CentOS - Jun 2006 - Postpone/avoid swaping while there is still free RAM.

Hi people,

I got Centos 4.3 on a 1GB Pentium IV machine. The output of free

-------------------
$ free
             total       used       free     shared    buffers     cached
Mem:       1026896     573848     453048          0       2988     131712
-/+ buffers/cache:     439148     587748
Swap:      1052248     137568     914680
------------------

There is plenty of free ram, but the kernel prefers to swap unused
pages to disk. And later I have to wait for them to be unswapped, the
Desktop looses its promptness - annoying.

In win2k and winXP there is a registry key property which prevents
swapping while there is still RAM.

Do you know whether I can achieve the same in linux?

Best regards!
alex

-----------------
>
> There is plenty of free ram, but the kernel prefers to swap unused
> pages to disk. And later I have to wait for them to be unswapped, the
> Desktop looses its promptness - annoying.
This is a bug in the -34 and -34.0.1 kernels and possibly 1 or 2
before that. Systems under load swap prematurely. You can install the
test kernel from the dev tree which will be in the upcoming 4.4
release. Your issue is fixed in that kernel.

You may also want to set 'vm.swappiness = 10'  or so in
/etc/sysctl.conf (reread without rebooting with sysctl -p)

The lower the number (0-100) you set for swappiness, the less willing
your system will be to swap. No setting it to 0 will not keep your
system from swapping at all.
> In win2k and winXP there is a registry key property which prevents
> swapping while there is still RAM.
>
> Do you know whether I can achieve the same in linux?


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Alexander Georgiev wrote:
> 
> There is plenty of free ram, but the kernel prefers to swap unused
> pages to disk. And later I have to wait for them to be unswapped, the
> Desktop looses its promptness - annoying.
> 
> In win2k and winXP there is a registry key property which prevents
> swapping while there is still RAM.
> 
> Do you know whether I can achieve the same in linux?
There has been a huge thread concerning this -- maybe even in this list.
 Use google and look for "swappiness".

The place to make the change (temporarily) is:

/proc/sys/vm/swappiness

To make it permanent, change /etc/sysctl.conf

Barry