[OpenAFS] mmap and AFS?

Derrick Brashear shadow@gmail.com
Mon, 6 Dec 2010 09:57:39 -0500

On Mon, Dec 6, 2010 at 9:39 AM, Chris Garrison <ecgarris@iupui.edu> wrote:
> AFS gurus,
> We have a professor who's hoping to implement our AFS cell (which as a
> service, we call RFS, the Research File System) as his department's solut=
> for user home directories.=A0 After working on this awhile, he thinks the=
> may be a show-stopper.=A0 Is there an problem with using AFS with applica=
> that use mmap to solve IO-bound issues?
> The problem is a esoteric issue called memory mapping. We have
> applications that we use extensively in geophysics that use memory
> mapping to improve performance. The relevant C function is "mmap" (run "m=
> mmap" on any unix or macos machine). Memory mapping is used to reduce see=
> times when a program does a lot random access IO, and is a well known
> performance trick for IO-bound applications.
> Now I haven't written a simple test program to isolate the problem to
> this specific issue, BUT I know that applications I use daily and that I
> know use memory mapping fail when used on data stored on rfs. The same
> application and data work fine when the files are local disk files or
> served by nfs. Thus the memory mapping hypothesis is a strong possibility=
> Is this a know limitation? If so, is there a solution?
> We are running OpenAFS 1.4.11 on the server, and I am not sure what he is
> running on the client side, but I'd imagine it's the latest stable one on
> the openafs.org site.=A0 I'm also not sure which type/version/kernel of L=
> he's running on the server end.

Asking would be better than imagining as some versions of the Linux
client had issues with mmap()

> Thank you for any help/suggestions.
> Chris