From: "hsbt (Hiroshi SHIBATA) via ruby-core" <ruby-core@...>
Date: 2023-11-20T02:51:27+00:00
Subject: [ruby-core:115423] [Ruby master Bug#19969] Regression of memory usage with Ruby 3.1

Issue #19969 has been updated by hsbt (Hiroshi SHIBATA).


Thanks nobu and nagachika.

I confirmed to resolve this regrassion with `ruby_3_2` branch.

```
# Before
$ ruby -v -rset -e 's1 = Set.new(10000.times); s2 = Set.new(9999.times); Array.new(10000) { s1 - s2 - [0] }; puts `ps -o rss= -p #{$$}`.to_i'
ruby 3.2.2 (2023-07-05 revision 2f603bc4d7) +YJIT [arm64-darwin23]
4564304

# After
$ ruby -v -rset -e 's1 = Set.new(10000.times); s2 = Set.new(9999.times); Array.new(10000) { s1 - s2 - [0] }; puts `ps -o rss= -p #{$$}`.to_i'
ruby 3.2.2 (2023-11-19 revision d9f4f321c6) +YJIT [arm64-darwin23]
40864
```


----------------------------------------
Bug #19969: Regression of memory usage with Ruby 3.1
https://bugs.ruby-lang.org/issues/19969#change-105354

* Author: hsbt (Hiroshi SHIBATA)
* Status: Closed
* Priority: Normal
* Backport: 3.0: DONTNEED, 3.1: REQUIRED, 3.2: DONE
----------------------------------------
Our company that is ANDPAD, Inc. encountered to increase memory usage after upgrading Ruby 3.2 from 3.0 on our Rails application. This increase size is about 20%.

My colleague found this [root cause](https://bugs.ruby-lang.org/issues/16996) and reproduction code:

```
$ ruby -v -rset -e 's1 = Set.new(10000.times); s2 = Set.new(9999.times); Array.new(10000) { s1 - s2 - [0] }; puts `ps -o rss= -p #{$$}`.to_i'
ruby 3.0.6p216 (2023-06-29 revision bdfe1958a8) +JIT [arm64-darwin22]
248096

$ ruby -v -rset -e 's1 = Set.new(10000.times); s2 = Set.new(9999.times); Array.new(10000) { s1 - s2 - [0] }; puts `ps -o rss= -p #{$$}`.to_i'
ruby 3.2.2 (2023-07-05 revision 2f603bc4d7) +YJIT [arm64-darwin22]
2949280
```

Should we revert #16996 for Ruby 3.1 or later? I'm not sure this increased memory usage is reasonable with performance improvement.





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