[ruby-core:121452] [Ruby Bug#21201] Performance regression when defining methods inside `refine` blocks

Issue #21201 has been updated by byroot (Jean Boussier).


>  I was wondering if there might be any ideas to make it faster, or to handle the invalidation more efficiently.

The solution is likely to keep the list (set) of all existing call caches that belong to a refinement, as to save the object space traversal.

But yes, this performance issue is why at work we disallowed usage of refinement using rubocop.

----------------------------------------
Bug #21201: Performance regression when defining methods inside `refine` blocks
https://bugs.ruby-lang.org/issues/21201#change-112451

* Author: alpaca-tc (Hiroyuki Ishii)
* Status: Open
* ruby -v: 3.3.7, 3.4.2, 3.5.0
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
After the change introduced in [PR #10037](https://github.com/ruby/ruby/pull/10037), a significant performance regression has been observed when defining methods within refine blocks.

The PR correctly fixes a bug where `callcache` invalidation was missing when methods are defined inside a refinement. To fix this, it now invokes [`rb_clear_all_refinement_method_cache()`](https://github.com/ruby/ruby/blob/752a1d785475d1950b33c7d77b289a6a3a753f02/vm_method.c#L439-L443) at the time of method definition within `refine`. However, this function performs a full object space traversal via `rb_objspace_each_objects`, making it extremely expensive.

In our team's Rails application, refinements are used heavily. During application code reload (triggered in development mode), `rb_clear_all_refinement_method_cache()` is called 1425 times, 1142 of which originate via `rb_clear_method_cache()`. As a result, the code reload time has increased from **5 seconds** to **15 seconds** after the patch. Since reloading occurs every time the code changes, this degrades development experience severely.

### Reproduction script:
```ruby
require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  gem "benchmark-ips"
end

mod = Module.new
klass = Class.new

Benchmark.ips do |x|
  x.report(RUBY_VERSION) do
    mod.send(:refine, klass) do
      def call_1 = nil
      def call_2 = nil
      def call_3 = nil
    end
  end

  x.save! "/tmp/performance_regression_refine.bench"
  x.compare!
end
```

### Benchmark results:
```
Comparison:
               3.2.7:  1500316.7 i/s
               3.3.7:      158.0 i/s - 9496.46x  slower
               3.5.0:      124.6 i/s - 12041.43x  slower
               3.4.2:      119.5 i/s - 12553.50x  slower
```

Related Slack discussion: https://ruby-jp.slack.com/archives/CLWSHA76V/p1741932018811539  
I totally understand the necessity and value of the past PR that fixed the callcache bugs. That said, I was wondering if there might be any ideas to make it faster, or to handle the invalidation more efficiently.



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