Modern operating systems use much of their available memory as a page cache, keeping binaries, data, and libraries in memory in order to avoid accesses to slow disks. At the same time, rebooting a machine is one of the best ways to start with a clean slate, by resetting memory leaks, configuration mismatches, and stale performance. Traditionally, a reboot also clears the page cache, which takes many minutes to repopulate.

Kourai addresses this challenge by retaining the page cache across reboots. He uses the virtual machine monitor (VMM) to watch for clean and dirty page cache entries. Upon reboot, clean page cache entries are retained while dirty pages are thrown away. This results in much faster recovery after a reboot, which can be critical for many Web servers or database systems.

Read this if you are interested in virtual machines. The author’s use of the VMM as a page cache monitor is innovative, and addresses the mismatch between disk speeds and main memory.