From b2e8adf140e0c5cda56a51ec916ccda9938135be Mon Sep 17 00:00:00 2001
From: shields <shields@tablecheck.com>
Date: Sun, 9 Jan 2022 20:04:23 +0900
Subject: [PATCH 1/4] When using fork_worker mode, worker_culling_strategy
 "oldest" shouldn't cull worker 0.

---
 lib/puma/cluster.rb              | 21 ++++++++++++---------
 test/test_integration_cluster.rb | 19 +++++++++++++++++++
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/lib/puma/cluster.rb b/lib/puma/cluster.rb
index d90c81d569..749704aea0 100644
--- a/lib/puma/cluster.rb
+++ b/lib/puma/cluster.rb
@@ -109,15 +109,9 @@ def cull_workers
       diff = @workers.size - @options[:workers]
       return if diff < 1
 
-      debug "Culling #{diff.inspect} workers"
-
-      workers_to_cull =
-        case @options[:worker_culling_strategy]
-        when :youngest
-          @workers.sort_by(&:started_at)[-diff,diff]
-        when :oldest
-          @workers.sort_by(&:started_at)[0,diff]
-        end
+      debug "Culling #{diff} workers"
+
+      workers_to_cull = @workers.sort_by(&:started_at)[cull_start_index(diff), diff]
 
       debug "Workers to cull: #{workers_to_cull.inspect}"
 
@@ -127,6 +121,15 @@ def cull_workers
       end
     end
 
+    def cull_start_index(diff)
+      case @options[:worker_culling_strategy]
+      when :oldest
+        @options[:fork_worker] ? 1 : 0
+      else # :youngest
+        -diff
+      end
+    end
+
     # @!attribute [r] next_worker_index
     def next_worker_index
       occupied_positions = @workers.map(&:index)
diff --git a/test/test_integration_cluster.rb b/test/test_integration_cluster.rb
index aaccd38507..979765f067 100644
--- a/test/test_integration_cluster.rb
+++ b/test/test_integration_cluster.rb
@@ -401,6 +401,25 @@ def test_culling_strategy_oldest
     assert_match(/Worker 0 \(PID: \d+\) terminating/, line)
   end
 
+  def test_culling_strategy_oldest_fork_worker
+    cli_server "-w 2 test/rackup/hello.ru", config: <<RUBY
+worker_culling_strategy :oldest
+fork_worker
+RUBY
+
+    get_worker_pids # to consume server logs
+
+    Process.kill :TTIN, @pid
+
+    line = @server.gets
+    assert_match(/Worker 2 \(PID: \d+\) booted in/, line)
+
+    Process.kill :TTOU, @pid
+
+    line = @server.gets
+    assert_match(/Worker 1 \(PID: \d+\) terminating/, line)
+  end
+
   private
 
   def worker_timeout(timeout, iterations, details, config)

From 981658548cf5038730ff423d0c2cc13d532b2a2f Mon Sep 17 00:00:00 2001
From: shields <shields@tablecheck.com>
Date: Sun, 9 Jan 2022 20:13:29 +0900
Subject: [PATCH 2/4] Consider case where worker0 isn't oldest worker

---
 lib/puma/cluster.rb | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/puma/cluster.rb b/lib/puma/cluster.rb
index 749704aea0..c2afe20ba6 100644
--- a/lib/puma/cluster.rb
+++ b/lib/puma/cluster.rb
@@ -111,7 +111,9 @@ def cull_workers
 
       debug "Culling #{diff} workers"
 
-      workers_to_cull = @workers.sort_by(&:started_at)[cull_start_index(diff), diff]
+      workers_to_cull = @workers.sort_by(&:started_at)
+      workers_to_cull.reject! { |w| w.index == 0 } if @options[:fork_worker]
+      workers_to_cull = workers_to_cull[cull_start_index(diff), diff]
 
       debug "Workers to cull: #{workers_to_cull.inspect}"
 
@@ -124,7 +126,7 @@ def cull_workers
     def cull_start_index(diff)
       case @options[:worker_culling_strategy]
       when :oldest
-        @options[:fork_worker] ? 1 : 0
+        0
       else # :youngest
         -diff
       end

From 26330ce773a28e46cbe50b8451ce50c4b66082ac Mon Sep 17 00:00:00 2001
From: shields <shields@tablecheck.com>
Date: Sun, 9 Jan 2022 20:18:58 +0900
Subject: [PATCH 3/4] Reduce code complexity

---
 lib/puma/cluster.rb | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/lib/puma/cluster.rb b/lib/puma/cluster.rb
index c2afe20ba6..567398db11 100644
--- a/lib/puma/cluster.rb
+++ b/lib/puma/cluster.rb
@@ -108,21 +108,23 @@ def spawn_worker(idx, master)
     def cull_workers
       diff = @workers.size - @options[:workers]
       return if diff < 1
-
       debug "Culling #{diff} workers"
 
-      workers_to_cull = @workers.sort_by(&:started_at)
-      workers_to_cull.reject! { |w| w.index == 0 } if @options[:fork_worker]
-      workers_to_cull = workers_to_cull[cull_start_index(diff), diff]
-
-      debug "Workers to cull: #{workers_to_cull.inspect}"
+      workers = workers_to_cull(diff)
+      debug "Workers to cull: #{workers.inspect}"
 
-      workers_to_cull.each do |worker|
+      workers.each do |worker|
         log "- Worker #{worker.index} (PID: #{worker.pid}) terminating"
         worker.term
       end
     end
 
+    def workers_to_cull(diff)
+      workers = @workers.sort_by(&:started_at)
+      workers.reject! { |w| w.index == 0 } if @options[:fork_worker]
+      workers[cull_start_index(diff), diff]
+    end
+
     def cull_start_index(diff)
       case @options[:worker_culling_strategy]
       when :oldest

From e409a93324813b09cb4b8cfb913803266ee8877b Mon Sep 17 00:00:00 2001
From: Johnny Shields <johnny.shields@gmail.com>
Date: Mon, 10 Jan 2022 13:46:50 +0900
Subject: [PATCH 4/4] Add code comment

---
 lib/puma/cluster.rb | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/puma/cluster.rb b/lib/puma/cluster.rb
index 567398db11..5c3303a428 100644
--- a/lib/puma/cluster.rb
+++ b/lib/puma/cluster.rb
@@ -121,7 +121,11 @@ def cull_workers
 
     def workers_to_cull(diff)
       workers = @workers.sort_by(&:started_at)
+
+      # In fork_worker mode, worker 0 acts as our master process.
+      # We should avoid culling it to preserve copy-on-write memory gains.
       workers.reject! { |w| w.index == 0 } if @options[:fork_worker]
+
       workers[cull_start_index(diff), diff]
     end