The document discusses the history and features of garbage collection (GC) in Ruby. It notes that while GC has gotten a bad reputation for being slow or causing errors, it has actually been improved over time thanks to contributions from pioneering computer scientists. The document urges readers to see GC as an opportunity to strengthen their skills rather than a scapegoat for performance issues.

1. GC FAQ
nari/Narihiro Nakamura/
@nari_en
Network Applied Communication
Laboratory Ltd.
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2. Q: What do
you think
about REE?

3. A: Totally
awesome
approach!

4. But, REE
is based on
Ruby 1.8.7.

5. And, Ruby1.9's
GC has many
cool features.

6. Features of Ruby 1.9 series
✓ Suppression of Fragmentation -
since 1.9.1
✓ GC::Profiler - since 1.9.1
✓ LazySweepGC - since 1.9.3
✓ GC tuning params - since 1.9.3
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7. GC tuning
params

8. GC tuning params
✓ You can tune GC by using
environment variables.
✓ RUBY_GC_MALLOC_LIMIT
✓ RUBY_HEAP_MIN_SLOTS
✓ RUBY_FREE_MIN
✓ Since Ruby 1.9.3
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9. GC tuning params
✓ It's originally and idea from REE.
✓ <URL:http://
www.rubyenterpriseedition.com/
documentation.html#_garbage_collector
_performance_tuning>
✓ Please check this page if you are
interesting.
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10. BTW, REE
adopts the
Bitmap
Marking GC.

11. REE's Bitmap Marking
✓ It's implemented on Ruby 1.8's
heap structure.
✓ To port it for Ruby 1.9 would be
hard.
✓ And, it would be slow.
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12. I want to
create a faster
Bitmap
Marking GC.

13. For Ruby
1.9.4 or
later.

14. Q: What do
think about the
future of
CRuby's GC?

15. A: We need to
break
compatibility with
CRuby's C
extension.

16. We need efficient GC
algorithms
✓ Generational GC
✓ Incremental GC
✓ Concurrent GC
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17. But...
No pain,
No gain

18. Pains
✓ These algorithms need a write
barrier.
✓ We should insert a write barrier
on the C extension.
✓ This breaks compatibility of the C
extension.
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19. I'll create
some tools for
the transition.

20. I'm still
thinking about
how to do it.

21. Q: Why do
you like
GC?

22. A: I'm
not sure...

23. Paul
Graham
says

24. "Beating the
Averages"
http://www.flickr.com/photos/ringai/2733018174/

25. But, I
believe

26. "Beaten by the
Averages"
http://www.flickr.com/photos/ringai/2733018174/

27. For
example,
GC!!

28. GC is good
scapegoat.

29. e.g.
✓ "Memory isn't freed!"
✓ "The cause is GC!"
✓ "My program is slow!"
✓ "The cause is GC!"
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30. e.g.
✓ "SEGV!!"
✓ "GC!"
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31. GC is
always
picked on.

32. In
RubyKaigi2010,
Chad Fowler
says

33. "You're not Garbage
Collector"

34. GC is
always
picked on :P

35. But, GC was
made by really
cool hackers.

36. For
example,

37. John McCarthy
http://www.flickr.com/photos/null0/272015955/

38. He created the
Mark & Sweep
algorithm on
Lisp.

39. Marvin L. Minsky
taken by Bcjordan : http://en.wikipedia.org/wiki/File:Marvin_Minsky_at_OLPCb.jpg

40. He created the
Copying GC
algorithm.

41. Edsger Wybe
Dijkstra
photo 息2002 Hamilton Richards : http://userweb.cs.utexas.edu/users/EWD/

42. He created
Tri-color
marking.

43. Donald Ervin
Knuth
Flickr user Jacob Appelbaum : http://flickr.com/photos/ioerror/56359970/in/set-1220741/

44. He created
Lisp2(one of
Mark Compact
algorithms).

45. And many
other hackers
have studied
GC.

46. That means
GC is the
training school
of Hackers!

47. I think..

48. Become stronger by being beaten!

49. Let's become
stronger by being
beat together
with GC.

50. The
goal is ...

51. Punch-drunken
master!

52. Let's train
in GC
since now!!