ESUG 2011, Edinburgh

1. VisualWorks Object
Memory Management
Andrés Valloud

2. Structure

3. Eden

4. SA
Eden
SB

5. SA
Eden
SB
Old

6. SA
Eden
SB
Old
Perm

7. Evolution

8. Instance
creation

9. Scavenge 1

10. Scavenge 2

11. Scavenge 3

12. Scavenge 4

13. Tenured

14. IGC / GC

15. Perm save

16. Global GC
R IP

17. But, speaking of GC...

18. SA
Eden
SB
Old
Perm

19. Scavenge finds
SA
live objects Eden
SB
faster
RT Old
Perm

20. Scavenge finds
SA
live objects Eden
SB
faster
RT Old
IGC / GC find
Old
live objects Perm
RT
faster

21. Responsibilities

22. SA
Eden
SB
RT Old
Old
Perm
RT

23. VM scavenges SA
Eden
new space SB
RT Old
Old
Perm
RT

24. VM scavenges SA VI must ensure
Eden
new space SB success
RT Old
Old
Perm
RT

25. VM scavenges SA VI must ensure
Eden
new space SB success
VM signals low
memory RT Old
semaphore
Old
Perm
RT

26. VM scavenges SA VI must ensure
Eden
new space SB success
VM signals low VI manages old
memory RT Old space (GC,
semaphore grow, shrink)
Old
Perm
RT

27. VM scavenges SA VI must ensure
Eden
new space SB success
VM signals low VI manages old
memory RT Old space (GC,
semaphore grow, shrink)
VM (few) Old VI memory
Perm policy classes
fixed actions RT

28. Memory policies

29. Worst case SA
Eden
scavenge SB
RT Old
Old
Perm
RT

30. Worst case SA Eden and
Eden
scavenge SB SA or SB full
RT Old
Old
Perm
RT

31. Worst case SA Eden and
Eden
scavenge SB SA or SB full
RT Old RT grows
Old
Perm
RT

32. Worst case SA Eden and
Eden
scavenge SB SA or SB full
RT Old RT grows
Old
Perm Old RT grows
RT

33. Worst case
SA Eden and
scavenge Eden
SB SA or SB full
due to GC
Stack RT Old RT grows
Stack zone full,
flushed to
object memory
Old
Perm Old RT grows
RT

34. The picture
Worst Case
Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

35. The picture
Growth Worst Case
Increments Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

36. Improvements since
VisualWorks 7.7

37. Fixed since VW 7.7
ObjectMemory>>igcState
...
aborting ifTrue: [^#aborting].
...
MemoryPolicy>>dealWithIGC
...
memoryStatus igcState = #aborted
ifTrue: [“recover from IGC abort”].
...

38. Fixed since VW 7.7
ObjectMemory>>igcState
...
aborting ifTrue: [^#aborting].
...
IGC does not
recover from
stack overflow
MemoryPolicy>>dealWithIGC
...
memoryStatus igcState = #aborted
ifTrue: [“recover from IGC abort”].
...

39. Fixed since VW 7.7
Worst Case
Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

40. Fixed since VW 7.7
IGC as last
resort, bogus
emergencies Worst Case
Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

41. Fixed since VW 7.7
VM crash due
to scavenge
failure Worst Case
Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

42. Fixed since VW 7.7
Too low for
modern
applications Worst Case
Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

43. Fixed since VW 7.7
Growth Worst Case
Increments Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

44. Fixed since VW 7.7
Tiny growth
increment,
excessive GC Worst Case
Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

45. Fixed since VW 7.7
Tiny growth
increment,
fragmentation Worst Case
Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

46. Fixed since VW 7.7
Low free
memory limit,
even more GC Worst Case
Scavenge
Upper
0 Memory
Bound
Growth
Image Emergency
Regime
Size Threshold
Bound

47. New technology

48. E S T S
New technology
T

49. E S T S
New technology
T
•MemoryPolicyChecker

50. E S T S
New technology
T
•MemoryPolicyChecker
•MemoryPolicyTuner

51. E S T S
New technology
T
•MemoryPolicyChecker
•MemoryPolicyTuner
•MemoryPolicyStressTest

53. Before and after

54. Before
Upper
0 Memory
Bound
Upper
0 Memory
Bound
After

55. Run time per stress test case, in seconds
40,000
30,000
20,000
10,000
0
A (x100) B (x100) C (x400) D (x40) E (x40) F (x6) G (x6)
VW 7.7 legacy MemoryPolicy (with fixes) ~1 day, if they work
VW 7.7.1 without sizesAtStartup tuning ~160 minutes
VW 7.7.1 default ~73 minutes
A: pointer garbage Segmented container Large container
B: byte garbage D: byte allocation F: byte allocation
C: point creation E: pointer allocation G: pointer allocation

56. Print 2 web, ESUG 2009

57. Print 2 web, ESUG 2009
X
2.5x faster
(with small
changes only)

58. VisualWorks 7.8
and beyond

59. VisualWorks 7.8+
•Fixed space allocation fixed
•Improved weak / ephemeron support
•IGC performance improvements
•GC / IGC mark stack overflow prevention
•GC moves large objects back into large space
•New -m[1..7] VM switches

60. VisualWorks 7.8+
•Fixed space allocation fixed
N E
•Improved weak / ephemeron support
O
D
•IGC performance improvements
•GC / IGC mark stack overflow prevention
•GC moves large objects back into large space
•New -m[1..7] VM switches

61. VisualWorks 7.9

62. VisualWorks 7.9
•Up to 40% faster GC

63. VisualWorks 7.9
•Up to 40% faster GC
•Improved IGC uses less memory

64. VisualWorks 7.9
•Up to 40% faster GC
•Improved IGC uses less memory
•Adaptive time based memory policy IGC driver

65. VisualWorks 7.9
•Up to 40% faster GC
•Improved IGC uses less memory
•Adaptive time based memory policy IGC driver
•Memory policy IGC smart abort

66. VisualWorks 7.9
•Up to 40% faster GC
•Improved IGC uses less memory
•Adaptive time based memory policy IGC driver
•Memory policy IGC smart abort
•Memory policy IGC switch

67. VisualWorks 7.9
•Up to 40% faster GC
•Improved IGC uses less memory
•Adaptive time based memory policy IGC driver
•Memory policy IGC smart abort
•Memory policy IGC switch
•Updates to the OldRT, become:, fixed space...

68. VisualWorks 7.9
•Up to 40% faster GC
O N E
•Improved IGC uses less memory
D
•Adaptive time based memory policy IGC driver
•Memory policy IGC smart abort
•Memory policy IGC switch
•Updates to the OldRT, become:, fixed space...

69. Questions?