If you check the output of the swapon -s command, you would see the Priority column. The priority column defines the order in which the swap devices are used when required. In our example below the priority -1 is higher than the priority -2 (as the values are in negative).
# swapon -s Filename Type Size Used Priority /dev/dm-1 partition 268435452 0 -1 /swapfile file 102396 0 -2
By default when the priorities are assigned as the swap devices are created and added as swap. But we can also change the priority of the devices.
Temporarily change the swap priority
1. Before changing the priority make sure the swap device is not in use by the system.
# free
total used free shared buff/cache available
Mem: 263847032 4561048 214238864 324524 45047120 257755920
Swap: 268537848 0 268537848
As seen in the output above, 0 MB of swap is being used currently.
2. Disable the swap devices
# swapoff /swapfile # swapoff /dev/dm-1 # swapon -s Filename Type Size Used Priority /dev/dm-1 partition 268435452 0 -1
3. set the priority of the swap device /swapfile as 5 which higher than the priority of the other swap device(-1).
# swapon -p 5 /swapfile # swapon -s Filename Type Size Used Priority /dev/dm-1 partition 268435452 0 -1 /swapfile file 102396 0 5
Persistently change the swap priority
To change the priority of swap device permanently, we have to edit the /etc/fstab file accordingly.
1. First, take the backup of /etc/fstab file.
# cp -p /etc/fstab /etc/fstba_orig
2. Modify the swap device priority of /swapfile to 5 from -2.
# vi /etc/fstab /dev/mapper/vg_os-lv_swap swap swap defaults 0 0 /swapfile swap swap pri=9 0 0