Tuning Ruby's GC

A recipe for tuning MRI's GC, plus a shallow tour of how allocation and collection works.

Transcript

1. Tuning Ruby’s GC A recipe 1 Wednesday, August 21, 13
2. Deploy of Doom 2 Wednesday, August 21, 13
3. Performance hog No documentation Tons of blogs Black magic Ruby’s GC 3 Wednesday, August 21, 13
4. 37 Signals (REE) GC_MALLOC_LIMIT 59,000,000 HEAP_MIN_SLOTS 600,000 FREE_MIN 100,000 (Years ago) 4 Wednesday, August 21, 13
5. Twitter (Ruby 1.8.6) GC_MALLOC_LIMIT 50,000,000 HEAP_MIN_SLOTS 500,000 HEAP_SLOTS_ GROWTH_FACTOR 1 HEAP_SLOTS_INCREMENT 250,000 (April 2009) 5 Wednesday, August 21, 13
6. Not very satisfying... Let’s be methodical And automate it! 6 Wednesday, August 21, 13
7. Ruby Objects Immediates: Symbol, Fixnum, true, false, nil Everything else: pointer to RObject flags klass ...data... ...data... ...data... 7 Wednesday, August 21, 13
8. Ruby Objects Immediates: Symbol, Fixnum, true, false, nil Everything else: pointer to RObject flags klass len ptr capacity ...buffer... 7 Wednesday, August 21, 13
9. $ ruby X heaps Yi object slots 8 Wednesday, August 21, 13
10. $ ruby X heaps Yi object slots freelist 8 Wednesday, August 21, 13
11. Allocation def allocate if freelist empty run gc if freelist still empty allocate new heap object = freelist.pop # may malloc() set_up_object(object) object 9 Wednesday, August 21, 13
12. Collection def gc for each root mark(root) sweep() def mark(object) if object not yet marked mark object object.mark() def sweep for each heap for each object in heap if object not marked add object to freelist object.free() 10 Wednesday, August 21, 13
13. Adaptation next_heaps_length = heaps_used * initial_growth_factor malloc_limit += (inc - malloc_limit) * num_live_objects / num_objects free_min = heaps_used * HEAP_OBJ_LIMIT * 0.2 11 Wednesday, August 21, 13
14. Tuning Knobs GC_MALLOC_LIMIT 8,000,000 HEAP_MIN_SLOTS 10,000 FREE_MIN 4,096 HEAP_SLOTS_ GROWTH_FACTOR 1.8 12 Wednesday, August 21, 13
15. Your App GC_MALLOC_LIMIT ? HEAP_MIN_SLOTS ? FREE_MIN ? HEAP_SLOTS_ GROWTH_FACTOR ? 13 Wednesday, August 21, 13
16. Where do we want to be? 14 Wednesday, August 21, 13
17. Where do we want to be? 14 Wednesday, August 21, 13
18. gdb `which ruby` PID (gdb) p ruby_current_vm->objspace->malloc_params $1 = {limit = 60609413, increase = 9542176} (gdb) p ruby_current_vm->objspace->heap $2 = {increment = 0, ptr = 0x14b325f0, sweep_slots = 0x0, sorted = 0x15686ac0, length = 8377, used = 8291, freelist = 0x9f45138, range = {0xa48c10, 0x1a997978}, freed = 0x0, live_num = 733492, free_num = 2642474, free_min = 678203, final_num = 0, do_heap_free = 2204162} 15 Wednesday, August 21, 13
19. gdb `which ruby` PID (gdb) p ruby_current_vm->objspace->malloc_params $1 = {limit = 60609413, increase = 9542176} (gdb) p ruby_current_vm->objspace->heap $2 = {increment = 0, ptr = 0x14b325f0, sweep_slots = 0x0, sorted = 0x15686ac0, length = 8377, used = 8291, freelist = 0x9f45138, range = {0xa48c10, 0x1a997978}, freed = 0x0, live_num = 733492, free_num = 2642474, free_min = 678203, final_num = 0, do_heap_free = 2204162} HEAP_MIN_SLOTS = heap.length * 16384 / 40 15 Wednesday, August 21, 13
20. HowAboutWe (ruby 1.9.2) GC_MALLOC_LIMIT 59,000,000 HEAP_MIN_SLOTS 3,125,000 FREE_MIN 565,000 (August 2012) 16 Wednesday, August 21, 13
21. Better! 17 Wednesday, August 21, 13
22. GC::Profiler.enable COW-friendliness Lazy sweep GC 2.0 18 Wednesday, August 21, 13
23. Thanks! George Ogata @gogata oggy george.ogata@gmail.com Slides: http://speakerdeck.com/oggy/tuning-rubys-gc HowAboutWe We’re Hiring! 19 Wednesday, August 21, 13