disk-cache: disable state check when writeback enabled

pkg/chunk/disk_cache.go

@@ -130,7 +130,11 @@ func newCacheStore(m *cacheManagerMetrics, dir string, cacheSize int64, pendingP
 		opTs:          make(map[time.Duration]func() error),
 	}
 	c.stateLock = sync.Mutex{}
-	c.state = newDCState(dcNormal, c)
+	if config.Writeback {
+		c.state = newDCState(dcUnchanged, c)
+	} else {
+		c.state = newDCState(dcNormal, c)
+	}
 
 	c.createDir(c.dir)
 	br, fr := c.curFreeRatio()

pkg/chunk/disk_cache_state.go

@@ -46,17 +46,19 @@ var (
 )
 
 var diskStateNames = map[int]string{
-	dcUnknown:  "unknown",
-	dcNormal:   "normal",
-	dcUnstable: "unstable",
-	dcDown:     "down",
+	dcUnknown:   "unknown",
+	dcNormal:    "normal",
+	dcUnstable:  "unstable",
+	dcDown:      "down",
+	dcUnchanged: "unchanged",
 }
 
 const (
 	dcUnknown = iota
 	dcNormal
 	dcUnstable
 	dcDown
+	dcUnchanged
 )
 
 const (
@@ -93,6 +95,8 @@ func newDCState(state int, cs *cacheStore) dcState {
 		s = &unstableDC{}
 	case dcDown:
 		s = &downDC{}
+	case dcUnchanged:
+		s = &unchangedDC{}
 	}
 	s.init(cs)
 	s.tick()
@@ -115,6 +119,12 @@ func (dc *baseDC) checkCacheOp() error { return nil }
 func (dc *baseDC) beforeCacheOp()      {}
 func (dc *baseDC) afterCacheOp()       {}
 
+type unchangedDC struct {
+	baseDC
+}
+
+func (dc *unchangedDC) state() int { return dcUnchanged }
+
 type normalDC struct {
 	baseDC
 	ioErrCnt uint32