Comments on: Why swap on Linux is always good, even with tons of RAM

By: What’s in a SWAP? « Sanity, Insanity, and Moi

What’s in a SWAP? « Sanity, Insanity, and Moi — Wed, 22 Aug 2007 05:33:29 +0000

[...] Why swap on Linux is always good, even with tons of RAM [...]

By: Rudd-O

Rudd-O — Thu, 19 Jan 2006 21:15:48 +0000

If you have a gigabyte of RAM, and swap is never touched on your system, then you might as well disable the swap. Just remember to reenable it when you're going to start memory-hungry applications...

...oh wait, why should you need to manually enable and disable swap, when leaving it on all the time has the same effect, plus you don't need to intervene at all?

(that was a bit tongue-in-cheek)

By: Rudd-O

Rudd-O — Thu, 19 Jan 2006 21:14:10 +0000

Using RAM as a swap space would be extremely dumb, since the whole point of swap is to MAKE ROOM in fast RAM for cache, shared libraries and applications.

In other words, swap is used to simulate RAM. What do you gain from using a part of your RAM as swap? Nothing!

By: Renan

Renan — Thu, 19 Jan 2006 18:38:50 +0000

I have 512MB RAM, and never felt the need for much swap, except when I’m running a memory intensive application like Mathematica, SCILAB, editing large images with GIMP or running VMware. Usually runs with ~350MB free RAM.

By: NA

NA — Thu, 19 Jan 2006 11:18:30 +0000

For linux kernel 2.6.x you have setting in /proc/sys/vm/swappiness, telling the kernel how aggressive it should be regarding swapping. The default value on fedora this value is 60. Higher value means more swapping (I think the value ranges from 0 to 100).

On my desktop machine I use the command "echo 100 > /proc/sys/vm/swappiness" as root to tell the kernel to be very aggressive with swapping. This means that the kernel will swap out many unneeded "pages" from memory and instead use the memory for caching as described in the article. So on my machine the swap usage is high, but so is the memory usage for cache. A lower value means that the kernel will not try to swap as much to free memory for cache. Just try with different values here, since you can change this value runtime as shown above..

By: Gabor

Gabor — Thu, 19 Jan 2006 09:35:38 +0000

Is it possible to create a swap partition in the memory? I mean a virtual file system in the memory used as swap partition. It would use a very fast media and still the computer would have swap.

By: Davepet

Davepet — Thu, 19 Jan 2006 08:16:48 +0000

If all this is true, I'd like to know, then why my machine, with 1GB of RAM & a half GB of swap, never shows any swap being used? Not ever.

I'm currently running with 630 MB of RAM used & no swap. 97 processes running.

Seem to me that unless you are doing video editing or have multiple memory hog apps open, that swap isn't important with a gig of RAM.

Dave

By: Rudd-O

Rudd-O — Wed, 18 Jan 2006 19:02:07 +0000

It seems the layout problems are timing-related, basically when this server is feeding the HTML to your browser at a slow rate, and at certain, key, points, a burst of HTML comes, Firefox ends up laying out the sidebar wrongly, and then you see it "on top" of the content, or some other weirdness.

The validator at the W3C site does not seem to complain about this page, though.

Out of my control =(.

By: KBeaumont

KBeaumont — Wed, 18 Jan 2006 18:52:03 +0000

Jim: It also looks good here on both FC4 Firefox 1.5 desktop & OpenSuse 10 Firefox 1.5.

By: Rudd-O

Rudd-O — Wed, 18 Jan 2006 17:10:41 +0000

Jim: it looks perfectly on my Firefox 1.0.7 in my FC4 deployment… what did look wrong?

By: Anonymous Bosch

Anonymous Bosch — Wed, 18 Jan 2006 06:01:22 +0000

"I start my Linux box with no space set aside for swap but let it allocate swap on an as-needed basis in 64MB chunks."

Can you explain how to configure this?

Many thanks.

By: Jim

Jim — Wed, 18 Jan 2006 06:00:12 +0000

I see that you used Wordpress to generate the page. Kinda ironic but using Firefox 1.5 to view the page renders it almost unreadable while using IE it renders perfect. This is a blog about Linux too!!!

By: MikeFM

MikeFM — Wed, 18 Jan 2006 04:54:28 +0000

The best idea IMO is to let the system adjust swap space as needed. I start my Linux box with no space set aside for swap but let it allocate swap on an as-needed basis in 64MB chunks. Works well by not slowing the system with swap you don’t really need or allowing the system to really grind to a halt by running out of memory.