diff --git a/cache/file.go b/cache/file.go
index 12982e26..a80f3678 100644
--- a/cache/file.go
+++ b/cache/file.go
@@ -144,12 +144,13 @@ func (this *FileCache) Get(key string) interface{} {
 
 // Put value into file cache.
 // timeout means how long to keep this file, unit of ms.
+// if timeout equals FileCacheEmbedExpiry(default is 0), cache this item forever.
 func (this *FileCache) Put(key string, val interface{}, timeout int64) error {
 	filename := this.getCacheFileName(key)
 	var item FileCacheItem
 	item.Data = val
 	if timeout == FileCacheEmbedExpiry {
-		item.Expired = time.Now().Unix() + (86400 * 365 * 10) //10年
+		item.Expired = time.Now().Unix() + (86400 * 365 * 10) // ten years
 	} else {
 		item.Expired = time.Now().Unix() + timeout
 	}
diff --git a/cache/memory.go b/cache/memory.go
index 839fed72..e1284b79 100644
--- a/cache/memory.go
+++ b/cache/memory.go
@@ -26,7 +26,7 @@ type MemoryCache struct {
 	lock  sync.RWMutex
 	dur   time.Duration
 	items map[string]*MemoryItem
-	Every int // run an expiration check Every cloc; time
+	Every int // run an expiration check Every clock time
 }
 
 // NewMemoryCache returns a new MemoryCache.
@@ -52,6 +52,7 @@ func (bc *MemoryCache) Get(name string) interface{} {
 }
 
 // Put cache to memory.
+// if expired is 0, it will be cleaned by next gc operation ( default gc clock is 1 minute).
 func (bc *MemoryCache) Put(name string, value interface{}, expired int64) error {
 	bc.lock.Lock()
 	defer bc.lock.Unlock()