Re: free (command) memory question

From: David Wright (david_c_wright_at_hotmail.com)
Date: 07/12/04 

Date: Mon, 12 Jul 2004 10:15:20 +0200

Paranoid about Spam wrote:

> I asked about a memory leak a few days ago, and was relieved to find the
> free command.
>
> I just ran the free command and it shows as follows:
> total used free shared buffers cached
> Mem: 516520 472164 44356 0 108500 218848
> -/+ buffers/cache: 144816 371704
> Swap: 1044216 0 1044216
>
>
> Does this mean that I actually have 371mb of free memory that's being
> used for cache and buffers? and 144mb that's actually being used by
> applications?

Not certain, I haven't analysed free before and man page doesn't explain the
output (VERY USEFUL!); but I did a quick analysis of the column headings
and the figures involved and:

NOTE: Display is in KB, /1024 for MB.

I would say that the first line means 461MB is used for the OS and App
caches etc. with 43.3MB free. Of the used memory 105MB is buffers and 213MB
is cached.

This should mean that (according to the second line) you have 141MB used by
applications, and it can call on another 363MB of physical memory for
programs.

And you have 1019MB of disk space allocated for Swap.

I would suggest, that the 363MB free for data/apps won't be 100% correct, I
would assume Linux always keeps a little physical memory for buffers and
cache, so I would expect it to start swapping before all of the additional
363MB are used, but I don't know what % (or preset amount) it would use as
a minimum for buffers and cache. I haven't delved that deeply into the
internal workings of the Kernel...

Hope that helps clear it up a bit. I think I have the figures right, at
least doing the calculations the way I have, the figures all add up... But
there again, I could be heading off at a tangent here ;-)

Dave

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