from the research department - ramster in Linux 3.4 staging drivers
By wcoekaer on May 26, 2012
It's a long road to getting all these stars aligned but we are very close now in terms of Linux kernel features to help with this. Over the last few years Dan Magenheimer has been working hard on what's called transcendent memory, a collection of features that include cleancache, frontswap and ramster. Now with Linux 3.4, we have tmem, cleancache and ramster in kernel upstream. Frontswap is still pending but we're working on it.
As a refresher, you can read more about cleancache in this writeup I did just bout a year ago. Frontswap is more tricky, because here we can use transcendent memory as a swap device. Pages swapped out cannot just disappear, they have to be persistent until the OS decides to no longer need them. In other words, with cleancache we provide extra memory(extra cache) but with the understanding that that extra memory might just disappear. With frontswap, we provide swap space through the same mechanism, with the understanding that it's not going to just disappear. One place where frontswap is different from regular swap, is its size. A swapdevice is pre-created with a specific size, a file acting as a swap device or a physical/logical volume. They do not grow or shrink dynamically. frontswap is more dynamic. The advantage of frontswap is that you can use ram on a remote server or in the hypervisor as very fast storage. It can also do compression of memory pages using zcache.
Looking forward to frontswap getting into the kernel and many of these features get into customers hands through the Unbreakable Enterprise Kernel and as products evolve and features get management also into Oracle VM.