Importance of Swap Partition
Solution 1:
The swap partition serves a couple of purposes.
It serves as 'backup' RAM. That is, should your computer run out of RAM, it will use the swap area as a temporary source of more memory. More specifically, it will 'swap' unused items from the RAM into the swap area in order to leave spare space for the applications that need it at that instant. This is not ideal as the data transfer rate to the hard drive is significantly lower than that to your normal RAM. In practice this means its much slower to retrieve information from the swap area.
It is used when the computer hibernates. Hibernation involves taking an image of the RAM in its current state (like an ISO represents an image), and saves it to the swap area. It then reloads this image when the computer restarts.
To be most useful, the swap area should be at least (RAM * 1.5) although more is recommended. For example, on my system with 3gb of RAM, I have a swap area of 7.2gb.
Solution 2:
This is very close to the same as this question about the “right” size for a swap partition. Much of the same information from my answer there applies - basically, if you want to hibernate you generally want your swap space to be at least as big as your RAM, and other than that a round number like 1 or 2 GB is easily sufficient. Because swap is so much slower than RAM, if you're filling up multiple gigabytes of swap your computer has almost certainly become unusably slow.
There's also no real need for a swap partition - swap files (available on the mainstream linux filesystems) give the same performance and make it trivially easy to add more swap space if you decide you haven't got enough.
Solution 3:
here a very deep information about swap
some people say the double of your ram but personally i recommend this :
swap = 1.5 X Total Ram
Example :
if you have 2Gb of ram -> swap = 1.5 x 2 = 3
P.D : Ubuntu Desktop uses Swap to Hibernate (PC off, no power needed, program states saved). If Hibernation is important to you, have more swap space then ram + swap overflow.
Solution 4:
The free command can tell you how much swap you are using. For example on this machine:
$ free -m
total used free buffers cached
Mem: 1947 1863 84 312 758
-/+ buffers/cache: 792 1154
Swap: 4000 3 3997
shows me that I have 2GB (1947m) RAM and that the system has used most of it. However, 312m is used for I/O buffers and the remainder (758m) the system has decided to fill with disk cache.
The disk cache is interesting because it is using fast memory instead of slow disk for its contents. The contents could be gotten from disk, but they are kept around in case they are needed. This also means that there is 758m of memory that can be reclaimed in an instant if necessary because the system knows it can find that data on the disk instead.
That is why there is a second line showing that if there were no buffering and cache, I'd have half my RAM (1154m) available for use.
The third line shows that I have an overly large swap partition (it was there and wasn't doing anything) of which a whopping 3m have been used. This is stuff that the kernel really doesn't expect to have to use anytime soon so it was stuck out on the "back porch".
While free gives you the snapshot now, vmstat can give you a running picture:
$ vmstat 10
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 3588 86236 316524 769132 0 0 14 13 126 81 4 1 95 0
0 0 3588 83872 316532 770512 0 0 0 20 264 1229 3 1 96 0
There's a lot of information there, but of interest is that there is no swap-in (si) or swap-out (so) traffic. Which means I'm not using the swap at all over the last 10 seconds.