diff --git a/mem/mem.go b/mem/mem.go
index 6eb8cf7..fd8337a 100644
--- a/mem/mem.go
+++ b/mem/mem.go
@@ -45,6 +45,7 @@ type VirtualMemoryStat struct {
 	// Linux specific numbers
 	// https://www.centos.org/docs/5/html/5.1/Deployment_Guide/s2-proc-meminfo.html
 	// https://www.kernel.org/doc/Documentation/filesystems/proc.txt
+	// https://www.kernel.org/doc/Documentation/vm/overcommit-accounting
 	Buffers      uint64 `json:"buffers"`
 	Cached       uint64 `json:"cached"`
 	Writeback    uint64 `json:"writeback"`