Merge release-20210503.0-47-g07e32fa69 (automated)

3 files changed, 24 insertions, 0 deletions

diff --git a/pkg/sentry/socket/unix/socket_refs.go b/pkg/sentry/socket/unix/socket_refs.go
index 2a7fcb253..6a76efe24 100644
--- a/pkg/sentry/socket/unix/socket_refs.go
+++ b/pkg/sentry/socket/unix/socket_refs.go
@@ -20,6 +20,14 @@ var socketOperationsobj *SocketOperations
 // Refs implements refs.RefCounter. It keeps a reference count using atomic
 // operations and calls the destructor when the count reaches zero.
 //
+// NOTE: Do not introduce additional fields to the Refs struct. It is used by
+// many filesystem objects, and we want to keep it as small as possible (i.e.,
+// the same size as using an int64 directly) to avoid taking up extra cache
+// space. In general, this template should not be extended at the cost of
+// performance. If it does not offer enough flexibility for a particular object
+// (example: b/187877947), we should implement the RefCounter/CheckedObject
+// interfaces manually.
+//
 // +stateify savable
 type socketOperationsRefs struct {
 	// refCount is composed of two fields:
diff --git a/pkg/sentry/socket/unix/socket_vfs2_refs.go b/pkg/sentry/socket/unix/socket_vfs2_refs.go
index f10033260..fe05721cf 100644
--- a/pkg/sentry/socket/unix/socket_vfs2_refs.go
+++ b/pkg/sentry/socket/unix/socket_vfs2_refs.go
@@ -20,6 +20,14 @@ var socketVFS2obj *SocketVFS2
 // Refs implements refs.RefCounter. It keeps a reference count using atomic
 // operations and calls the destructor when the count reaches zero.
 //
+// NOTE: Do not introduce additional fields to the Refs struct. It is used by
+// many filesystem objects, and we want to keep it as small as possible (i.e.,
+// the same size as using an int64 directly) to avoid taking up extra cache
+// space. In general, this template should not be extended at the cost of
+// performance. If it does not offer enough flexibility for a particular object
+// (example: b/187877947), we should implement the RefCounter/CheckedObject
+// interfaces manually.
+//
 // +stateify savable
 type socketVFS2Refs struct {
 	// refCount is composed of two fields:
diff --git a/pkg/sentry/socket/unix/transport/queue_refs.go b/pkg/sentry/socket/unix/transport/queue_refs.go
index 42c5b7ce0..0db027c09 100644
--- a/pkg/sentry/socket/unix/transport/queue_refs.go
+++ b/pkg/sentry/socket/unix/transport/queue_refs.go
@@ -20,6 +20,14 @@ var queueobj *queue
 // Refs implements refs.RefCounter. It keeps a reference count using atomic
 // operations and calls the destructor when the count reaches zero.
 //
+// NOTE: Do not introduce additional fields to the Refs struct. It is used by
+// many filesystem objects, and we want to keep it as small as possible (i.e.,
+// the same size as using an int64 directly) to avoid taking up extra cache
+// space. In general, this template should not be extended at the cost of
+// performance. If it does not offer enough flexibility for a particular object
+// (example: b/187877947), we should implement the RefCounter/CheckedObject
+// interfaces manually.
+//
 // +stateify savable
 type queueRefs struct {
 	// refCount is composed of two fields: