Swap

Linux employs a virtual memory system that allows it to function as if it had more memory than it physically has. Overcommiting functions two ways:

• Programs (such as ones that have child processes that they inherit from parent using COW) don't always use all allocated memory.
• Less active memory regions are moved to disk when memory becomes low on the system.

Swapping is usually done on dedicated partitions or files. The recommended swap size is the total RAM on the system. The kernel memory is never swapped out.

We can see how much swap area the system is using:

cat /proc/swaps

free -m

Other commands:

# format swap partition/file
mkswap

# activate swap partition/file
swapon

# deactivate swap partition/file
swapoff

Full procedure to create add swap:

# Create fs
dd if=/dev/zero of=swpfile bs=1M count=1024

# change ownership of `swpfile# to root
sudo chown root:root swpfile

# activate swap
sudo swapon swpfile

# check it exists
cat /proc/swapfile
Filename    Type  Size Used Priority
/home/app/lfs201/fs/swpfile         file  1048572 512 -2

# deactivate and remove swap
sudo swapoff swpfile
sudo rm swpfile