Linux – Why does mouse and keyboard freeze when Linux swaps

A swap file is more flexible but also more fallible than a swap partition. A filesystem error could damage the swap file. A swap file can be a pain for the administrator, since the file can't be moved or deleted. A swap file can't be used for hibernation. A swap file was slightly slower in the past, though the difference is negligible nowadays.

The advantage of a swap file is not having to decide the size in advance. However, under Linux, you still can't resize a swap file online: you have to unregister it, resize, then reregister (or create a different file and remove the old one). So there isn't that much benefit to a swap file under Linux, compared to a swap partition. It's mainly useful when you temporarily need more virtual memory, rather than as a permanent fixture.

It is normal for Linux systems to use some swap even if there is still RAM free. The Linux kernel will move to swap memory pages that are very seldom used (e.g., the getty instances when you only use X11, and some other inactive daemon).

Swap space usage becomes an issue only when there is not enough RAM available, and the kernel is forced to continuously move memory pages to swap and back to RAM, just to keep applications running. In this case, system monitor applications would show a lot of disk I/O activity.

For comparison, my Ubuntu 10.04 system, with two users logged in with X11 sessions both running GNOME desktop, uses ~600MB of swap and ~1GB of RAM (not counting buffers and fs cache), so I'd say that your figures for swap usage look normal.