Bug #9201: [patch] remove GC overhead for loaded_features_index

• Status: Closed
• Assignee: nobu (Nobuyoshi Nakada)
• Target version: 2.1.0
• ruby -v: ruby 2.1.0dev (2013-12-02 trunk 43955)
• Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN

[tmm1 (Aman Karmani)]

I was profiling minor GC in our app and noticed 15% of time spent in mark_tbl for loaded_features_index.

The following patch removes this overhead by storing feature offsets outside the ruby heap:

https://github.com/tmm1/ruby/commit/d03c5ece865422f0510957c1dee1d33a1d9eca82

[tmm1 (Aman Karmani)]

In features_index_add_single, we already Check_Type(offset, T_FIXNUM). This ensures these off-heap RArrays will only contain immediates and do not need to be marked.

[tmm1 (Aman Karmani)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r43974.
Aman, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• load.c (features_index_add_single): Move loaded_features_index array values off
  the ruby heap. [Bug #9201] [ruby-core:58805]
• load.c (loaded_features_index_clear_i): Clean up off-heap array structure.
• vm.c (rb_vm_mark): Remove unnecessary mark_tbl for loaded_features_index.
  This improves minor GC time by 15% in a large application.

[tmm1 (Aman Karmani)]

With this patch along with the one in r43973, minor GC pauses are now up to 45% shorter in our application.

10.times{ s=Time.now; GC.start_minor; p Time.now-s }

r43972

0.034701
0.034337
0.038741
0.034126
0.037504
0.033009
0.034526
0.033238
0.034232
0.032667

r43973

0.029089
0.027402
0.027296
0.026581
0.028211
0.026294
0.028213
0.030031
0.026412
0.02695

r43974

0.024061
0.021339
0.022207
0.022007
0.022716
0.02303
0.022139
0.021704
0.022118
0.021611

[funny_falcon (Yura Sokolov)]

Look at #8158 . Don't know if it still applies, but I will fix it if you interested in.