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SubjectRe: fadvise syscall?
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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