Subject: Re: Is O_DIRECT useless on NetBSD?
To: Roland Illig <>
From: Antti Kantee <>
List: tech-kern
Date: 11/21/2007 17:17:48
On Wed Nov 21 2007 at 16:08:59 +0100, Roland Illig wrote:
> Antti Kantee wrote:
> >On Wed Nov 21 2007 at 15:11:39 +0100, Roland Illig wrote:
> >
> >>>Since I expect the program to not read any data twice, I added the 
> >
> >What about other programs? ;)
> Cannot be. :) First, I freed some memory by using "yes | less", and when 
> I interrupted that, I had 300 MB free. Then I started my archiver, and 
> the free memory decreased with approximately the speed of data consumed 
> by it.

No I meant how do you know other programs won't be accessing the data
you are processing with your archiver.

> So am I right that currently there is no way for a program to say "I 
> will write some data to that file, and nobody is going to use it in the 
> next time, so please don't buffer it"?
> I'm asking because it is pretty annoying that the cached data for 
> programs I often run (like firefox, eclipse) is displaced by data that 
> will not be used. That makes starting these programs very slow.

I'm not sure.  You could try mmap + madvise, e.g. madvise MADV_FREE
after processing if you're *sure* you won't never ever access the data in
another program.  But that's slightly tedious in any case as you need to
truncate + move window + do io.  Ok, might not be that much more tedious.

Antti Kantee <>                     Of course he runs NetBSD                
    "la qualité la plus indispensable du cuisinier est l'exactitude"