Novell LINUX ENTERPRISE SERVER 11 - DEPLOYMENT Deployment Manual page 245

the size of your ram in swap, the performance of the system suffered. This does not
hold true anymore as these limitations no longer exist.
Linux uses a page called "Least Recently Used" (LRU) to select pages that might be
moved from memory to disk. Therefore, the running applications have more memory
available and even their caching works more smoothly.
If an application tries to allocate as much memory as it can possibly get, there are some
problems with swap. There are three major cases to look at:
System with no swap
The application gets all memory that can be freed by any means. All caches are
freed, and thus all other applications are slowed down. After a few minutes, the
out of memory killer mechanism of the kernel will become active and kill the pro-
cess.
System with medіum sized swap (128 MB–512 MB)
At first, the system is slowed down like a system without swap. After all physical
ram has been used up, swap space is used as well. At this point, the system becomes
very slow and it becomes impossible to run commands from remote. Depending
on the speed of the hard disks that run the swap space, the system stays in this
condition for about 10 to 15 minutes until the out of memory killer of the kernel
resolves the issue. Note, that you will need a certain amount of swap if the computer
should perform a "suspend to disk". In that case, the swap size should be reasonably
big to contain the necessary data from memory (512 MB–1GB).
System with lots of swap (several GB)
It is better to not have an application that is running wild and swapping frantically,
in this case. If you do have this problem, the system will need many hours to recover.
In the process, it is likely that other processes get timeouts and faults, leaving the
system in an undefined state, even if the faulty process is killed. In this case, reboot
the machine hard and try to get it running again. Lots of swap is only useful if you
have an application that relies on this feature. Such applications (like databases or
graphics manipulation programs) often have an option to directly use hard disk
space for their needs. It is advisable to use this option instead of using lots of swap
space.
If your system does not run wild, but needs more swap after some time, it is possible
to extend the swap space online. If you prepared a partition for swap space, just add
this partition with YaST. If you do not have a partition available, you may also just use
a swap file to extend the swap. Swap files are generally slower than partitions, but
Advanced Disk Setup 233