lkml.org 
[lkml]   [2002]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: fadvise syscall?
Jeff Garzik wrote:
>
> Has anyone ever done an madvise(2)-type syscall for file descriptors?
> (or does the capability exist and I'm missing it?)

Well, question is: is madvise() any use? :)

> I was thinking, in playing around with stuff like cp(1) I've found that
> standard read(2) and write(2) of a 4-8K buffer is the fastest solution
> overall, in addition to providing the useful side effect of better error
> reporting, such as ENOSPC report. Better error reporting than the
> alternative I see anyway, mmap(2).

4k to 8k is best on x86 at least. And if you're actually going to *use*
each byte in the file, the zero-copy characteristics of mmap aren't
worth much at all.

> So... we have madvise, why not fadvise? I would love the capability for
> applications to provide hints to the OS like madvise, but for file
> descriptors...

The one hint which I can think of which would be beneficial would
be an equivalent to MADV_SEQUENTIAL. Something which says "this
is a big streaming read/write - don't go and evict other stuff because
of it". O_STREAMING perhaps. Or working dropbehind heuristics,
although I suspect that explicit controls will always do better.

For MADV_RANDOM, readahead window scaling should get that right.

What else were you thinking of?

-
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:25    [from the cache]
©2003-2011 Jasper Spaans