diff --git a/crates/ruff_linter/src/registry/rule_set.rs b/crates/ruff_linter/src/registry/rule_set.rs
index a20f4ba0fd..7889ed81b5 100644
--- a/crates/ruff_linter/src/registry/rule_set.rs
+++ b/crates/ruff_linter/src/registry/rule_set.rs
@@ -207,6 +207,15 @@ impl RuleSet {
         *self = set.union(&RuleSet::from_rule(rule));
     }
 
+    #[inline]
+    pub fn set(&mut self, rule: Rule, enabled: bool) {
+        if enabled {
+            self.insert(rule);
+        } else {
+            self.remove(rule);
+        }
+    }
+
     /// Removes `rule` from the set.
     ///
     /// ## Examples
diff --git a/crates/ruff_workspace/src/configuration.rs b/crates/ruff_workspace/src/configuration.rs
index 7d175bf673..ec3bdbb228 100644
--- a/crates/ruff_workspace/src/configuration.rs
+++ b/crates/ruff_workspace/src/configuration.rs
@@ -867,11 +867,7 @@ impl LintConfiguration {
             } else {
                 // Otherwise we apply the updates on top of the existing select_set.
                 for (rule, enabled) in select_map_updates {
-                    if enabled {
-                        select_set.insert(rule);
-                    } else {
-                        select_set.remove(rule);
-                    }
+                    select_set.set(rule, enabled);
                 }
 
                 for rule in docstring_override_updates {
@@ -894,11 +890,7 @@ impl LintConfiguration {
                 }
             } else {
                 for (rule, enabled) in fixable_map_updates {
-                    if enabled {
-                        fixable_set.insert(rule);
-                    } else {
-                        fixable_set.remove(rule);
-                    }
+                    fixable_set.set(rule, enabled);
                 }
             }
 
@@ -1095,31 +1087,27 @@ impl LintConfiguration {
 
     #[must_use]
     pub fn combine(self, config: Self) -> Self {
+        let mut rule_selections = config.rule_selections;
+        rule_selections.extend(self.rule_selections);
+
+        let mut extend_safe_fixes = config.extend_safe_fixes;
+        extend_safe_fixes.extend(self.extend_safe_fixes);
+
+        let mut extend_unsafe_fixes = config.extend_unsafe_fixes;
+        extend_unsafe_fixes.extend(self.extend_unsafe_fixes);
+
+        let mut extend_per_file_ignores = config.extend_per_file_ignores;
+        extend_per_file_ignores.extend(self.extend_per_file_ignores);
+
         Self {
             exclude: self.exclude.or(config.exclude),
             preview: self.preview.or(config.preview),
-            rule_selections: config
-                .rule_selections
-                .into_iter()
-                .chain(self.rule_selections)
-                .collect(),
-            extend_safe_fixes: config
-                .extend_safe_fixes
-                .into_iter()
-                .chain(self.extend_safe_fixes)
-                .collect(),
-            extend_unsafe_fixes: config
-                .extend_unsafe_fixes
-                .into_iter()
-                .chain(self.extend_unsafe_fixes)
-                .collect(),
+            rule_selections,
+            extend_safe_fixes,
+            extend_unsafe_fixes,
             allowed_confusables: self.allowed_confusables.or(config.allowed_confusables),
             dummy_variable_rgx: self.dummy_variable_rgx.or(config.dummy_variable_rgx),
-            extend_per_file_ignores: config
-                .extend_per_file_ignores
-                .into_iter()
-                .chain(self.extend_per_file_ignores)
-                .collect(),
+            extend_per_file_ignores,
             external: self.external.or(config.external),
             ignore_init_module_imports: self
                 .ignore_init_module_imports
diff --git a/crates/ruff_workspace/src/resolver.rs b/crates/ruff_workspace/src/resolver.rs
index bc5ec2e715..26791117fe 100644
--- a/crates/ruff_workspace/src/resolver.rs
+++ b/crates/ruff_workspace/src/resolver.rs
@@ -335,6 +335,12 @@ pub fn python_files_in_path<'a>(
     // Search for `pyproject.toml` files in all parent directories.
     let mut resolver = Resolver::new(pyproject_config);
     let mut seen = FxHashSet::default();
+
+    // Insert the path to the root configuration to avoid parsing the configuration a second time.
+    if let Some(config_path) = &pyproject_config.path {
+        seen.insert(config_path.parent().unwrap());
+    }
+
     if resolver.is_hierarchical() {
         for path in &paths {
             for ancestor in path.ancestors() {
@@ -343,8 +349,12 @@ pub fn python_files_in_path<'a>(
                         let (root, settings) =
                             resolve_scoped_settings(&pyproject, Relativity::Parent, transformer)?;
                         resolver.add(root, settings);
+                        // We found the closest configuration.
                         break;
                     }
+                } else {
+                    // We already visited this ancestor, we can stop here.
+                    break;
                 }
             }
         }