diff --git a/app/controllers/uploads_controller.rb b/app/controllers/uploads_controller.rb
index 060b09f015c..5d28635232b 100644
--- a/app/controllers/uploads_controller.rb
+++ b/app/controllers/uploads_controller.rb
@@ -45,7 +45,7 @@ class UploadsController < ApplicationController
       when Appearance
         true
       else
-        permission = "read_#{model.class.to_s.underscore}".to_sym
+        permission = "read_#{model.class.underscore}".to_sym
 
         can?(current_user, permission, model)
       end
diff --git a/app/models/application_record.rb b/app/models/application_record.rb
index d1d01368972..0979d03f6e6 100644
--- a/app/models/application_record.rb
+++ b/app/models/application_record.rb
@@ -41,4 +41,8 @@ class ApplicationRecord < ActiveRecord::Base
       find_or_create_by(*args)
     end
   end
+
+  def self.underscore
+    Gitlab::SafeRequestStore.fetch("model:#{self}:underscore") { self.to_s.underscore }
+  end
 end
diff --git a/app/uploaders/attachment_uploader.rb b/app/uploaders/attachment_uploader.rb
index 0a166335b4e..b488bba00e9 100644
--- a/app/uploaders/attachment_uploader.rb
+++ b/app/uploaders/attachment_uploader.rb
@@ -9,6 +9,6 @@ class AttachmentUploader < GitlabUploader
   private
 
   def dynamic_segment
-    File.join(model.class.to_s.underscore, mounted_as.to_s, model.id.to_s)
+    File.join(model.class.underscore, mounted_as.to_s, model.id.to_s)
   end
 end
diff --git a/app/uploaders/avatar_uploader.rb b/app/uploaders/avatar_uploader.rb
index c0165759203..9af59b0aceb 100644
--- a/app/uploaders/avatar_uploader.rb
+++ b/app/uploaders/avatar_uploader.rb
@@ -25,6 +25,6 @@ class AvatarUploader < GitlabUploader
   private
 
   def dynamic_segment
-    File.join(model.class.to_s.underscore, mounted_as.to_s, model.id.to_s)
+    File.join(model.class.underscore, mounted_as.to_s, model.id.to_s)
   end
 end
diff --git a/app/uploaders/personal_file_uploader.rb b/app/uploaders/personal_file_uploader.rb
index 272837aa6ce..f4697d898af 100644
--- a/app/uploaders/personal_file_uploader.rb
+++ b/app/uploaders/personal_file_uploader.rb
@@ -20,7 +20,7 @@ class PersonalFileUploader < FileUploader
   def self.model_path_segment(model)
     return 'temp/' unless model
 
-    File.join(model.class.to_s.underscore, model.id.to_s)
+    File.join(model.class.underscore, model.id.to_s)
   end
 
   def object_store
diff --git a/changelogs/unreleased/make-autocomplete-faster-with-lots-of-results.yml b/changelogs/unreleased/make-autocomplete-faster-with-lots-of-results.yml
new file mode 100644
index 00000000000..daeefd3ffd7
--- /dev/null
+++ b/changelogs/unreleased/make-autocomplete-faster-with-lots-of-results.yml
@@ -0,0 +1,5 @@
+---
+title: Improve performance of users autocomplete when there are lots of results
+merge_request:
+author:
+type: performance
diff --git a/spec/controllers/concerns/send_file_upload_spec.rb b/spec/controllers/concerns/send_file_upload_spec.rb
index 8408578a7db..a3ce08f736c 100644
--- a/spec/controllers/concerns/send_file_upload_spec.rb
+++ b/spec/controllers/concerns/send_file_upload_spec.rb
@@ -1,3 +1,4 @@
+# coding: utf-8
 # frozen_string_literal: true
 
 require 'spec_helper'
@@ -13,7 +14,7 @@ describe SendFileUpload do
 
       # user/:id
       def dynamic_segment
-        File.join(model.class.to_s.underscore, model.id.to_s)
+        File.join(model.class.underscore, model.id.to_s)
       end
     end
   end
diff --git a/spec/factories/uploads.rb b/spec/factories/uploads.rb
index 7256f785e1f..426abdc2a6c 100644
--- a/spec/factories/uploads.rb
+++ b/spec/factories/uploads.rb
@@ -13,7 +13,7 @@ FactoryBot.define do
     end
 
     # this needs to comply with RecordsUpload::Concern#upload_path
-    path { File.join("uploads/-/system", model.class.to_s.underscore, mount_point.to_s, 'avatar.jpg') }
+    path { File.join("uploads/-/system", model.class.underscore, mount_point.to_s, 'avatar.jpg') }
 
     trait :personal_snippet_upload do
       uploader "PersonalFileUploader"
diff --git a/spec/models/application_record_spec.rb b/spec/models/application_record_spec.rb
index cc90a998d3f..74573d0941c 100644
--- a/spec/models/application_record_spec.rb
+++ b/spec/models/application_record_spec.rb
@@ -52,4 +52,10 @@ describe ApplicationRecord do
       expect { Suggestion.find_or_create_by!(note: nil) }.to raise_error(ActiveRecord::RecordInvalid)
     end
   end
+
+  describe '.underscore' do
+    it 'returns the underscored value of the class as a string' do
+      expect(MergeRequest.underscore).to eq('merge_request')
+    end
+  end
 end
diff --git a/spec/uploaders/object_storage_spec.rb b/spec/uploaders/object_storage_spec.rb
index a62830c35f1..6bad5d49b1c 100644
--- a/spec/uploaders/object_storage_spec.rb
+++ b/spec/uploaders/object_storage_spec.rb
@@ -12,7 +12,7 @@ class Implementation < GitlabUploader
 
   # user/:id
   def dynamic_segment
-    File.join(model.class.to_s.underscore, model.id.to_s)
+    File.join(model.class.underscore, model.id.to_s)
   end
 end