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SubjectRe: raw drive access for databases
On Wed, Nov 04, 1998 at 12:51:03PM -0500, Gregory Maxwell wrote:
> On Wed, 4 Nov 1998, Meelis Roos wrote:
> > Or an option for open() like O_NOCACHE. In fact, fcntl() seems to be more
> > flexible since you can turn it on and off whenever you want (but who needs
> > that?).
> >
> > Multimedia applications would also benefit from this.
>
> Yes.. Multimedia would REALLY benifit. It would be nice to play a big mpg
> or avi without it throwing everything else out of my buffercache..

Another way to handle streaming is to inform the kernel that it may as
well discard pages after they've been used by the mpg player, if no-one
else is using them. I prefer this because it permits the kernel to use
the pages if they are in cache for some reason, it lets the kernel
decide on readahead policies according to device speed etc. (in
principle), and the kernel can keep the data around anyway if it wants,
for another process or simply because there's loads of free memory.

madvice(MADV_SEQUENTIAL) is one mechanism for this, which Linux doesn't
have. It gets mentioned from time to time.

Discardable pages is another that was discussed in a thread a while
back. I have most of the implementation of this one done, now if I can
only find the motivation to finish the darn thing...

-- Jamie

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