[ruby-core:121153] [Ruby master Misc#20652] Memory allocation for gsub has increased from Ruby 2.7 to 3.3
From:
"byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date:
2025-02-24 17:35:21 UTC
List:
ruby-core #121153
Issue #20652 has been updated by byroot (Jean Boussier).
Sorry, I wasn't clear. The allocation is eluded if the previous MatchData wasn't accessed. If it was, I'm afraid there's nothing we can safely do.
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Misc #20652: Memory allocation for gsub has increased from Ruby 2.7 to 3.3
https://bugs.ruby-lang.org/issues/20652#change-112090
* Author: orisano (Nao Yonashiro)
* Status: Closed
* Assignee: jeremyevans0 (Jeremy Evans)
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I recently upgraded from ruby 2.7.7 to 3.3.1 and noticed that the GC load increased.
When I used the allocation profiler to investigate, I found that memory allocation from gsub had increased.
The problem was code like this:
```ruby
s = "foo "
s.gsub(/ (\s+)/) { " #{' ' * Regexp.last_match(1).length}" }
```
When I compared the results of heap-profiler between 2.7.7 and 3.3.1, I found that MatchData was increasing.
https://gist.github.com/orisano/98792dee260106e9b6fcb45bbabeb1e6
https://github.com/ruby/ruby/commit/abc0304cb28cb9dcc3476993bc487884c139fd11
I discovered that the cause is this commit, which stopped reusing backref to avoid race conditions.
Is there a way to reuse backref while still avoiding race conditions?
--
https://bugs.ruby-lang.org/
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