Swapping¶
Backing store¶
- A chunk of disk separated from file system
# While installing arch linux, if you want to enable swap, which you should, you have to do
mkswap /dev/sdXy
swapon /dev/sdXy
# so that the system knows you want to make the partition /dev/sdXy the swap space
# Clearly, this is separated from the file system.
Why?¶
Because
- Swap lower priority process with a higher one
Note
- A process to be swapped must be idle, or the io device will write to memory, and the image is then broken on disk
- IO operations are done through OS buffers (a memory space belongs to no user processes)
Bottleneck¶
- The bottleneck is the transfer time, because disk is slow
How to swap efficiently?