reduce number of allocations (#2833)

VecDeque::new always allocates 7 elements

clippy.toml

@@ -8,4 +8,7 @@ disallowed-methods = [
   # sets), but the hash **is not stable** and must not be observed.
   # Use Xxh3Hash64Hasher::write with value's bytes directly.
   "std::hash::Hasher::hash",
+  # We forbid the use of VecDeque::new as it allocates, which is kind of unexpected
+  # Instead use VecDeque::with_capacity to make it explicit or opt-out of that.
+  "std::collections::VecDeque::new",
 ]

crates/turbo-tasks-memory/src/task.rs

@@ -1,7 +1,7 @@
 use std::{
     borrow::Cow,
     cell::RefCell,
-    cmp::Ordering,
+    cmp::{max, Ordering},
     collections::VecDeque,
     fmt::{self, Debug, Display, Formatter, Write},
     future::Future,
@@ -743,6 +743,9 @@ impl Task {
                     }
                 }
 
+                if queue.capacity() == 0 {
+                    queue.reserve(max(children.len(), SPLIT_OFF_QUEUE_AT * 2));
+                }
                 queue.extend(children.iter().copied().map(|child| (child, depth + 1)));
 
                 // add to dirty list of the scope (potentially schedule)
@@ -764,7 +767,8 @@ impl Task {
         backend: &MemoryBackend,
         turbo_tasks: &dyn TurboTasksBackendApi,
     ) {
-        let mut queue = VecDeque::new();
+        // VecDeque::new() would allocate with 7 items capacity. We don't want that.
+        let mut queue = VecDeque::with_capacity(0);
         self.add_to_scope_internal_shallow(
             id,
             is_optimization_scope,
@@ -908,6 +912,9 @@ impl Task {
             TaskScopes::Inner(ref mut set, _) => {
                 if set.remove(id) {
                     self.remove_self_from_scope(&mut state, id, backend, turbo_tasks);
+                    if queue.capacity() == 0 {
+                        queue.reserve(max(state.children.len(), SPLIT_OFF_QUEUE_AT * 2));
+                    }
                     queue.extend(state.children.iter().copied());
                     drop(state);
                 }
@@ -921,7 +928,8 @@ impl Task {
         backend: &MemoryBackend,
         turbo_tasks: &dyn TurboTasksBackendApi,
     ) {
-        let mut queue = VecDeque::new();
+        // VecDeque::new() would allocate with 7 items capacity. We don't want that.
+        let mut queue = VecDeque::with_capacity(0);
         self.remove_from_scope_internal_shallow(id, backend, turbo_tasks, &mut queue);
         run_remove_from_scope_queue(queue, id, backend, turbo_tasks);
     }
@@ -1540,8 +1548,8 @@ pub fn run_add_to_scope_queue(
                 &mut queue,
             );
         });
-        if queue.len() > SPLIT_OFF_QUEUE_AT {
-            let split_off_queue = queue.split_off(SPLIT_OFF_QUEUE_AT);
+        while queue.len() > SPLIT_OFF_QUEUE_AT {
+            let split_off_queue = queue.split_off(queue.len() - SPLIT_OFF_QUEUE_AT);
             turbo_tasks.schedule_backend_foreground_job(backend.create_backend_job(
                 Job::AddToScopeQueue(split_off_queue, id, is_optimization_scope),
             ));
@@ -1560,8 +1568,8 @@ pub fn run_remove_from_scope_queue(
         backend.with_task(child, |child| {
             child.remove_from_scope_internal_shallow(id, backend, turbo_tasks, &mut queue);
         });
-        if queue.len() > SPLIT_OFF_QUEUE_AT {
-            let split_off_queue = queue.split_off(SPLIT_OFF_QUEUE_AT);
+        while queue.len() > SPLIT_OFF_QUEUE_AT {
+            let split_off_queue = queue.split_off(queue.len() - SPLIT_OFF_QUEUE_AT);
 
             turbo_tasks.schedule_backend_foreground_job(
                 backend.create_backend_job(Job::RemoveFromScopeQueue(split_off_queue, id)),

crates/turbopack-core/src/chunk/mod.rs

@@ -346,7 +346,7 @@ async fn chunk_content_internal<I: FromChunkableAsset>(
     let mut chunks = Vec::new();
     let mut async_chunk_groups = Vec::new();
     let mut external_asset_references = Vec::new();
-    let mut queue = VecDeque::new();
+    let mut queue = VecDeque::with_capacity(32);
 
     let chunk_item = I::from_asset(context, entry).await?.unwrap();
     queue.push_back(ChunkContentWorkItem::AssetReferences(

crates/turbopack-core/src/reference/mod.rs

@@ -94,7 +94,7 @@ impl SingleAssetReferenceVc {
 pub async fn all_referenced_assets(asset: AssetVc) -> Result<AssetsVc> {
     let references_set = asset.references().await?;
     let mut assets = Vec::new();
-    let mut queue = VecDeque::new();
+    let mut queue = VecDeque::with_capacity(32);
     for reference in references_set.iter() {
         queue.push_back(reference.resolve_reference());
     }
@@ -137,7 +137,7 @@ pub async fn all_referenced_assets(asset: AssetVc) -> Result<AssetsVc> {
 #[turbo_tasks::function]
 pub async fn all_assets(asset: AssetVc) -> Result<AssetsVc> {
     // TODO need to track import path here
-    let mut queue = VecDeque::new();
+    let mut queue = VecDeque::with_capacity(32);
     queue.push_back((asset, all_referenced_assets(asset)));
     let mut assets = HashSet::new();
     assets.insert(asset);

crates/turbopack-create-test-app/src/test_app_builder.rs

@@ -82,7 +82,7 @@ const SETUP_EFFECT_PROPS: &str = indoc! {r#"
 let EFFECT_PROPS = {};
 "#};
 const SETUP_EVAL: &str = indoc! {r#"
-/* @turbopack-bench:eval-start */ 
+/* @turbopack-bench:eval-start */
 /* @turbopack-bench:eval-end */
 "#};
 const USE_EFFECT: &str = indoc! {r#"
@@ -115,7 +115,7 @@ impl TestAppBuilder {
         let mut remaining_directories = self.directories_count;
         let mut remaining_dynamic_imports = self.dynamic_import_count;
 
-        let mut queue = VecDeque::new();
+        let mut queue = VecDeque::with_capacity(32);
         queue.push_back((src.join("triangle.jsx"), 0));
         remaining_modules -= 1;
         let mut is_root = true;

crates/turbopack-dev-server/src/source/asset_graph.rs

@@ -91,7 +91,7 @@ impl AssetGraphContentSourceVc {
         let mut map = HashMap::new();
         let root_path = this.root_path.await?;
         let mut assets = Vec::new();
-        let mut queue = VecDeque::new();
+        let mut queue = VecDeque::with_capacity(32);
         let mut assets_set = HashSet::new();
         let root_assets = this.root_assets.await?;
         if let Some(state) = &this.state {

crates/turbopack-tests/tests/snapshot.rs

@@ -211,7 +211,7 @@ async fn run_test(resource: String) -> Result<FileSystemPathVc> {
         .await?;
 
     let mut seen = HashSet::new();
-    let mut queue = VecDeque::new();
+    let mut queue = VecDeque::with_capacity(32);
     for chunk in chunks {
         queue.push_back(chunk.as_asset());
     }

crates/turbopack/tests/helpers/mod.rs

@@ -6,7 +6,7 @@ pub fn print_changeset(changeset: &Changeset) -> String {
     assert!(changeset.split == "\n");
     let mut result = String::from("--- DIFF ---\n- Expected\n+ Actual\n------------\n");
     const CONTEXT_LINES: usize = 3;
-    let mut context = VecDeque::new();
+    let mut context = VecDeque::with_capacity(CONTEXT_LINES);
     let mut need_context = CONTEXT_LINES;
     let mut has_spacing = false;
     for diff in changeset.diffs.iter() {