[WBEL-users] OT: Fwd: Re: Booting linux host, getting error message (SOLVED)

[A Streetcar Named]

On Fri, 13 Aug 2004 09:46:23 -0600, James Knowles
<jamesk@ifm-services.com> wrote:
> >the semantics of a file system are such that the data
> >remains in place even if it's not utilised,
> No, there are no such semantics in a file system (leaving room for
> special-purpose file systems). What you describe is not by design but a
> side-effect of the fact that magnetic disk storage technology is
> persistent. Leaving that old data around is bad from a security
> standpoint, but good from a performance standpoint.
> 
> If the medium is not persistent, then there is no reason why the old
> data must persist.

I still think this is part of the filesystem.  The fact that tmpfs
fuzzes over medium and filesystem makes it confusing, but if we
created ext2/3, reiserfs, etc. on a tmpfs medium, they still leave
data around persistently.  A hypothetical paranoid file system could
choose to scrub all data that has been removed...  But anyway, medium
vs. filesystem is really not an issue =)

> >/dev/anon functionality
> I'm not familar with this, except from the article. It appears to be
> solving a different problem space revolving around the kernel's
> interaction with filesystems, and not tmpfs itself. The Linux kernel is
> pretty aggressive about caching because disks are very slow compared to
> RAM and CPU. With UML, the kernel is unaware that it's not sitting on an
> atypical situation.
> 
> I could be wrong there, of course. That's what I gleaned from a quick scan.

I think you're right!  I now think that tmpfs does return space
occupied by deleted files to the VM, and that /dev/anon's additional
functionality is that existing files which are mmap'ed will also
return space to the VM when portions of the file are un-map'ed...