Avoid taking vm barrier in heap_prepare() #14425
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gc/default/default.c
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| bool needs_gc = is_incremental_marking(objspace) || (heap->free_pages == NULL && is_lazy_sweeping(objspace)); | ||
| if (needs_gc) { | ||
| gc_enter(objspace, gc_enter_event_continue, &lock_lev); // takes vm barrier, try to avoid | ||
| } |
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What about an early return instead?
Suggested change
| bool needs_gc = is_incremental_marking(objspace) || (heap->free_pages == NULL && is_lazy_sweeping(objspace)); | |
| if (needs_gc) { | |
| gc_enter(objspace, gc_enter_event_continue, &lock_lev); // takes vm barrier, try to avoid | |
| } | |
| bool needs_gc = is_incremental_marking(objspace) || (heap->free_pages == NULL && is_lazy_sweeping(objspace)); | |
| if (!needs_gc) { | |
| return; | |
| } |
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nobu
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Sep 14, 2025
gc/default/default.c
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| { | ||
| unsigned int lock_lev; | ||
| gc_enter(objspace, gc_enter_event_continue, &lock_lev); | ||
| bool needs_gc = is_incremental_marking(objspace) || (heap->free_pages == NULL && is_lazy_sweeping(objspace)); |
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How about extracting a macro:
/* In lazy sweeping or the previous incremental marking finished and
* did not yield a free page. */
#define needs_continue_sweeping(objspace, heap) \
((heap)->free_pages == NULL && is_lazy_sweeping(objspace))
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We can avoid taking this barrier if we're not incremental marking or lazy sweeping. I found this was taking a significant amount of samples when profiling `Psych.load` in multiple ractors due to the vm barrier. With this change, we get significant improvements in ractor benchmarks that allocate lots of objects. -- Psych.load benchmark -- ``` Before: After: r: itr: time r: itr: time 0 ruby#1: 960ms 0 ruby#1: 943ms 0 ruby#2: 979ms 0 ruby#2: 939ms 0 ruby#3: 968ms 0 ruby#3: 948ms 0 ruby#4: 963ms 0 ruby#4: 946ms 0 ruby#5: 964ms 0 ruby#5: 944ms 1 ruby#1: 947ms 1 ruby#1: 940ms 1 ruby#2: 950ms 1 ruby#2: 947ms 1 ruby#3: 962ms 1 ruby#3: 950ms 1 ruby#4: 947ms 1 ruby#4: 945ms 1 ruby#5: 947ms 1 ruby#5: 943ms 2 ruby#1: 1131ms 2 ruby#1: 1005ms 2 ruby#2: 1153ms 2 ruby#2: 996ms 2 ruby#3: 1155ms 2 ruby#3: 1003ms 2 ruby#4: 1205ms 2 ruby#4: 1012ms 2 ruby#5: 1179ms 2 ruby#5: 1012ms 4 ruby#1: 1555ms 4 ruby#1: 1209ms 4 ruby#2: 1509ms 4 ruby#2: 1244ms 4 ruby#3: 1529ms 4 ruby#3: 1254ms 4 ruby#4: 1512ms 4 ruby#4: 1267ms 4 ruby#5: 1513ms 4 ruby#5: 1245ms 6 ruby#1: 2122ms 6 ruby#1: 1584ms 6 ruby#2: 2080ms 6 ruby#2: 1532ms 6 ruby#3: 2079ms 6 ruby#3: 1476ms 6 ruby#4: 2021ms 6 ruby#4: 1463ms 6 ruby#5: 1999ms 6 ruby#5: 1461ms 8 ruby#1: 2741ms 8 ruby#1: 1630ms 8 ruby#2: 2711ms 8 ruby#2: 1632ms 8 ruby#3: 2688ms 8 ruby#3: 1654ms 8 ruby#4: 2641ms 8 ruby#4: 1684ms 8 ruby#5: 2656ms 8 ruby#5: 1752ms ```
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Nov 3, 2025
* master: (381 commits) ZJIT: Implement include_p for opt_(new|dup)array_send YARV insns (ruby#14885) Avoid taking vm barrier in heap_prepare() (ruby#14425) [ruby/json] ext/json/ext/json.h: Add missing newline at end of file [ruby/json] Fix duplicate 'inline' declaration specifier [ruby/json] Fix check_dependency [ruby/json] parser.c: Always inline `json_eat_whitespace` [ruby/json] parser.c: use `rb_str_to_interned_str` over `rb_funcall` [ruby/json] parser.c: Extract `json_string_cacheable_p` [ruby/json] parser.c: simplify sorted insert loop in rstring_cache_fetch [ruby/json] parser.c: Skip checking for escape sequences in `rstring_cache_fetch` [ruby/json] Centralize macro definitions [DOC] Tweaks for String#to_f pend on Windows for timeouts Fix incorrect RUBY_DEBUG range Make Namespace.root visible not only for debugging Use CFUNC namespace only for IFUNC frames, its behavior should be unchanged Fix use of inappropriate debug flag Add flag to ignore EXPERIMENTAL warnings No need to call rb_define_class/module_under_id Add basic namespace tests ...
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We can avoid taking this barrier if we're not incremental marking or lazy sweeping. I found this was taking a significant amount of samples when profiling
Psych.loadin multiple ractors due to the vm barrier. With this change, we get significant improvements in ractor benchmarks that allocate lots of objects.-- Psych.load benchmark --