why this young gc is so slow?

[Igor Veresov]

How big are the survivor spaces (you can get this info by running with -XX:+PrintHeapAtGC)?

It seems that now it spends most of the time in steal-task, which is basically traversal of the subgraph that is in eden+survivor spaces and copying. 

igor

On Friday, August 19, 2011 at 8:12 PM, BlueDavy Lin wrote:

> I change the code,so avoid the old gen contains a huge data structure
> ref to young gen,now the ygc time reduce to about 40ms,live objects
> about 8m,but I think it should be faster than current,I'll see the
> code more detail.
> 
> current the gc task timestamps is:
> VM-Thread 298267312 298296585 298312254
> GC-Thread 0 entries: 11
>  [ old-to-young-roots-task 298267525 298267593 ]
>  [ old-to-young-roots-task 298267596 298267642 ]
>  [ thread-roots-task 298267643 298267664 ]
>  [ thread-roots-task 298267666 298267679 ]
>  [ thread-roots-task 298267680 298267688 ]
>  [ thread-roots-task 298267690 298267699 ]
>  [ thread-roots-task 298267703 298267713 ]
>  [ thread-roots-task 298267752 298267760 ]
>  [ thread-roots-task 298267762 298267768 ]
>  [ thread-roots-task 298267771 298267861 ]
>  [ steal-task 298267862 298296339 ]
> GC-Thread 1 entries: 6
>  [ thread-roots-task 298267623 298267739 ]
>  [ thread-roots-task 298267743 298267764 ]
>  [ thread-roots-task 298267766 298267775 ]
>  [ thread-roots-task 298267776 298267818 ]
>  [ thread-roots-task 298267820 298267835 ]
>  [ steal-task 298267836 298296403 ]
> GC-Thread 2 entries: 8
>  [ old-to-young-roots-task 298267585 298267715 ]
>  [ thread-roots-task 298267721 298267768 ]
>  [ thread-roots-task 298267769 298267783 ]
>  [ thread-roots-task 298267801 298267812 ]
>  [ thread-roots-task 298267814 298267819 ]
>  [ thread-roots-task 298267821 298267825 ]
>  [ scavenge-roots-task 298267826 298267924 ]
>  [ steal-task 298267925 298296466 ]
> GC-Thread 3 entries: 11
>  [ thread-roots-task 298267634 298267653 ]
>  [ thread-roots-task 298267659 298267680 ]
>  [ thread-roots-task 298267682 298267690 ]
>  [ thread-roots-task 298267692 298267725 ]
>  [ thread-roots-task 298267726 298267733 ]
>  [ thread-roots-task 298267735 298267741 ]
>  [ thread-roots-task 298267746 298267775 ]
>  [ thread-roots-task 298267776 298267787 ]
>  [ thread-roots-task 298267790 298267805 ]
>  [ thread-roots-task 298267807 298267813 ]
>  [ steal-task 298267848 298296340 ]
> GC-Thread 4 entries: 13
>  [ old-to-young-roots-task 298267561 298267611 ]
>  [ scavenge-roots-task 298267613 298267639 ]
>  [ thread-roots-task 298267640 298267661 ]
>  [ thread-roots-task 298267664 298267673 ]
>  [ thread-roots-task 298267675 298267685 ]
>  [ thread-roots-task 298267687 298267696 ]
>  [ thread-roots-task 298267699 298267707 ]
>  [ thread-roots-task 298267708 298267717 ]
>  [ thread-roots-task 298267725 298267765 ]
>  [ thread-roots-task 298267767 298267781 ]
>  [ thread-roots-task 298267807 298267828 ]
>  [ scavenge-roots-task 298267829 298267831 ]
>  [ steal-task 298267833 298296387 ]
> GC-Thread 5 entries: 13
>  [ old-to-young-roots-task 298267573 298267618 ]
>  [ thread-roots-task 298267622 298267651 ]
>  [ thread-roots-task 298267654 298267661 ]
>  [ thread-roots-task 298267663 298267669 ]
>  [ thread-roots-task 298267670 298267696 ]
>  [ thread-roots-task 298267698 298267704 ]
>  [ thread-roots-task 298267706 298267712 ]
>  [ thread-roots-task 298267719 298267726 ]
>  [ thread-roots-task 298267727 298267781 ]
>  [ thread-roots-task 298267784 298267791 ]
>  [ thread-roots-task 298267792 298267821 ]
>  [ scavenge-roots-task 298267823 298269583 ]
>  [ steal-task 298269584 298296338 ]
> GC-Thread 6 entries: 11
>  [ old-to-young-roots-task 298267551 298267601 ]
>  [ serial-old-to-young-roots-task 298267603 298267625 ]
>  [ thread-roots-task 298267626 298267653 ]
>  [ thread-roots-task 298267666 298267676 ]
>  [ thread-roots-task 298267678 298267684 ]
>  [ thread-roots-task 298267686 298267691 ]
>  [ thread-roots-task 298267692 298267723 ]
>  [ thread-roots-task 298267725 298267730 ]
>  [ thread-roots-task 298267789 298267803 ]
>  [ thread-roots-task 298267804 298267818 ]
>  [ steal-task 298267863 298296447 ]
> GC-Thread 7 entries: 8
>  [ old-to-young-roots-task 298267603 298267648 ]
>  [ thread-roots-task 298267650 298267687 ]
>  [ thread-roots-task 298267689 298267731 ]
>  [ thread-roots-task 298267773 298267786 ]
>  [ thread-roots-task 298267788 298267793 ]
>  [ thread-roots-task 298267797 298267855 ]
>  [ steal-task 298267857 298296336 ]
>  [ waitfor-barrier-task 298296341 298296578 ]
> GC-Thread 8 entries: 9
>  [ old-to-young-roots-task 298267594 298267634 ]
>  [ thread-roots-task 298267637 298267674 ]
>  [ thread-roots-task 298267675 298267712 ]
>  [ thread-roots-task 298267716 298267732 ]
>  [ thread-roots-task 298267760 298267768 ]
>  [ thread-roots-task 298267816 298267824 ]
>  [ scavenge-roots-task 298267826 298267828 ]
>  [ scavenge-roots-task 298267829 298267831 ]
>  [ steal-task 298267832 298296428 ]
> GC-Thread 9 entries: 17
>  [ old-to-young-roots-task 298267540 298267584 ]
>  [ old-to-young-roots-task 298267586 298267628 ]
>  [ thread-roots-task 298267629 298267652 ]
>  [ thread-roots-task 298267656 298267666 ]
>  [ thread-roots-task 298267667 298267676 ]
>  [ thread-roots-task 298267677 298267694 ]
>  [ thread-roots-task 298267698 298267708 ]
>  [ thread-roots-task 298267709 298267715 ]
>  [ thread-roots-task 298267744 298267754 ]
>  [ thread-roots-task 298267756 298267763 ]
>  [ thread-roots-task 298267765 298267775 ]
>  [ thread-roots-task 298267778 298267801 ]
>  [ thread-roots-task 298267802 298267809 ]
>  [ thread-roots-task 298267810 298267812 ]
>  [ thread-roots-task 298267817 298267823 ]
>  [ scavenge-roots-task 298267825 298267830 ]
>  [ steal-task 298267832 298296460 ]
> GC-Thread 10 entries: 12
>  [ scavenge-roots-task 298267613 298267618 ]
>  [ thread-roots-task 298267621 298267638 ]
>  [ thread-roots-task 298267639 298267659 ]
>  [ thread-roots-task 298267663 298267671 ]
>  [ thread-roots-task 298267673 298267682 ]
>  [ thread-roots-task 298267683 298267693 ]
>  [ thread-roots-task 298267695 298267705 ]
>  [ thread-roots-task 298267707 298267720 ]
>  [ thread-roots-task 298267723 298267730 ]
>  [ thread-roots-task 298267795 298267811 ]
>  [ thread-roots-task 298267813 298267833 ]
>  [ steal-task 298267834 298296472 ]
> GC-Thread 11 entries: 13
>  [ old-to-young-roots-task 298267514 298267589 ]
>  [ old-to-young-roots-task 298267592 298267657 ]
>  [ thread-roots-task 298267660 298267674 ]
>  [ thread-roots-task 298267677 298267693 ]
>  [ thread-roots-task 298267694 298267702 ]
>  [ thread-roots-task 298267706 298267716 ]
>  [ thread-roots-task 298267721 298267731 ]
>  [ thread-roots-task 298267735 298267744 ]
>  [ thread-roots-task 298267746 298267753 ]
>  [ thread-roots-task 298267757 298267786 ]
>  [ thread-roots-task 298267789 298267799 ]
>  [ thread-roots-task 298267802 298267814 ]
>  [ steal-task 298267838 298296336 ]
> GC-Thread 12 entries: 15
>  [ old-to-young-roots-task 298267499 298267597 ]
>  [ thread-roots-task 298267636 298267652 ]
>  [ thread-roots-task 298267654 298267686 ]
>  [ thread-roots-task 298267688 298267698 ]
>  [ thread-roots-task 298267701 298267710 ]
>  [ thread-roots-task 298267711 298267720 ]
>  [ thread-roots-task 298267723 298267730 ]
>  [ thread-roots-task 298267731 298267740 ]
>  [ thread-roots-task 298267743 298267755 ]
>  [ thread-roots-task 298267757 298267770 ]
>  [ thread-roots-task 298267772 298267783 ]
>  [ thread-roots-task 298267786 298267796 ]
>  [ thread-roots-task 298267798 298267805 ]
>  [ thread-roots-task 298267811 298267813 ]
>  [ steal-task 298267843 298296347 ]