From: "byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date: 2025-04-02T18:09:17+00:00
Subject: [ruby-core:121524] [Ruby Bug#21214] VmRSS consumption increase in Ruby 3.4.2 vs Ruby 3.3.6

Issue #21214 has been updated by byroot (Jean Boussier).


`ObjectSpace.memsize_of_all` being mostly stable suggest the difference is likely in the GC releasing the memory less eagerly, or having trouble releasing it because it's more fragmented.

>  any lead to reduce this peak?

There are a number of GC parameters you can tweak to make it more or less aggressive in reducing memory usage. Self-plug but [this post](https://shopify.engineering/adventures-in-garbage-collection#) is the most up to date  writup on GC tuning. It's goal are quite contrary to yours, but it explains what the key settings do, so it could be helpful to you.

You can also try calling `GC.compact` in between workloads to reduce fragmentation.

----------------------------------------
Bug #21214: VmRSS consumption increase in Ruby 3.4.2 vs Ruby 3.3.6
https://bugs.ruby-lang.org/issues/21214#change-112550

* Author: mood_vuadensl (LOIC VUADENS)
* Status: Open
* ruby -v: ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-linux]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Hello,

After updating Ruby from 3.3.6 to 3.4.2, our batch-style (not based on rails) application exceed its memory limit.
Below is an example script that runs on both versions and demonstrates that 'ObjectSpace.memsize_of_all' does not vary significantly, but the OS 'VmRSS' increases significantly.

Do you have any information on what might have caused this increase or any lead to reduce this peak?

Here is the result on a Linux 5.15.167.4-microsoft-standard-WSL2:
with Ruby 3.3.6:
```text
ruby 3.3.6 (2024-11-05 revision 75015d4c1f) [x86_64-linux]
On start on 3.3.6
- OS VmRSS:        20616 kB
- ObjectSpace.memsize_of_all: 1.7MB

 On first full workload: 0
- OS VmRSS:       559212 kB
- ObjectSpace.memsize_of_all: 327.86MB

....
After workload
- OS VmRSS:       711776 kB
- ObjectSpace.memsize_of_all: 327.86MB

After data released
- OS VmRSS:       616364 kB
- ObjectSpace.memsize_of_all: 1.71MB
```
and 3.4.2:
```text
ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-linux]
On start on 3.4.2
- OS VmRSS:        13076 kB
- ObjectSpace.memsize_of_all: 1.7MB

 On first full workload: 0
- OS VmRSS:       674324 kB
- ObjectSpace.memsize_of_all: 353.6MB

....
After workload
- OS VmRSS:      1000628 kB
- ObjectSpace.memsize_of_all: 327.85MB

After data released
- OS VmRSS:       843636 kB
- ObjectSpace.memsize_of_all: 1.7MB
```

and the associated script:
```ruby
require 'objspace'

BYTES_TO_MB = 1024 * 1024

$stdout.sync = true
srand(1)

# Declare supporting code
def print_info(context)
  puts context
  GC.start

  os_mem_metric = File.readlines("/proc/#{Process.pid}/status").find { |line| line.start_with?('VmRSS:') }
  puts "- OS #{os_mem_metric}"
  puts "- ObjectSpace.memsize_of_all: #{(ObjectSpace.memsize_of_all.to_f/BYTES_TO_MB).round(2)}MB"
  puts ''
end

def random_string = Array.new(10) { rand(99) }.join

class A
  def initialize
    @a = random_string
    @b = rand(1000000000000)
  end
end


# Main
print_info "On start on #{RUBY_VERSION}"

objects = Array.new(1_000_000) { A.new }
hashes =  Array.new(250_000) { { a: rand(100_000), b: rand(100_000), c: random_string } }
arrays =  Array.new(250_000) { [rand(100_000), rand(100_000), random_string] }

keep_if = ->(index) { index.even? }
0.upto(3) do |i_loop|
  objects = objects.map.with_index { |obj, index| keep_if.call(index) ? obj : A.new }
  hashes = hashes.map.with_index { |obj, index| keep_if.call(index) ? obj : { a: rand(10_000), b: rand(10_000), c: random_string } }
  arrays = arrays.map.with_index { |obj, index| keep_if.call(index) ? obj : [rand(10_000), rand(10_000), random_string] }

  print_info " On first full workload: #{i_loop}" if i_loop.zero?

  keep_if = ->(index) { index.odd? } if i_loop == 1
  keep_if = ->(index) { index%5 == 0 } if i_loop == 2
  keep_if = ->(index) { index.even? } if i_loop == 3
  print '.'
end
puts ''

print_info 'After workload'

objects.clear
hashes.clear
arrays.clear

print_info 'After data released'
```

Regards




-- 
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