Tune the way linux use the swap with the swappiness parameter
Check how the swap is used on your machine:
You can print how the system is using the swap with the vmstat command :
thomas@home:~$ vmstat 2 procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 25192 81956 93052 2383988 0 0 8 15 1 1 1 1 98 0 6 0 25192 71076 93100 2384224 0 0 10 272 1148 1265 8 10 80 2 0 0 25192 97492 93016 2368148 0 0 132 1186 1380 1845 26 35 39 0 0 0 25192 96648 93032 2368740 0 0 70 188 1121 1066 2 2 96 1 0 0 25192 96400 93044 2368976 0 0 0 188 1117 1082 1 1 98 0
the '2' parameter stands for the refresh time in seconds.
si stands for Swap IN (byte written to the swap)
so stands for Swap OUT (byte removed from the swap)
On a server which has enough RAM, I observed that there was regularly swap IN activity.
So that the server use more the RAM and less the swap, we need to tune the swappiness parameter.
By default, on ubuntu, it is set to '60'.
Basically, 0 means do not use the swapp, 100 means use it a lot.
You can check your current system value with this command :
cat /proc/sys/vm/swappiness
You can set it on the fly with the following command :
echo 40 > /proc/sys/vm/swappiness
run vmstat again and see if it changes anything on the swap activity.
On my server, with this parameter, the swap IN activity stopped.
But with this way of setting the swappiness, the parameter value you set won't last after a reboot, it will be reset to default value.
To change definitively the swappiness value, you need to edit the /etc/sysctl.conf
and add the following line at the end of the file :
#swapping tendancy 0 :no swap, 100 : full swapping
vm.swappiness = 40
save your change and then run sysctl like this :
sudo sysctl -p
it should print
vm.swappiness = 40
reboot and recheck the
cat /proc/sys/vm/swappiness
the parameter should have keep the new value.
Recheck vmstat output to see how the situation has evolved.
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