diff --git a/content/Frontend/React/useWhatsChanged.md b/content/Frontend/React/useWhatsChanged.md
new file mode 100644
index 0000000..f48f473
--- /dev/null
+++ b/content/Frontend/React/useWhatsChanged.md
@@ -0,0 +1,30 @@
+```typescript
+import { useEffect, useRef } from 'react';
+
+/** Pass dictionary of `props` as argument and it will
+ * tell you, which one changed after rerender.
+ * Use `prefix` to distinguish props of different components.
+ */
+// eslint-disable-next-line import/no-unused-modules
+export const useWhatsChanged = (
+  props: Record<string, unknown>,
+  prefix = '',
+) => {
+  const prevProps = useRef(props);
+
+  useEffect(() => {
+    Object.entries(props).forEach(([key, value]) => {
+      if (
+        !Object.prototype.hasOwnProperty.call(prevProps.current, key) ||
+        prevProps.current[key] !== value
+      ) {
+        // eslint-disable-next-line no-console
+        console.log(`${prefix} ${key} has changed`);
+      }
+    });
+
+    prevProps.current = props;
+  }, [props, prefix]);
+};
+
+```
\ No newline at end of file
diff --git a/content/Linux/Find out who uses swap.md b/content/Linux/Find out who uses swap.md
new file mode 100644
index 0000000..6da2737
--- /dev/null
+++ b/content/Linux/Find out who uses swap.md	
@@ -0,0 +1,3 @@
+```shell
+for file in /proc/*/status ; do awk '/VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file; done | sort -k 2 -n -r | less
+```