Need more swap space?

When I installed Fedora 10 from scratch, I thought that 2GB was probably enough swap space, given that disk access is slow. With only 4GB of RAM, which used to be a lot, as soon as I started using upwards of 6GB, the swap space I had allocated obviously became filled and the program would fail.

Therefore, I am reverting back to the rule of thumb,
"Your swap space should be about twice your RAM size"
which has never failed me.

However, even though I tried, it's a huge pain to make space when you have three hard drives all allocated into a boot partition, a swap partition, and a bunch of LVM partitions, and a logical volume that uses all the LVM space. Is freeing space for a new swap partition possible? Yes. Fast or convenient? No.

Luckily, I discovered that you can use a file in the file system for swap, just as our favourite operating system from Redmond does. I was successful in doing the following on two different machines:

Become the superuser.

$ sudo su

Create a large file of zeros.

# dd if=/dev/zero of=/swapfile1 bs=1024 count=6144k
6291456+0 records in
6291456+0 records out
6442450944 bytes (6.4 GB) copied, 106.946 s, 60.2 MB/s

Make this file a swap partition.

# mkswap -c /swapfile1
Setting up swapspace version 1, size = 6291452 KiB
no label, UUID=7f5ab06e-4315-4185-b5a2-b3151a5a608c

Add the partition to the swap space.

# swapon /swapfile1

Check that it worked; total swap should be 6GB larger now.

# free -m
          total       used       free     shared    buffers     cached
Mem:          3967       3936         30          0         75       3054
-/+ buffers/cache:        807       3159
Swap:         8144          0       8144

Add the swapon command somewhere in this file. This will add the file to the swap space the at boot.

# vi /etc/rc.local

You're done! However, a partition would be faster (and perhaps safer), so the next time you upgrade, consider re-partitioning.

Also note that Linux will use the partition swap first, as per its priority according to:

# cat /proc/swaps
Filename    Type  Size Used Priority
/dev/sdb1                               partition 2048248 96 -1
/swapfile1                              file  6291448 0 -2

And with that in mind, I can think of all sorts of other fixes for running out of swap space (USB drives, compact flash to SATA adapters, etc.).