Re: Is Greenspun enough?

Ulrich Hobelmann <u.hobelmann@xxxxxx> wrote:

> No, I'm just talking about the way memory is handled on most current
> systems. If I had time to do my own system, it'd include a file-open
> flag called don't-cache-this-file, so the file would be cached with
> lowest priority (dropped from cache as soon as anything else needed
> memory). I'm not sure most current system even have memory priorities
> (like they do have scheduling priorities), only some basic LRU.
>

from man 2 open on Linux:

O_DIRECT
Try to minimize cache effects of the I/O to and from this file.
In general this will degrade performance, but it is useful in
special situations, such as when applications do their own
caching. File I/O is done directly to/from user space buffers.
The I/O is synchronous, i.e., at the completion of the read(2)
or write(2) system call, data is guaranteed to have been trans-
ferred. Under Linux 2.4 transfer sizes, and the alignment of
user buffer and file offset must all be multiples of the logical
block size of the file system. Under Linux 2.6 alignment to
512-byte boundaries suffices.
A semantically similar interface for block devices is described
in raw(8).


Not exactly what you want, but with a little extra userspace code you
get equivalent effect.

--
Waldek Hebisch
hebisch@xxxxxxxxxxxxxxxx
.

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