RAM usage

[synrg at sanctuary.nslug.ns.ca (Ben Armstrong)]

On Sat, 15 Sep 2007 11:18:09 +1200
"Angus McMorland" <amcmorl at gmail.com> wrote:
> I've made a debian live CD to allow me to perform some modelling. The
> machines I have available to play with have 2 GB of RAM, which is
> normally a lot more than enough to run my work. However, debian live's
> tmpfs (I presume) seems to be taking up about >1 GB of that RAM,

I'm not sure if that assumption is correct.

http://lxr.linux.no/source/Documentation/filesystems/tmpfs.txt

tmpfs puts everything into the kernel internal caches and grows and
shrinks to accommodate the files it contains and is able to swap
unneeded pages out to swap space. It has maximum size limits which
can be adjusted on the fly via 'mount -o remount ...'


Doesn't this mean that what df reports as 'used' is all that is actually
in tmpfs, and the "free" is just an upper limit (which is deceptive with
multiple tmpfs mounts ... it's just showing the difference between used
and the upper limit, not actual free space).

But that leaves a mystery ... why is the top 1G not visible to 'free'?