Memory and swap management¶
Inspecting and tuning ram¶
Free memory¶
$ free -m
output:
total used free shared buffers cached
Mem: 2003 1618 385 0 136 592
-/+ buffers/cache: 889 1113
Swap: 2047 0 2047
It means you have 2G ram 1.6G are used 889M actively by applications and 728M can be reclaimed 136M from buffers and 592M from cached data; the total amount of space that could be used is 1.1G
2G of swap are unused.
You can find more explanations in Linux ate my ram and in Tips for Optimizing Linux Memory Usage.
A very good ref is also Tuning the Memory Management Subsystem. chapter 15 of openSUSE System Analysis and Tuning Guide.
Managing swap space¶
Swap Info¶
$ swapon -s
The output is:
Filename Type Size Used Priority
/dev/mapper/vg-swap partition 2097148 0 -1
or free -m
Swap partition¶
$ mkswap /dev/mapper/vg-swap
$ swapon /dev/mapper/vg-swap
In fstab:
/dev/mapper/vg-swap none swap sw 0 0
Swap file¶
$ dd if=/dev/zero of=/swapfile bs=1M count=512
if the file system is ext4 or brtfs but not ext2/3 you can also use the quicker:
$ fallocate -l 512M /swapfile
Then:
$ chmod 600 /swapfile
$ mkswap /swapfile
$ swapon /swapfile
/swapfile none swap defaults 0 0
Swappiness¶
A low value of kernel swappiness parameter will reduce swapping from RAM, default is 60 and current value is:
$ cat /proc/sys/vm/swappiness
To test swapiness:
$ echo 5 > /proc/sys/vm/swappiness
To set it at boot put in /etc/sysctl.conf:
vm.swappiness = 5