diff --git a/plugin/vscode/quick-lint-js/vscode/qljs-workspace.cpp b/plugin/vscode/quick-lint-js/vscode/qljs-workspace.cpp
index f4b629cdd2..432045936c 100644
--- a/plugin/vscode/quick-lint-js/vscode/qljs-workspace.cpp
+++ b/plugin/vscode/quick-lint-js/vscode/qljs-workspace.cpp
@@ -372,7 +372,10 @@ void QLJS_Workspace::check_for_config_file_changes_from_thread(
 }
 
 void QLJS_Workspace::check_for_config_file_changes(::Napi::Env env) {
-  std::vector<Configuration_Change> changes = this->config_loader_.refresh();
+  Monotonic_Allocator temporary_allocator(
+      "QLJS_Workspace::check_for_config_file_changes");
+  Span<Configuration_Change> changes =
+      this->config_loader_.refresh(&temporary_allocator);
   for (const Configuration_Change& change : changes) {
     QLJS_DEBUG_LOG("Configuration changed for %s\n",
                    change.watched_path->c_str());
diff --git a/src/quick-lint-js/configuration/configuration-loader.cpp b/src/quick-lint-js/configuration/configuration-loader.cpp
index 58ea653658..658a902d1b 100644
--- a/src/quick-lint-js/configuration/configuration-loader.cpp
+++ b/src/quick-lint-js/configuration/configuration-loader.cpp
@@ -315,8 +315,10 @@ void Configuration_Loader::unwatch_all_files() {
   this->watched_input_paths_.clear();
 }
 
-std::vector<Configuration_Change> Configuration_Loader::refresh() {
-  std::vector<Configuration_Change> changes;
+Span<Configuration_Change> Configuration_Loader::refresh(
+    Monotonic_Allocator* allocator) {
+  Vector<Configuration_Change> changes("Configuration_Loader::refresh changes",
+                                       allocator);
 
   Hash_Map<Canonical_Path, Loaded_Config_File> loaded_config_files =
       std::move(this->loaded_config_files_);
@@ -515,7 +517,7 @@ std::vector<Configuration_Change> Configuration_Loader::refresh() {
     }
   }
 
-  return changes;
+  return changes.release_to_span();
 }
 
 bool Configuration_Loader::is_config_file_path(
diff --git a/src/quick-lint-js/configuration/configuration-loader.h b/src/quick-lint-js/configuration/configuration-loader.h
index f26c04107e..2492243869 100644
--- a/src/quick-lint-js/configuration/configuration-loader.h
+++ b/src/quick-lint-js/configuration/configuration-loader.h
@@ -10,12 +10,14 @@
 #include <optional>
 #include <quick-lint-js/configuration/configuration.h>
 #include <quick-lint-js/container/hash-map.h>
+#include <quick-lint-js/container/monotonic-allocator.h>
 #include <quick-lint-js/container/result.h>
 #include <quick-lint-js/container/vector.h>
 #include <quick-lint-js/diag/buffering-diag-reporter.h>
 #include <quick-lint-js/io/file-canonical.h>
 #include <quick-lint-js/io/file.h>
 #include <quick-lint-js/port/memory-resource.h>
+#include <quick-lint-js/port/span.h>
 #include <string>
 #include <string_view>
 #include <vector>
@@ -140,7 +142,7 @@ class Configuration_Loader {
   //   quick-lint-js.config's content changed.
   // * A quick-lint-js.config file didn't exist, and now one does.
   // * A quick-lint-js.config file was moved into an ancestor directory.
-  std::vector<Configuration_Change> refresh();
+  Span<Configuration_Change> refresh(Monotonic_Allocator*);
 
   // Returns true if the path might possibly be a configuration file detected by
   // load_for_file or watch_and_load_for_file.
diff --git a/src/quick-lint-js/lsp/lsp-server.cpp b/src/quick-lint-js/lsp/lsp-server.cpp
index d862ee4519..a3d2247ae4 100644
--- a/src/quick-lint-js/lsp/lsp-server.cpp
+++ b/src/quick-lint-js/lsp/lsp-server.cpp
@@ -219,12 +219,13 @@ void Linting_LSP_Server_Handler::handle_notification(
 }
 
 void Linting_LSP_Server_Handler::filesystem_changed() {
-  std::vector<Configuration_Change> config_changes =
-      this->config_loader_.refresh();
+  Monotonic_Allocator temporary_allocator(
+      "Linting_LSP_Server_Handler::filesystem_changed");
+  Span<Configuration_Change> config_changes =
+      this->config_loader_.refresh(&temporary_allocator);
   {
     Lock_Ptr<LSP_Documents> documents = this->documents_.lock();
-    this->handle_config_file_changes(
-        documents, Span<const Configuration_Change>(config_changes));
+    this->handle_config_file_changes(documents, config_changes);
   }
 }
 
@@ -366,10 +367,12 @@ void Linting_LSP_Server_Handler::handle_text_document_did_change_notification(
 
   switch (doc.type) {
   case LSP_Documents::Document_Type::config: {
-    std::vector<Configuration_Change> config_changes =
-        this->config_loader_.refresh();
-    this->handle_config_file_changes(
-        documents, Span<const Configuration_Change>(config_changes));
+    Monotonic_Allocator temporary_allocator(
+        "Linting_LSP_Server_Handler::handle_text_document_did_change_"
+        "notification");
+    Span<Configuration_Change> config_changes =
+        this->config_loader_.refresh(&temporary_allocator);
+    this->handle_config_file_changes(documents, config_changes);
     break;
   }
 
@@ -516,12 +519,14 @@ void Linting_LSP_Server_Handler::handle_text_document_did_open_notification(
         *config_file, notification.uri.json, doc->version_json,
         config_diagnostics_json);
 
-    std::vector<Configuration_Change> config_changes =
-        this->config_loader_.refresh();
+    Monotonic_Allocator temporary_allocator(
+        "Linting_LSP_Server_Handler::handle_text_document_did_open_"
+        "notification");
+    Span<Configuration_Change> config_changes =
+        this->config_loader_.refresh(&temporary_allocator);
     {
       Lock_Ptr<LSP_Documents> documents = this->documents_.lock();
-      this->handle_config_file_changes(
-          documents, Span<const Configuration_Change>(config_changes));
+      this->handle_config_file_changes(documents, config_changes);
     }
 
     doc_ptr = std::move(doc);
diff --git a/test/test-configuration-loader.cpp b/test/test-configuration-loader.cpp
index e20ffd4113..005dcbf26e 100644
--- a/test/test-configuration-loader.cpp
+++ b/test/test-configuration-loader.cpp
@@ -149,7 +149,7 @@ class Change_Detecting_Configuration_Loader {
     return this->fs_.take_watch_errors();
   }
 
-  std::vector<Configuration_Change> detect_changes_and_refresh();
+  Span<Configuration_Change> detect_changes_and_refresh();
 
  private:
   bool detect_changes();
@@ -187,6 +187,7 @@ class Change_Detecting_Configuration_Loader {
 
   // Protected by mutex_ if present:
   Configuration_Loader loader_;
+  Monotonic_Allocator allocator{"Change_Detecting_Configuration_Loader"};
 };
 
 class Test_Configuration_Loader : public ::testing::Test,
@@ -643,8 +644,7 @@ TEST_F(Test_Configuration_Loader,
   EXPECT_EQ(::rmdir(parent_dir.c_str()), 0)
       << "failed to delete " << parent_dir << ": " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -659,8 +659,7 @@ TEST_F(Test_Configuration_Loader, config_found_initially_is_unchanged) {
     Change_Detecting_Configuration_Loader loader;
     loader.watch_and_load_for_file(js_file, /*token=*/nullptr);
 
-    std::vector<Configuration_Change> changes =
-        loader.detect_changes_and_refresh();
+    Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
     EXPECT_THAT(changes, IsEmpty());
   }
 }
@@ -678,8 +677,7 @@ TEST_F(Test_Configuration_Loader,
 
   write_file_or_exit(config_file, u8R"({"globals": {"after": true}})"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, config_file);
@@ -708,8 +706,7 @@ TEST_F(Test_Configuration_Loader,
     ASSERT_EQ(std::fclose(file), 0) << std::strerror(errno);
   }
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, config_file);
@@ -729,8 +726,7 @@ TEST_F(Test_Configuration_Loader,
   write_file_or_exit(config_file, u8R"({"globals": {"b": true}})"_sv);
   write_file_or_exit(config_file, u8R"({"globals": {"a": true}})"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -751,8 +747,7 @@ TEST_F(Test_Configuration_Loader,
 
   move_file(new_config_file, config_file);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, config_file);
@@ -775,8 +770,7 @@ TEST_F(Test_Configuration_Loader,
 
   move_file(new_config_file, config_file);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -795,8 +789,7 @@ TEST_F(Test_Configuration_Loader,
   move_file(config_file, temp_config_file);
   move_file(temp_config_file, config_file);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -811,8 +804,7 @@ TEST_F(Test_Configuration_Loader, creating_config_in_same_dir_is_detected) {
   std::string config_file = project_dir + "/quick-lint-js.config";
   write_file_or_exit(config_file, u8"{}"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, config_file);
@@ -829,8 +821,7 @@ TEST_F(Test_Configuration_Loader,
   std::string config_file = project_dir + "/quick-lint-js.config";
   write_file_or_exit(config_file, u8"{}"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_THAT(*changes[0].watched_path, ::testing::HasSubstr("hello.js"));
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, config_file);
@@ -848,8 +839,7 @@ TEST_F(Test_Configuration_Loader, creating_config_in_parent_dir_is_detected) {
   std::string config_file = project_dir + "/quick-lint-js.config";
   write_file_or_exit(config_file, u8"{}"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, config_file);
@@ -870,8 +860,7 @@ TEST_F(Test_Configuration_Loader,
   std::string inner_config_file = project_dir + "/dir/quick-lint-js.config";
   write_file_or_exit(inner_config_file, u8"{}"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, inner_config_file);
@@ -890,8 +879,7 @@ TEST_F(Test_Configuration_Loader, deleting_config_in_same_dir_is_detected) {
   EXPECT_EQ(std::remove(config_file.c_str()), 0)
       << "failed to delete " << config_file << ": " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_EQ(changes[0].config_file, nullptr);
@@ -915,8 +903,7 @@ TEST_F(Test_Configuration_Loader,
       << "failed to delete " << inner_config_file << ": "
       << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, outer_config_file);
@@ -934,8 +921,7 @@ TEST_F(Test_Configuration_Loader, moving_config_away_in_same_dir_is_detected) {
 
   move_file(config_file, (project_dir + "/moved.config"));
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_EQ(changes[0].config_file, nullptr);
@@ -957,8 +943,7 @@ TEST_F(Test_Configuration_Loader,
 
   move_file(inner_config_file, (project_dir + "/dir/moved.config"));
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, outer_config_file);
@@ -977,8 +962,7 @@ TEST_F(Test_Configuration_Loader, moving_config_into_same_dir_is_detected) {
 
   move_file(temp_config_file, renamed_config_file);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, renamed_config_file);
@@ -998,8 +982,7 @@ TEST_F(Test_Configuration_Loader, moving_config_into_parent_dir_is_detected) {
 
   move_file(temp_config_file, renamed_config_file);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, renamed_config_file);
@@ -1022,8 +1005,7 @@ TEST_F(Test_Configuration_Loader,
 
   move_file(temp_config_file, inner_config_file);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_SAME_FILE(*changes[0].watched_path, js_file);
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, inner_config_file);
@@ -1043,8 +1025,7 @@ TEST_F(Test_Configuration_Loader,
 
   move_file((project_dir + "/olddir"), (project_dir + "/newdir"));
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_THAT(*changes[0].watched_path, ::testing::HasSubstr("hello.js"));
   EXPECT_THAT(*changes[0].watched_path, ::testing::HasSubstr("olddir"));
@@ -1066,8 +1047,7 @@ TEST_F(Test_Configuration_Loader,
 
   move_file((project_dir + "/olddir"), (project_dir + "/newdir"));
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_THAT(*changes[0].watched_path, ::testing::HasSubstr("hello.js"));
   EXPECT_THAT(*changes[0].watched_path, ::testing::HasSubstr("olddir"));
@@ -1088,8 +1068,7 @@ TEST_F(Test_Configuration_Loader,
 
   move_file((project_dir + "/olddir"), (project_dir + "/newdir"));
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -1105,8 +1084,7 @@ TEST_F(Test_Configuration_Loader, moving_file_keeps_config) {
 
   move_file((project_dir + "/oldfile.js"), (project_dir + "/newfile.js"));
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -1119,8 +1097,7 @@ TEST_F(Test_Configuration_Loader,
   loader.watch_and_load_for_file(js_file, /*token=*/nullptr);
 
   create_directory_or_exit(project_dir + "/dir");
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty())
       << "creating dir should not change associated config file";
 
@@ -1147,8 +1124,7 @@ TEST_F(
   std::string config_file = project_dir + "/dir/quick-lint-js.config";
   write_file_or_exit(config_file, u8"{}"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_THAT(*changes[0].watched_path, ::testing::HasSubstr("test.js"));
   EXPECT_SAME_FILE(*changes[0].config_file->config_path, config_file);
@@ -1174,8 +1150,7 @@ TEST_F(Test_Configuration_Loader,
   std::string config_file = project_dir + "/quick-lint-js.config";
   write_file_or_exit(config_file, u8"{}"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   Hash_Set<std::string> unconfigured_js_files = js_files;
   for (const Configuration_Change& change : changes) {
     SCOPED_TRACE(*change.watched_path);
@@ -1218,8 +1193,7 @@ TEST_F(Test_Configuration_Loader,
       << std::strerror(errno);
   write_file_or_exit(outer_config_file, u8R"({"globals": {"after": true}})"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
 
   std::vector<std::string> watched_paths;
   std::vector<void*> watched_tokens;
@@ -1266,8 +1240,7 @@ TEST_F(Test_Configuration_Loader,
 
   write_file_or_exit(config_file, u8R"({"globals": {"after": true}})"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(*changes[0].watched_path, config_file);
   EXPECT_EQ(changes[0].token, &config_file);
@@ -1289,8 +1262,7 @@ TEST_F(Test_Configuration_Loader,
   write_file_or_exit(config_file,
                      u8R"({"globals": {"testGlobalVariable": true}})"_sv);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(*changes[0].watched_path, config_file);
   EXPECT_EQ(changes[0].token, &config_file);
@@ -1312,8 +1284,7 @@ TEST_F(Test_Configuration_Loader,
   EXPECT_EQ(std::remove(config_file.c_str()), 0)
       << "failed to delete " << config_file << ": " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(*changes[0].watched_path, config_file);
   EXPECT_EQ(changes[0].token, &config_file);
@@ -1407,8 +1378,7 @@ TEST_F(Test_Configuration_Loader,
       << "failed to make " << config_file
       << " unreadable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &js_file);
   EXPECT_EQ(changes[0].config_file, nullptr);
@@ -1439,8 +1409,7 @@ TEST_F(Test_Configuration_Loader,
       << "failed to make " << config_file
       << " unreadable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &config_file);
   EXPECT_EQ(changes[0].config_file, nullptr);
@@ -1485,8 +1454,7 @@ TEST_F(Test_Configuration_Loader,
       << "failed to make " << config_file
       << " readable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &js_file);
   EXPECT_TRUE(
@@ -1528,8 +1496,7 @@ TEST_F(Test_Configuration_Loader,
       << "failed to make " << config_file
       << " readable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &config_file);
   EXPECT_TRUE(
@@ -1562,8 +1529,7 @@ TEST_F(Test_Configuration_Loader,
             canonicalize_path(config_file)->c_str());
   EXPECT_EQ(loaded_config.error().io_error.error, EACCES);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -1589,8 +1555,7 @@ TEST_F(Test_Configuration_Loader,
               canonicalize_path(config_file)->c_str());
   EXPECT_THAT(loaded_config.error().io_error.error, EACCES);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -1615,15 +1580,14 @@ TEST_F(Test_Configuration_Loader,
       << "failed to make " << config_file
       << " unreadable: " << std::strerror(errno);
 
-  [[maybe_unused]] std::vector<Configuration_Change> changes_1 =
+  [[maybe_unused]] Span<Configuration_Change> changes_1 =
       loader.detect_changes_and_refresh();
 
   EXPECT_EQ(::chmod(config_file.c_str(), 0644), 0)
       << "failed to make " << config_file
       << " readable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes_2 =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes_2 = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes_2, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes_2[0].token, &js_file);
   EXPECT_TRUE(changes_2[0].config_file->config.globals().find(
@@ -1650,15 +1614,14 @@ TEST_F(
       << "failed to make " << config_file
       << " unreadable: " << std::strerror(errno);
 
-  [[maybe_unused]] std::vector<Configuration_Change> changes_1 =
+  [[maybe_unused]] Span<Configuration_Change> changes_1 =
       loader.detect_changes_and_refresh();
 
   EXPECT_EQ(::chmod(config_file.c_str(), 0644), 0)
       << "failed to make " << config_file
       << " readable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes_2 =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes_2 = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes_2, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes_2[0].token, &config_file);
   EXPECT_TRUE(changes_2[0].config_file->config.globals().find(
@@ -1702,15 +1665,14 @@ TEST_F(
       << "failed to make " << config_file
       << " readable: " << std::strerror(errno);
 
-  [[maybe_unused]] std::vector<Configuration_Change> changes_1 =
+  [[maybe_unused]] Span<Configuration_Change> changes_1 =
       loader.detect_changes_and_refresh();
 
   EXPECT_EQ(::chmod(config_file.c_str(), 0000), 0)
       << "failed to make " << config_file
       << " unreadable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes_2 =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes_2 = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes_2, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes_2[0].token, &js_file);
   EXPECT_EQ(changes_2[0].config_file, nullptr);
@@ -1752,15 +1714,14 @@ TEST_F(
       << "failed to make " << config_file
       << " readable: " << std::strerror(errno);
 
-  [[maybe_unused]] std::vector<Configuration_Change> changes_1 =
+  [[maybe_unused]] Span<Configuration_Change> changes_1 =
       loader.detect_changes_and_refresh();
 
   EXPECT_EQ(::chmod(config_file.c_str(), 0000), 0)
       << "failed to make " << config_file
       << " unreadable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes_2 =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes_2 = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes_2, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes_2[0].token, &config_file);
   EXPECT_EQ(changes_2[0].config_file, nullptr);
@@ -1799,8 +1760,7 @@ TEST_F(Test_Configuration_Loader,
   EXPECT_EQ(::chmod(dir.c_str(), 0700), 0)
       << "failed to make " << dir << " readable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &js_file);
   EXPECT_TRUE(
@@ -1838,8 +1798,7 @@ TEST_F(
   EXPECT_EQ(::chmod(dir.c_str(), 0700), 0)
       << "failed to make " << dir << " readable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &config_file);
   EXPECT_TRUE(
@@ -1874,8 +1833,7 @@ TEST_F(Test_Configuration_Loader,
   EXPECT_EQ(::chmod(dir.c_str(), 0600), 0)
       << "failed to make " << dir << " unreadable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &js_file);
   EXPECT_EQ(changes[0].config_file, nullptr);
@@ -1912,8 +1870,7 @@ TEST_F(
   EXPECT_EQ(::chmod(dir.c_str(), 0600), 0)
       << "failed to make " << dir << " unreadable: " << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &config_file);
   EXPECT_EQ(changes[0].config_file, nullptr);
@@ -1950,8 +1907,7 @@ TEST_F(Test_Configuration_Loader,
   EXPECT_EQ(loaded_config.error().canonicalizing_path, js_file_canonical_path);
   EXPECT_EQ(loaded_config.error().io_error.error, EACCES);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 
@@ -1981,8 +1937,7 @@ TEST_F(Test_Configuration_Loader,
             config_file_canonical_path);
   EXPECT_EQ(loaded_config.error().io_error.error, EACCES);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   EXPECT_THAT(changes, IsEmpty());
 }
 #endif
@@ -2008,8 +1963,7 @@ TEST_F(Test_Configuration_Loader,
   ASSERT_EQ(::symlink("after.config", config_symlink.c_str()), 0)
       << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(changes[0].token, &config_symlink);
   EXPECT_EQ(*changes[0].config_file->config_path,
@@ -2043,8 +1997,7 @@ TEST_F(Test_Configuration_Loader,
   ASSERT_EQ(::symlink("after", subdir_symlink.c_str()), 0)
       << std::strerror(errno);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(*changes[0].config_file->config_path,
             canonicalize_path(after_config_file)->canonical());
@@ -2075,8 +2028,7 @@ TEST_F(Test_Configuration_Loader,
   move_file(subdir, project_dir + "/before");
   move_file(project_dir + "/after", subdir);
 
-  std::vector<Configuration_Change> changes =
-      loader.detect_changes_and_refresh();
+  Span<Configuration_Change> changes = loader.detect_changes_and_refresh();
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_EQ(*changes[0].config_file->config_path,
             canonicalize_path(subdir + "/quick-lint-js.config")->canonical());
@@ -2205,8 +2157,13 @@ TEST_F(Test_Configuration_Loader,
 }
 #endif
 
-TEST(Test_Configuration_Loader_Fake,
-     file_with_no_config_file_gets_default_config) {
+class Test_Configuration_Loader_Fake : public ::testing::Test {
+ public:
+  Monotonic_Allocator allocator{"Test_Configuration_Loader_Fake"};
+};
+
+TEST_F(Test_Configuration_Loader_Fake,
+       file_with_no_config_file_gets_default_config) {
   Fake_Configuration_Filesystem fs;
   fs.create_file(fs.rooted("hello.js"), u8""_sv);
 
@@ -2219,8 +2176,8 @@ TEST(Test_Configuration_Loader_Fake,
   EXPECT_EQ(*loaded_config, nullptr);
 }
 
-TEST(Test_Configuration_Loader_Fake,
-     find_quick_lint_js_config_in_same_directory) {
+TEST_F(Test_Configuration_Loader_Fake,
+       find_quick_lint_js_config_in_same_directory) {
   Fake_Configuration_Filesystem fs;
   fs.create_file(fs.rooted("hello.js"), u8""_sv);
   fs.create_file(fs.rooted("quick-lint-js.config"), u8"{}"_sv);
@@ -2235,7 +2192,7 @@ TEST(Test_Configuration_Loader_Fake,
   EXPECT_EQ(*(*loaded_config)->config_path, fs.rooted("quick-lint-js.config"));
 }
 
-TEST(Test_Configuration_Loader_Fake, find_config_in_parent_directory) {
+TEST_F(Test_Configuration_Loader_Fake, find_config_in_parent_directory) {
   Fake_Configuration_Filesystem fs;
   fs.create_file(fs.rooted("dir/hello.js"), u8""_sv);
   fs.create_file(fs.rooted("quick-lint-js.config"), u8"{}"_sv);
@@ -2250,8 +2207,8 @@ TEST(Test_Configuration_Loader_Fake, find_config_in_parent_directory) {
   EXPECT_EQ(*(*loaded_config)->config_path, fs.rooted("quick-lint-js.config"));
 }
 
-TEST(Test_Configuration_Loader_Fake,
-     adding_json_syntax_error_makes_config_default) {
+TEST_F(Test_Configuration_Loader_Fake,
+       adding_json_syntax_error_makes_config_default) {
   Fake_Configuration_Filesystem fs;
   fs.create_file(fs.rooted("hello.js"), u8""_sv);
   fs.create_file(fs.rooted("quick-lint-js.config"), u8"{}"_sv);
@@ -2264,13 +2221,13 @@ TEST(Test_Configuration_Loader_Fake,
   ASSERT_TRUE((*loaded_config)->config.globals().find(u8"console"_sv));
 
   fs.create_file(fs.rooted("quick-lint-js.config"), u8"{\\}"_sv);
-  std::vector<Configuration_Change> changes = loader.refresh();
+  Span<Configuration_Change> changes = loader.refresh(&this->allocator);
   ASSERT_THAT(changes, ElementsAreArray({::testing::_}));
   EXPECT_TRUE(changes[0].config_file->config.globals().find(u8"console"_sv));
 }
 
-TEST(Test_Configuration_Loader_Fake,
-     multiple_watches_for_same_token_are_notified_together) {
+TEST_F(Test_Configuration_Loader_Fake,
+       multiple_watches_for_same_token_are_notified_together) {
   Fake_Configuration_Filesystem fs;
   fs.create_file(fs.rooted("quick-lint-js.config"), u8"{}"_sv);
   char token_1;
@@ -2284,7 +2241,7 @@ TEST(Test_Configuration_Loader_Fake,
 
   fs.create_file(fs.rooted("quick-lint-js.config"),
                  u8"{\"_svglobal-groups\": false}"_sv);
-  std::vector<Configuration_Change> changes = loader.refresh();
+  Span<Configuration_Change> changes = loader.refresh(&this->allocator);
   std::vector<void*> tokens;
   for (Configuration_Change& change : changes) {
     tokens.push_back(change.token);
@@ -2293,10 +2250,14 @@ TEST(Test_Configuration_Loader_Fake,
               ::testing::UnorderedElementsAreArray({&token_1, &token_2}));
 }
 
-std::vector<Configuration_Change>
+Span<Configuration_Change>
 Change_Detecting_Configuration_Loader::detect_changes_and_refresh() {
+#if defined(_WIN32)
+  std::lock_guard<Mutex> lock(this->mutex_);
+#endif
   bool fs_changed = this->detect_changes();
-  std::vector<Configuration_Change> config_changes = this->loader_.refresh();
+  Span<Configuration_Change> config_changes =
+      this->loader_.refresh(&this->allocator);
   if (fs_changed) {
     // NOTE(strager): We cannot assert that at least one change happened,
     // because filesystem notifications might be spurious.