RFR (S): 8200385: Eagerly reclaimed humongous objects leave mark in prev bitmap

Thomas Schatzl thomas.schatzl at oracle.com
Mon Apr 9 17:23:37 UTC 2018


Hi Sangheon,

On Mon, 2018-04-09 at 09:32 -0700, sangheon.kim wrote:
> Hi Thomas,
> 
> On 04/06/2018 10:58 AM, Thomas Schatzl wrote:
> > Hi,
> > 
> >    could a second person look at this please?
> > 
> > Thanks,
> >    Thomas
> > 
> > On Thu, 2018-03-29 at 11:12 +0200, Thomas Schatzl wrote:
> > > Hi all,
> > > 
> > >    can I have reviews for this small fix to a benign bug, that is
> > > I
> > > haven't seen any actual product failure from it but some very
> > > rare
> > > test
> > > failures, where when we eagerly reclaim humongous objects we
> > > leave a
> > > mark on the prev bitmap in some cases?
> > > 
> > > The suggested fix is to always look at the prev bitmap and clear
> > > it,
> > > and if needed also clear potential marks in the next bitmap.
> > > 
> > > To make the failure appear basically 100% in that test, I added a
> > > simple assert after reclaiming the humongous object.
> > > 
> > > With the fix, this failure goes away completely.
> > > 
> > > Note that this is more a "data structure hygiene" fix - the stray
> > > mark
> > > on the prev bitmap will be automatically cleared after switching
> > > the
> > > bitmaps at cleanup and preparing that bitmap for the next mark.
> > > 
> > > CR:
> > > https://bugs.openjdk.java.net/browse/JDK-8200385
> > > Webrev:
> > > http://cr.openjdk.java.net/~tschatzl/8200385/webrev/
> 
> Webrev.1 looks good.
> 

  thank you for your review.

Thomas



More information about the hotspot-gc-dev mailing list