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Date: Sun, 17 Mar 2002 23:59:03 +0000
To: Joel Becker <jlbec@evilplan.org>
From: Anton Altaparmakov <aia21@cam.ac.uk>
Subject: Re: fadvise syscall?
Cc: Jeff Garzik <jgarzik@mandrakesoft.com>, Andrew Morton <akpm@zip.com.au>,
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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


-- 
   "I've not lost my mind. It's backed up on tape somewhere." - Unknown
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Linux NTFS Maintainer / WWW: http://linux-ntfs.sf.net/
ICQ: 8561279 / WWW: http://www-stu.christs.cam.ac.uk/~aia21/

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