From 36343b5400647893ffb8d5db0a0245ff8b3f6871 Mon Sep 17 00:00:00 2001
From: Ikraam Ghoor <ikraamghoor@gmail.com>
Date: Mon, 21 Sep 2026 09:26:44 +0200
Subject: [PATCH] Mix PageableResponse into Seahorse::Client::Response instead
 of extending each response

Kernel#extend gives the response a singleton class and clears the method
cache for every method the extension defines (each, count, to_h,
respond_to?, and all of Enumerable), process-wide, on every request.
Under YJIT that discards every compiled block that relied on one of
those names being absent; a Rails app signing one S3 URL per request
measured ~4 invalidations and 2.3 KB of regenerated code per URL, and
its workers reached --yjit-mem-size within hours and stopped compiling.

Including the extension in the response class once keeps the same
interface on every response with no per-response work. apply still
extends other objects, so its constant cache guarantee is unchanged.
---
 gems/aws-sdk-core/CHANGELOG.md                |  2 ++
 .../lib/aws-sdk-core/pageable_response.rb     |  7 ++++++-
 .../spec/aws/pageable_response_spec.rb        | 21 +++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/gems/aws-sdk-core/CHANGELOG.md b/gems/aws-sdk-core/CHANGELOG.md
index e9eac7fa8e4..c7f09a60473 100644
--- a/gems/aws-sdk-core/CHANGELOG.md
+++ b/gems/aws-sdk-core/CHANGELOG.md
@@ -1,6 +1,8 @@
 Unreleased Changes
 ------------------
 
+* Issue - Mix `PageableResponse` into `Seahorse::Client::Response` once instead of extending every response object, which cleared Ruby's method cache for each of the extension's methods on every request and made YJIT discard compiled code.
+
 3.257.0 (2026-09-14)
 ------------------
 
diff --git a/gems/aws-sdk-core/lib/aws-sdk-core/pageable_response.rb b/gems/aws-sdk-core/lib/aws-sdk-core/pageable_response.rb
index 564054495c0..f2ca7f527ce 100644
--- a/gems/aws-sdk-core/lib/aws-sdk-core/pageable_response.rb
+++ b/gems/aws-sdk-core/lib/aws-sdk-core/pageable_response.rb
@@ -49,7 +49,7 @@ module Aws
   module PageableResponse
 
     def self.apply(base)
-      base.extend Extension
+      base.extend Extension unless Extension === base
       base.instance_variable_set(:@last_page, nil)
       base.instance_variable_set(:@more_results, nil)
       base
@@ -217,5 +217,10 @@ def next_page_params(params)
       end
 
     end
+
+    # Mixed into the response class once rather than extended onto each
+    # response: Kernel#extend clears the method cache for every method the
+    # extension defines, process-wide, on every request.
+    Seahorse::Client::Response.include(Extension)
   end
 end
diff --git a/gems/aws-sdk-core/spec/aws/pageable_response_spec.rb b/gems/aws-sdk-core/spec/aws/pageable_response_spec.rb
index 34fa1a77885..a8a082e2852 100644
--- a/gems/aws-sdk-core/spec/aws/pageable_response_spec.rb
+++ b/gems/aws-sdk-core/spec/aws/pageable_response_spec.rb
@@ -274,6 +274,27 @@ def pageable(resp, pager)
           PageableResponse.apply(object)
         }.to_not change { RubyVM.stat(key) }
       end
+
+      # Kernel#extend creates a singleton class and clears the method cache for every
+      # method the module defines (each, count, to_h, respond_to?, all of Enumerable...),
+      # process-wide, so it must not happen once per response.
+      it 'does not give a Seahorse::Client::Response a singleton class' do
+        skip 'Only applies to MRI' unless defined? RubyVM.stat
+
+        resp = Seahorse::Client::Response.new
+        GC.disable
+        classes_before = ObjectSpace.count_objects.values_at(:T_CLASS, :T_ICLASS)
+        PageableResponse.apply(resp)
+        expect(ObjectSpace.count_objects.values_at(:T_CLASS, :T_ICLASS)).to eq(classes_before)
+      ensure
+        GC.enable
+      end
+
+      it 'leaves every Seahorse::Client::Response pageable' do
+        resp = Seahorse::Client::Response.new
+        expect(resp).to be_kind_of(PageableResponse::Extension)
+        expect(resp).to be_kind_of(Enumerable)
+      end
     end
 
   end