Re: fadvise syscall?

[Anton Altaparmakov]

At 19:20 17/03/02, Joel Becker wrote:
>On Sun, Mar 17, 2002 at 01:41:37PM +0000, Anton Altaparmakov wrote:
> > When you want large data streaming, i.e. you start getting worried about
> > memory pressure, then you want open(2) + O_DIRECT. No caching done. 
> Perfect
> > for large data streams and we have that already. I agree that you may want
> > some form of asynchronous read ahead with passed pages being dropped from
> > the cache but that could be just a open(2) + O_SEQUENTIAL (doesn't 
> exist yet).
>
>         O_DIRECT isn't the right thing for large streaming.  You want
>readahead and dropbehind.  O_DIRECT takes substantial penalties for its
>lack of copy/cacheing.  This works fine in certain circumstances
>(applications that keep their own caching), but for something like a
>video or mp3, you'll win with working dropbehind easily.

Oh absolutely. For mp3s, dvds, etc. Note I wrote O_SEQUENTIAL... Perhaps I 
didn't emphasize it enough. In multimedia applications you very well know 
in advance what you want so you can specify it at open(2) time.

Best regards,

Anton