Builtin RAM disk

The io-blk module supports an internal RAM-disk device that can be created via a command-line option (blk ramdisk=size).

Since this RAM disk is internal to the io-blk module (rather than created and maintained by an additional device driver such as devb-ram), performance is significantly better than that of a dedicated RAM-disk driver.

By incorporating the RAM-disk device directly at the io-blk layer, the device's data memory parallels the main cache, so I/O operations to this device can bypass the buffer cache, eliminating a memory copy yet still retaining coherency. Contrast this with a driver-level implementation (e.g., devb-ram) where transparently presenting the RAM as a block device involves additional memory copies and duplicates data in the buffer cache. Inter-DLL callouts are also eliminated. In addition, there are benefits in terms of installation footprint for systems that have a hard disk and also want a RAM disk: only the single driver is needed.