Subject: Re: mfs woes
To: None <>
From: David Young <>
List: tech-kern
Date: 07/13/2004 22:39:48
On Tue, Jul 13, 2004 at 11:17:20PM -0400, Steven M. Bellovin wrote:
> In message <>, Andrew Brown writes:
> >On Tue, Jul 13, 2004 at 05:18:31PM -0500, David Young wrote:
> >>I am told that blocks in the memory filesystem (mfs) can end up in the
> >>buffer cache: this double-whammy on memory can lead to memory exhaustion.
> >
> >yes, 'cause it's a "file system".
> >
> >>The problem is compounded (I do not understand how or why) when multiple
> >>mfs are in use.
> >>
> >>Is there any bug-fix or work-around for the memory-inefficiency/exhaustion
> >>issue?  Can somebody outline what a fix would look like?
> >
> >write a real swap-based file system?  mfs also comes with a ~2.9
> >gigabyte limit (on i386, at least).  when using USE_TOPDOWN_VM.  when
> >you're not, it comes with a ~1.8 gigabyte limit.  regardless of how
> >much ram or swap you have.
> Given the new buffer cache architecture, I've been wondering if mfs 
> even makes sense these days.  Perhaps a disk partition mounted with 
> async would provide comparable performance?  I don't know; I haven't 
> tried it.  But I'm getting ready to bring up a new machine; I might 
> reserve a partition and see what happens.

I think that an in-memory filesystem makes the most sense for my
applicatoin: I am using either a CompactFlash card or a CD-ROM as the
"hard drive."  I do not want to keep volatile information on the former;
I cannot keep it on the latter.


David Young             OJC Technologies      Urbana, IL * (217) 278-3933