Your favorite SWAP Question

[Q4you]

On one our systems we have 20G swap mirrored and with proprity set as follows :

lvol2 8 G Priority : 0
lv_swap1 12 G Priority : 1

If system starts swapping, which will be used first ?

Is there any program or method or utility by which I can bring the system to its knees and start swapping heavy say upto 60 to 80% ??

[James R. Ferguson]

Hi:

The lowest priority (0-10) device (here, 'lvol2') is used first. Device swap is also given preference over filesystem swap. Use 'swapinfo -tam' to monitor swap utilization.

Regards!

...JRF...

[Q4you]

Thanks James,

I am not looking for "swapinfo" to monitor swap space..I am looking for soemthing by which I can surely "cause" heavy swapping temporarily.

[James R. Ferguson]

Hi (again):

I suppose you could write a small C program that does 'malloc()' calls to consume memory.

Regards!

...JRF...

[A. Clay Stephenson]

All priority 0 will be used first; then all 1's ; then 2's .... If devices share an equal priority, swap will be interleaved among them.

All you need to do to get the machine swapping is to launch many processes - assuming nproc/maxuprc is large enough so that you don't hit that limit first. Something as simple as:

#!/usr/bin/sh

I=1
while [[ ${I} -lt 1000 ]]
do
sh &
I=$((${I} + 1))
done

A few of these should bring any box to its knees.

[Shannon Petry]

Just wanted to add that interleaving does NOT occur if all swap priorities are 0, only 1+. If you set all priorities to 0, swap will use a top down approach to filling/using swap.

Regards,
Shannon