Swap usage on darwin from sysctl vm.swapusage (#1608)

Signed-off-by: jonas <jonas.lindmark@denacode.se>

collector/meminfo_darwin.go

@@ -16,6 +16,8 @@
 package collector
 
 // #include <mach/mach_host.h>
+// #include <sys/sysctl.h>
+// typedef struct xsw_usage xsw_usage_t;
 import "C"
 
 import (
@@ -43,6 +45,13 @@ func (c *meminfoCollector) getMemInfo() (map[string]float64, error) {
 	if err != nil {
 		return nil, err
 	}
+
+	swapraw, err := unix.SysctlRaw("vm.swapusage")
+	if err != nil {
+		return nil, err
+	}
+	swap := (*C.xsw_usage_t)(unsafe.Pointer(&swapraw[0]))
+
 	// Syscall removes terminating NUL which we need to cast to uint64
 	total := binary.LittleEndian.Uint64([]byte(totalb + "\x00"))
 
@@ -59,5 +68,8 @@ func (c *meminfoCollector) getMemInfo() (map[string]float64, error) {
 		"swapped_in_bytes_total":  ps * float64(vmstat.pageins),
 		"swapped_out_bytes_total": ps * float64(vmstat.pageouts),
 		"total_bytes":             float64(total),
+		"swap_used_bytes":         float64(swap.xsu_used),
+		"swap_free_bytes":         float64(swap.xsu_avail),
+		"swap_total_bytes":        float64(swap.xsu_total),
 	}, nil
 }