Server Memory - Chernivtsi JS 2019

Transcript

1. None

2. @listochkin fb.com/tektonna

3. Not a JavaScript talk

4. No CSS No frameworks No Node

5. A bit deeper than most talks on similar subject

6. None

7. How programming languages work

8. Just-in-time compilers Garbage Collection

9. Memory Management

10. Server runs our programs

11. CPU Caches RAM Swap Disk Network

12. Operating System

13. None

14. Pages

15. 4k

16. Virtual

17. 2 processes [0 … ∞]

18. Oh, I got a pointer at 4096 What’s at 4095?

19. Page fault

20. Allocate page But not really

21. Once you start writing to it

22. not 4k?

23. None
24. None

25. malloc

26. None

27. malloc me some memory

28. a pointer

29. free(pointer)

30. malloc malloc malloc free malloc free free

31. Forget to free Free the wrong pointer Read from unallocated

    memory

32. Can we do better?

33. Reference Counting

34. None

35. const players = [ … ] players.forEach(p => makeMove(p))

36. a = … doX(a) yield a

37. scope

38. if ( … ) { let a = … …

    }
39. None

40. C++: std::shared_ptr

41. None

42. Optimizations

43. Delayed Counting

44. Don’t count local references

45. function (user) { let email = user.email; … … }

46. Delayed deallocation

47. Cycle Collector

48. None
49. None

50. Compile time ref-counting

51. Several types of pointers

52. Ownership

53. Forbids cycles by forbidding several owning references at the same

    time
54. None
55. None
56. None

57. Perl 1987 - today Python 1991 - 2001 PHP 1994

    - 2009

58. Multiprocess deploys

59. fork

60. Copy on Write

61. Worker Accepts requests As memory use raises: Stop accepting requests

    Complete in-flight requests Terminate

62. Master Keep track on workers Start new workers Signal them

    to terminate when memory pressure is high

63. “Pre-fork”

64. Load the framework Load app code Run full GC Start

    forking process to accept requests
65. None
66. None

67. “Processes”

68. Tracing GC

69. 1959 60 years ago

70. Start at Root references Follow all references Build a live

    objects tree Delete all objects not part of the tree

71. Ruby Java JavaScript Lua Go

72. Roots?

73. Constants Global variables Local variables Closures Thread-locals ...

74. Mark & Sweep vs Mark-Compact

75. None

76. Can you move objects after mark?

77. Team Sweep: Go Ruby* Lua Embedded JS engines Erlang

78. Pros: Pointers don’t change Native extensions Easier to implement

79. Team Compact: Java JavaScript Ruby* Haskell

80. Pros: Less memory fragmentation over time Cons: Harder Takes longer

    to do a GC

81. Mark all memory

82. None

83. Incremental Marking

84. 3-colored algorithm by Dijkstra™

85. None
86. None
87. None
88. None
89. None

90. What is a barrier? if statement

91. else branch is very rare CPU branch predictor

92. Parallel marking

93. None
94. None

95. Lazy Sweep

96. Generational

97. Temporary data

98. Major vs Minor GC

99. Pointers from Old objects to new objects

100. Remembered Set

101. Major GC Scan roots only Bigger object graph

102. Minor GC Scan roots + RS Small object graph

103. None

104. Modern GCs are hybrid

105. None
106. None

107. C-extensions

108. Can’t move objects if their references are passed to an

     extension

109. Can’t add WB

110. RGen GC

111. 2 types of objects WB-protected WB-unprotected

112. WBu are never OldGen

113. OldGen -> WBu WBu to Remembered Set

114. Mark WBus on every minor GC

115. 1 stw to mark all WBu in RS

116. None
117. None

118. Adding compaction for WBp

119. None

120. V8

121. Minor GC Parallel

122. Major Parallel marking Parallel / Concurrent Compact || Sweep

123. None

124. When to trigger GC?

125. Out-of-Bounds GC

126. request? Minor GCs response is sent? Major GC

127. Firefox Run GC in background tabs first instead of current

     tab

128. Chrome Animation frame

129. Walking the memory

130. Cache locality

131. GPU

132. OS Pages pre-forked processes malloc zones GC Pages Remembered Sets

     Barriers
133. None
134. None