rc: implement core/memstats to print internal memory usage info

fs/rc/internal.go

@@ -4,6 +4,7 @@ package rc
 
 import (
 	"os"
+	"runtime"
 
 	"github.com/pkg/errors"
 )
@@ -42,6 +43,22 @@ the commands response.`,
 This returns PID of current process.
 Useful for stopping rclone process.`,
 	})
+	Add(Call{
+		Path:  "core/memstats",
+		Fn:    rcMemStats,
+		Title: "Returns the memory statistics of the running program",
+		Help: `
+This returns the memory statistics of the running program.  What the values mean
+are explained in the go docs: https://golang.org/pkg/runtime/#MemStats
+
+The most interesting values for most people are:
+
+* HeapAlloc: This is the amount of memory rclone is actually using
+* HeapSys: This is the amount of memory rclone has obtained from the OS
+* Sys: this is the total amount of memory requested from the OS
+  * It is virtual memory so may include unused memory
+`,
+	})
 }
 
 // Echo the input to the ouput parameters
@@ -67,3 +84,31 @@ func rcPid(in Params) (out Params, err error) {
 	out["pid"] = os.Getpid()
 	return out, nil
 }
+
+// Return the memory statistics
+func rcMemStats(in Params) (out Params, err error) {
+	out = make(Params)
+	var m runtime.MemStats
+	runtime.ReadMemStats(&m)
+	out["Alloc"] = m.Alloc
+	out["TotalAlloc"] = m.TotalAlloc
+	out["Sys"] = m.Sys
+	out["Mallocs"] = m.Mallocs
+	out["Frees"] = m.Frees
+	out["HeapAlloc"] = m.HeapAlloc
+	out["HeapSys"] = m.HeapSys
+	out["HeapIdle"] = m.HeapIdle
+	out["HeapInuse"] = m.HeapInuse
+	out["HeapReleased"] = m.HeapReleased
+	out["HeapObjects"] = m.HeapObjects
+	out["StackInuse"] = m.StackInuse
+	out["StackSys"] = m.StackSys
+	out["MSpanInuse"] = m.MSpanInuse
+	out["MSpanSys"] = m.MSpanSys
+	out["MCacheInuse"] = m.MCacheInuse
+	out["MCacheSys"] = m.MCacheSys
+	out["BuckHashSys"] = m.BuckHashSys
+	out["GCSys"] = m.GCSys
+	out["OtherSys"] = m.OtherSys
+	return out, nil
+}