lkml.org 
[lkml]   [1998]   [Dec]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: mmap() is slower than read() on SCSI/IDE on 2.0 and 2.1
On Sat, Dec 19, 1998 at 04:37:34PM +0100, Rogier Wolff wrote:
> Marc Lehmann wrote:
> > On Thu, Dec 17, 1998 at 06:52:50AM +0000, Linus Torvalds wrote:
> > > Umm, the easiest hint is probably to just look at the faulting address.
> > > We have it available, after all.
> > >
> > > I suspect that such a simple heuristic would be fairly accurate, and it
> > > can be coupled with other heuristics to further increase the accuracy.
> >
> > file copy, yes. But grep (and probably lots of others) don't access memory
> > sequentially (as faster search algorithms exist)
>
> A fast search algorithm, touches memory every n bytes where n is the
> size of the largest constant string that you're searching for.

A a small threshold might catch fgrep, but it will also increase the
possibility for false "hits".

Other (important) types of searches (for example a linear search in a
database table) might not offer such behaviour.

In any case, that makes an excellent heuristic if combined with watching page
access ordering.

And it might well give a good heuristic when used alone (but I'd benchmark it
;)

--
Happy New Year, I'll be away from 21. Dec to 7. Jan

-----==- |
----==-- _ |
---==---(_)__ __ ____ __ Marc Lehmann +--
--==---/ / _ \/ // /\ \/ / pcg@goof.com |e|
-=====/_/_//_/\_,_/ /_/\_\ --+
The choice of a GNU generation |
|

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

\
 
 \ /
  Last update: 2005-03-22 13:46    [W:0.902 / U:0.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site