How does Linux use it's swap file?

[Daniel ~]

I'm asking because it seems to use it rather sparingly...or to be more precise, never.

Yet it's there! Is it only there to facilitate install...just guessing now LOL

I've never seen it any different from what it is now (See pic)

[ThunderRd]

I'm not at my machine right now, but I think that I've got a 1.5G swap partition, and I have never seen Linux use more than 100-200Kb (and that is a rare thing.)

You could easily reduce the size of your swap partition with no ill effects.

Try these links for a bit of information on Linux 'swappiness':

Performance tuning Linux Kernel with swappiness parameter | Linux Poison

https://wiki.archlinux.org/index.php...ng_Performance

[Daniel ~]

Thanks for the hook up, I'll check it out!

It's been to long since I used gedit, can you walk me through this? I'm set at 60 BTW would like to try 10.

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

To check the swappiness value use command: cat /proc/sys/vm/swappiness

To make a change permanent, edit the configuration file with your favorite editor:

vi /etc/sysctl.conf
and add following parameter to the end of the file like so:

vm.swappiness=10

I can't remember how to bring up the config file... so sue me...":O}

[Gizmo]

The swap file is used by Linux when it doesn't have enough physical memory on hand to keep everything in RAM.

With modern operating systems (yes, even windows), applications are launched in a 'virtual' memory space, which basically lets the application pretend that it is running by itself and has all of memory available to it. Of course, this is not actually the case, so there is a memory manager as part of the operating system that 'maps' the virtual space being used by the application (because very, VERY few applications actually use all of the virtual memory space they have access to, but rather only a small portion of it) to the physical memory addresses that are actually available. This mapping typically occurs at the hardware level (with a minimal amount of software assistance) and so normally incurs very little performance overhead.

As you get more and more applications running (or an application begins consuming more and more memory) you eventually get to a point where you can't satisfy the virtual memory request from physical memory any more. At this point, the memory manager has to make a choice; either deny the request outright, or figure out how to free up some memory.

Most applications, even when they have a lot of memory allocated, are typically only actually using a small portion of it at any one time. Since all memory is allocated in units called 'pages', the memory manager can keep track of how recently and how often a particular page of memory is being used. If it needs to free up physical memory, the memory manager goes through the page list and looks for memory that hasn't been recently used. This is where the swap file comes in.

Once the memory manager determines that a page of memory hasn't been used recently (where 'recently' is some arbitrarilly defined threshold that is operating system and version and sometimes even load dependent), that page of memory gets 'swapped out' to the swap file, and some internal markers get updated to let the memory manager know that page has been swapped out.

If at some later point, an application whose memory has been swapped out to disk decides that it needs to access the 'swapped out' memory, the memory manager will go through the process described above to determine what it can free up, and the pull the 'swapped out' memory back in.

For Windows, the 'swap file' is the paging file. On linux, it can either be the swap file or the swap partition (depending on how you set your system up).

Also on Windows, you MUST have a paging file defined; windows gets very pissy if you turn off the paging file, because windows uses the paging file for many things including named pipes and memory mapped files.

On Linux, you can turn off the swap file without any adverse effects (other than once you exhaust physical memory, you are done).

Regardless of operating system, it is possible to run into a situation where you are swapping continously, which thrashes the disk. This happens when your running applications require more actual working data in memory than you have physical memroy to accomodate. Once you get to this state, things start going downhill in a hurry and you can grind your system to a complete halt in short order as your hard drive becomes the system bottleneck.

[Daniel ~]

Thank you gizmo, very clear.!

Say, I've most of my gedit skills back ...like cut and like paste... but I can't seem to remember "save".

If I login I can't reach gedit, when I try to "save as" my changes it says I don't have permission to change this read only file... I CREATED THIS SYSTEM!!!! LOL

[ThunderRd]

You have to run your editor as root to be able to edit sysctl.conf.

try sudo? or gksu? I don't know for sure what Mint uses, but it's prolly sudo

[Daniel ~]

When I su to root gedit won't open, when I don't, it will but I can save, no permission..

[ThunderRd]

gksudo gedit

Then enter your password when it is requested. If that doesn't work, do you have nano or vim installed?

[Daniel ~]

Oh, you one tricky guy ThunderRd! Here it is all "Saved as." and Many thanks!

So this doesn't change the size of the swap file, just how much my install uses it?

[ThunderRd]

Originally Posted by Daniel ~

So this doesn't change the size of the swap file, just how much my install uses it?

Correct, but since it wasn't using it very often to begin with, you most likely won't notice any difference.

Is your swap a file or a partition?

[chrisbard]

What an interesting reading, how very easy it is

[Daniel ~]

Originally Posted by ThunderRd

Correct, but since it wasn't using it very often to begin with, you most likely won't notice any difference.

Is your swap a file or a partition?

It shows up as an 8 gig partition along with 8 gigs of extended space, the rest is all a single volume.

[Daniel ~]

Originally Posted by chrisbard

What an interesting reading, how very easy it is

It really is. just cut and paste, just haven't done anything with terminal in several years... Mint, rarely needs it...

[Gizmo]

Originally Posted by chrisbard

What an interesting reading, how very easy it is

Yeah, rather like editing the registry when you aren't familiar with regedit (or is it regedt32, no wait, I need to use poledit, woops no, that's gpedit...)

[Aedan]

Not sure that comparing Linux from 2012 with Windows from 2000 is really a fair comparison there.

Since the release of Windows XP regedit and regdt32 result in the same code being executed. Additionally gpedit pretty much replaced poledit, as gpedit allows you to edit both the local policy and group policy. Anyhow, you don't have to use gpedit to set group policy - you can use regedit if you desire to have an in-depth knowledge of the registry.

[Daniel ~]

That sounds great,,, how much does it cost again? ":O}

[Aedan]

A bit less than a copy of Red Hat Enterprise Linux for the desktop?

[Daniel ~]

Perhps we should avoid them both! Perhaps each has it's place. ":O}

How have you been A?