Use Puma `nakayoshi_fork`

https://github.com/puma/puma/blob/master/5.0-Upgrade.md#nakayoshi_fork
Enabled by default. ENV var for better control.

config/puma.example.development.rb

@@ -80,9 +80,10 @@ tag 'gitlab-puma-worker'
 worker_timeout 60
 
 # https://github.com/puma/puma/blob/master/5.0-Upgrade.md#lower-latency-better-throughput
-if defined?(wait_for_less_busy_worker)
-  wait_for_less_busy_worker ENV.fetch('PUMA_WAIT_FOR_LESS_BUSY_WORKER', 0.001).to_f
-end
+wait_for_less_busy_worker ENV.fetch('PUMA_WAIT_FOR_LESS_BUSY_WORKER', 0.001).to_f
+
+# https://github.com/puma/puma/blob/master/5.0-Upgrade.md#nakayoshi_fork
+nakayoshi_fork ActiveModel::Type::Boolean.new.cast(ENV.fetch('PUMA_NAKAYOSHI_FORK_ENABLED', true))
 
 # Use json formatter
 require_relative "/home/git/gitlab/lib/gitlab/puma_logging/json_formatter"

config/puma.rb.example

@@ -70,9 +70,10 @@ tag 'gitlab-puma-worker'
 worker_timeout 60
 
 # https://github.com/puma/puma/blob/master/5.0-Upgrade.md#lower-latency-better-throughput
-if defined?(wait_for_less_busy_worker)
-  wait_for_less_busy_worker ENV.fetch('PUMA_WAIT_FOR_LESS_BUSY_WORKER', 0.001).to_f
-end
+wait_for_less_busy_worker ENV.fetch('PUMA_WAIT_FOR_LESS_BUSY_WORKER', 0.001).to_f
+
+# https://github.com/puma/puma/blob/master/5.0-Upgrade.md#nakayoshi_fork
+nakayoshi_fork ActiveModel::Type::Boolean.new.cast(ENV.fetch('PUMA_NAKAYOSHI_FORK_ENABLED', true))
 
 # Use json formatter
 require_relative "/home/git/gitlab/lib/gitlab/puma_logging/json_formatter"

config/puma_actioncable.example.development.rb

@@ -80,9 +80,10 @@ tag 'gitlab-actioncable-puma-worker'
 worker_timeout 60
 
 # https://github.com/puma/puma/blob/master/5.0-Upgrade.md#lower-latency-better-throughput
-if defined?(wait_for_less_busy_worker)
-  wait_for_less_busy_worker ENV.fetch('PUMA_WAIT_FOR_LESS_BUSY_WORKER', 0.001).to_f
-end
+wait_for_less_busy_worker ENV.fetch('PUMA_WAIT_FOR_LESS_BUSY_WORKER', 0.001).to_f
+
+# https://github.com/puma/puma/blob/master/5.0-Upgrade.md#nakayoshi_fork
+nakayoshi_fork ActiveModel::Type::Boolean.new.cast(ENV.fetch('PUMA_NAKAYOSHI_FORK_ENABLED', true))
 
 # Use json formatter
 require_relative "/home/git/gitlab/lib/gitlab/puma_logging/json_formatter"