expose page cache size

container/libcontainer/helpers.go

@@ -378,6 +378,7 @@ func toContainerStats1(s *cgroups.Stats, ret *info.ContainerStats) {
 func toContainerStats2(s *cgroups.Stats, ret *info.ContainerStats) {
 	ret.Memory.Usage = s.MemoryStats.Usage.Usage
 	ret.Memory.Failcnt = s.MemoryStats.Usage.Failcnt
+	ret.Memory.Cache = s.MemoryStats.Stats["cache"]
 	ret.Memory.RSS = s.MemoryStats.Stats["rss"]
 	if v, ok := s.MemoryStats.Stats["pgfault"]; ok {
 		ret.Memory.ContainerData.Pgfault = v

info/v1/container.go

@@ -308,6 +308,10 @@ type MemoryStats struct {
 	// Units: Bytes.
 	Usage uint64 `json:"usage"`
 
+	// Number of bytes of page cache memory.
+	// Units: Bytes.
+	Cache uint64 `json:"cache"`
+
 	// The amount of anonymous and swap cache memory (includes transparent
 	// hugepages).
 	// Units: Bytes.

metrics/prometheus.go

@@ -127,6 +127,13 @@ func NewPrometheusCollector(infoProvider infoProvider, f ContainerNameToLabelsFu
 					}
 					return values
 				},
+			}, {
+				name:      "container_memory_cache",
+				help:      "Number of bytes of page cache memory.",
+				valueType: prometheus.GaugeValue,
+				getValues: func(s *info.ContainerStats) metricValues {
+					return metricValues{{value: float64(s.Memory.Cache)}}
+				},
 			}, {
 				name:      "container_memory_rss",
 				help:      "Size of RSS in bytes",