews for this bug in the GC state machinery that results
> in mixed collections being completely skipped if an initial mark caused
> by humongous allocation occurs between the end of marking activity and
> before the last young-only gc that should initiate the mixed phase?
> 
> Basically the initial mark request overrides the transition from that
> last young-only GC to the mixed gc.
> 
> There is a really detailed technical description about what happens in
> the CR.
> 
> This behavior is really problematic in case you tuned (either manually
> or automatically) the IHOP to the latest possible time to start marking.
> 
> This seems like a bug that has been in since at least 2010.
> 
> I also changed the code to actually assert if G1 tries to do an initial
> mark in the last young gc before the mixed phase. That restriction may
> be lifted in a later change again (i.e. if G1 notices that there is
> nothing to reclaim at the start of that last young-only gc). But that is
> another change :)
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8140597
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8140597/webrev/
> Testing:
> jprt, vm.gc testlist, manual testing with the mentioned existing test in
> the CR
> 
> Thanks,
>   Thomas
>