Subject: Re: mfs woes
To: Andrew Brown <>
From: Steven M. Bellovin <>
List: tech-kern
Date: 07/13/2004 23:17:20
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.

		--Steve Bellovin,