rc: add core/gc to run a garbage collection on demand

docs/content/rc.md

@@ -97,6 +97,12 @@ Eg
 The format of the parameter is exactly the same as passed to --bwlimit
 except only one bandwidth may be specified.
 
+### core/gc: Runs a garbage collection.
+
+This tells the go runtime to do a garbage collection run.  It isn't
+necessary to call this normally, but it can be useful for debugging
+memory problems.
+
 ### core/memstats: Returns the memory statistics
 
 This returns the memory statistics of the running program.  What the values mean

fs/rc/internal.go

@@ -57,6 +57,16 @@ The most interesting values for most people are:
 * 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
+`,
+	})
+	Add(Call{
+		Path:  "core/gc",
+		Fn:    rcGc,
+		Title: "Runs a garbage collection.",
+		Help: `
+This tells the go runtime to do a garbage collection run.  It isn't
+necessary to call this normally, but it can be useful for debugging
+memory problems.
 `,
 	})
 }
@@ -112,3 +122,10 @@ func rcMemStats(in Params) (out Params, err error) {
 	out["OtherSys"] = m.OtherSys
 	return out, nil
 }
+
+// Do a garbage collection run
+func rcGc(in Params) (out Params, err error) {
+	out = make(Params)
+	runtime.GC()
+	return out, nil
+}