diff --git a/internal/resourcecontrol/resource_control.go b/internal/resourcecontrol/resource_control.go
index 4a98ac2368..6bd67c5496 100644
--- a/internal/resourcecontrol/resource_control.go
+++ b/internal/resourcecontrol/resource_control.go
@@ -16,7 +16,6 @@ package resourcecontrol
 
 import (
 	"reflect"
-	"unsafe"
 
 	"github.com/pingcap/kvproto/pkg/coprocessor"
 	"github.com/pingcap/kvproto/pkg/kvrpcpb"
@@ -43,9 +42,17 @@ func MakeRequestInfo(req *tikvrpc.Request) *RequestInfo {
 	var writeBytes int64
 	switch r := req.Req.(type) {
 	case *kvrpcpb.PrewriteRequest:
-		writeBytes += int64(r.TxnSize)
+		for _, m := range r.Mutations {
+			writeBytes += int64(len(m.Key)) + int64(len(m.Value))
+		}
+		writeBytes += int64(len(r.PrimaryLock))
+		for _, l := range r.Secondaries {
+			writeBytes += int64(len(l))
+		}
 	case *kvrpcpb.CommitRequest:
-		writeBytes += int64(unsafe.Sizeof(r.Keys))
+		for _, k := range r.Keys {
+			writeBytes += int64(len(k))
+		}
 	}
 
 	return &RequestInfo{writeBytes: writeBytes}