Ubuntu – Change swap memory size after adding RAM

10.10memoryramswap

I ordered some addon RAM a few days ago to install on my Ubuntu 10.10 stationary computer and while giving it some thought, I remember that I previously did change the SWAP memory file size on a XP computer after doing a RAM upgrade in the past.

Should I change the SWAP memory size (increase?) after installing more RAM into my computer?

Best Answer

The swap partition is used to

move temporarily running programs that are not active,so that to make space for the programs being used.
for hibernation, where your entire RAM is copied to the swap partition.

Therefore, if you will be using hibernation, you should have a swap at least as big as your RAM, and a bit more just in case.

A rule of thumb is to make a swap partition as big as twice your RAM but not go over 3GB (because you will be wasting space).

It is OK to create a second swap partition and have them both active. Linux uses them as if they were a continuous swap partition, so it is fine.

Typically, if you have over 3GB of RAM, then you will notice that Ubuntu will not have a use of your swap. Run the free command and notice the value for Swap: + used. In most cases it just stays to 0.

Related Solutions

Ubuntu – Swap shoots to 100% after a couple of hours of usage

How do I configure swappiness?

The Linux kernel provides a tweakable set ting that controls how often the swap file is used, called swappiness

A swappiness setting of zero means that the disk will be avoided unless absolutely necessary (you run out of memory), while a swappiness setting of 100 means that programs will be swapped to disk almost instantly.

Ubuntu system comes with a default of 60, meaning that the swap file will be used fairly often if the memory usage is around half of my RAM. You can check your own system's swappiness value by running:

one@onezero:~$ cat /proc/sys/vm/swappiness
60

As I have 4 GB of RAM, so I'd like to turn that down to 10 or 15. The swap file will then only be used when my RAM usage is around 80 or 90 percent. To change the system swappiness value, open /etc/sysctl.conf as root. Then, change or add this line to the file:

vm.swappiness = 10

Reboot for the change to take effect

You can also change the value while your system is still running

sysctl vm.swappiness=10

you can also clear your swap by running swapoff -a and then swapon -a as root instead of rebooting to achieve the same effect.

To calculate your swap Formula

free -m (total) / 100 = A

A * 10

root@onezero:/home/one# free -m
             total       used       free     shared    buffers     cached
Mem:          3950       2262       1687          0        407        952
-/+ buffers/cache:        903       3047
Swap:         1953          0       1953

so total is 3950 / 100 = 39.5 * 10 = 395

so what it mean is that when 10 % 395 MB of ram left then it start using swapiness

Help . Ubuntu . Swap

What is swappiness

The swappiness parameter controls the tendency of the kernel to move processes out of physical memory and onto the swap disk. Because disks are much slower than RAM, this can lead to slower response times for system and applications if processes are too aggressively moved out of memory.

. swappiness can have a value of between 0 and 100

. swappiness=0 tells the kernel to avoid swapping processes out of physical memory for as long as possible

. swappiness=100 tells the kernel to aggressively swap processes out of physical memory and move them to swap cache

The default setting in Ubuntu is swappiness=60. Reducing the default value of swappiness will probably improve overall performance for a typical Ubuntu desktop installation. A value of swappiness=10 is recommended, but feel free to experiment.

Started Using swap at 91%

enter image description here As i have configured my system & vm to make use of ram at 90 % . At 90 % there was no swapping

after that i opened some application like Firefox & Shutter , its start swapping because of ram usage is above 90 %

Ubuntu – Why does the system use so much cache

You probably need to reduce your swappiness.

The kernel considers it better to use the free ram as cache rather then evict cache pages and have the ram marked as truly free. Growing the cache is generally a good thing.

Now the question arises what to do when all the memory is allocated to cache and your application needs more memory. Often the right thing to do is to evict a page from the cache and hand it over to your app but occasionally it is beneficial to swap out a rarely used page, give that to your app and keep the cache intact.

This process is loosely controlled by /proc/sys/vm/swappiness. For more information please check the excellent answers to Why most people recommend to reduce swappiness to 10-20? and How do I configure swappiness?.