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From: "Dan Maas" <dmaas@dcine.com>
To: "Stefan Hoffmeister" <lkml.2001@econos.de>
Cc: <linux-kernel@vger.kernel.org>
In-Reply-To: <fa.oqkojpv.3hosb7@ifi.uio.no> <fa.jpsks3v.1o2gag4@ifi.uio.no>
Subject: Re: VM Requirement Document - v0.0
Date: Tue, 26 Jun 2001 20:43:33 -0400
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> Windows NT/2000 has flags that can be for each CreateFile operation
> ("open" in Unix terms), for instance
>
>   FILE_ATTRIBUTE_TEMPORARY
>   FILE_FLAG_WRITE_THROUGH
>   FILE_FLAG_NO_BUFFERING
>   FILE_FLAG_RANDOM_ACCESS
>   FILE_FLAG_SEQUENTIAL_SCAN
>

There is a BSD-originated convention for this - madvise().

If you look in the Linux VM code there is a bit of explicit code for
different madvise access patterns, but I'm not sure if it's 100% supported.

Drop-behind would be really, really nice to have for my multimedia
applications. I routinely deal with very large video files (several times
larger than my RAM). When I sequentially read though such files a bit at a
time, I do NOT want the old pages sitting there in RAM while all of my other
running programs are rudely paged out...

(hrm, maybe I could hack up my own manual read-ahead/drop-behind with mmap()
and memory locking...)

Regards,
Dan