perf: introduce size hint for storage key and value (#695)

foyer-common/src/code.rs

@@ -25,13 +25,23 @@ impl<T: Send + Sync + 'static + std::hash::Hash + Eq> Key for T {}
 impl<T: Send + Sync + 'static> Value for T {}
 
 /// Key trait for the disk cache.
-pub trait StorageKey: Key + Serialize + DeserializeOwned {}
-impl<T> StorageKey for T where T: Key + Serialize + DeserializeOwned {}
+pub trait StorageKey: Key + Serialize + DeserializeOwned + Hint {}
+impl<T> StorageKey for T where T: Key + Serialize + DeserializeOwned + Hint {}
 
 /// Value trait for the disk cache.
-pub trait StorageValue: Value + 'static + Serialize + DeserializeOwned {}
-impl<T> StorageValue for T where T: Value + Serialize + DeserializeOwned {}
+pub trait StorageValue: Value + 'static + Serialize + DeserializeOwned + Hint {}
+impl<T> StorageValue for T where T: Value + Serialize + DeserializeOwned + Hint {}
 
 /// Hash builder trait.
 pub trait HashBuilder: BuildHasher + Send + Sync + 'static {}
 impl<T> HashBuilder for T where T: BuildHasher + Send + Sync + 'static {}
+
+/// Hint functions collection.
+pub trait Hint {
+    /// Size hint for serialization.
+    fn serialized_size_hint(&self) -> usize {
+        0
+    }
+}
+
+impl<T: Send + Sync + 'static> Hint for T {}

foyer-storage/src/serde.rs

@@ -94,6 +94,17 @@ impl EntrySerializer {
 
         Ok(KvInfo { key_len, value_len })
     }
+
+    pub fn size_hint<'a, K, V>(key: &'a K, value: &'a V, compression: &'a Compression) -> usize
+    where
+        K: StorageKey,
+        V: StorageValue,
+    {
+        match compression {
+            Compression::Zstd | Compression::Lz4 => 0,
+            Compression::None => key.serialized_size_hint() + value.serialized_size_hint(),
+        }
+    }
 }
 
 #[derive(Debug)]

foyer-storage/src/store.rs

@@ -144,7 +144,8 @@ where
 
         self.inner.write_runtime_handle.spawn(async move {
             if force || this.pick(entry.key()) {
-                let mut buffer = IoBytesMut::new();
+                let mut buffer =
+                    IoBytesMut::with_capacity(EntrySerializer::size_hint(entry.key(), entry.value(), &compression));
                 match EntrySerializer::serialize(
                     entry.key(),
                     entry.value(),