Subject: Re: mfs woes
To: None <>
From: Paul Ripke <>
List: tech-kern
Date: 07/17/2004 18:04:05
On Saturday, Jul 17, 2004, at 12:40 Australia/Sydney, David Young wrote:

> 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.
>> 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?
> Discussion here and on ICB leads me to believe that md is a better bet
> than mfs, but they will both waste memory by caching.

Does anyone have plans to add something like the AIX/Linux O_DIRECT
open(2)/fcntl(2) flag and/or the AIX "dio" mount option? I think
this would have the desired effect. I'm getting a little fanatical
about the dio mount option at work - it does have a noticeable impact.

I don't know enough about our I/O path through the kernel to know how
easy this would be, but it probably should be on a long-term todo list

imho, it's somewhat more flexible than Darwin's F_NOCACHE.