From: marcandre-ruby-core@...
Date: 2020-07-15T16:11:41+00:00
Subject: [ruby-core:99180] [Ruby master Bug#17031] `Kernel#caller_locations(m, n)` should be optimized

Issue #17031 has been updated by marcandre (Marc-Andre Lafortune).


Sure

```
Calculating -------------------------------------
     short_backtrace     28.315k (� 7.1%) i/s -    141.984k in   5.044733s
      long_backtrace     24.168k (� 8.7%) i/s -    120.900k in   5.050243s
 no_caller_locations     29.288k (� 2.5%) i/s -    148.359k in   5.068723s
Total allocated: 1.58 kB (3 objects)
Total retained:  0 B (0 objects)

Total allocated: 19.58 kB (3 objects)
Total retained:  0 B (0 objects)
```

I got a factor 6.2 this time: (1/24.168-1/29.288)/(1/28.315-1/29.288)
 
 


----------------------------------------
Bug #17031: `Kernel#caller_locations(m, n)` should be optimized
https://bugs.ruby-lang.org/issues/17031#change-86559

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
`Kernel#caller_locations(1, 1)` currently appears to needlessly allocate memory for the whole backtrace.

It allocates ~20kB for a 800-deep stacktrace, vs 1.6 kB for a shallow backtrace.
It is also much slower for long stacktraces: about 7x slower for a 800-deep backtrace than for a shallow one.

Test used:
```ruby
def do_something
  location = caller_locations(1, 1).first
end

def test(depth, trigger)
  do_something if depth == trigger

  test(depth - 1, trigger) unless depth == 0
end

require 'benchmark/ips'

Benchmark.ips do |x|
  x.report (:short_backtrace    )    {test(800,800)}
  x.report (:long_backtrace     )    {test(800,  0)}
  x.report (:no_caller_locations)    {test(800, -1)}
end

require 'memory_profiler'

MemoryProfiler.report { test(800,800) }.pretty_print(scale_bytes: true, detailed_report: false)
MemoryProfiler.report { test(800,  0) }.pretty_print(scale_bytes: true, detailed_report: false)
```

Found when checking memory usage on RuboCop.




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