[OpenAFS] mmap and AFS?

Mon, 06 Dec 2010 09:39:34 -0500

This is a multi-part message in MIME format.
--------------080309000203000906050400
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

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 
solution for user home directories.  After working on this awhile, he 
thinks there may be a show-stopper.  Is there an problem with using AFS 
with applications 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 "man mmap" on any unix or macos machine). Memory mapping is
    used to reduce seek 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.  I'm also not sure which 
type/version/kernel of Linux he's running on the server end.

Thank you for any help/suggestions.

Chris

--------------080309000203000906050400
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>

    <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
  </head>
  <body bgcolor="#ffffff" text="#000000">
    AFS gurus,<br>
    <br>
    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 solution for user home directories.&nbsp; After working on
    this awhile, he thinks there may be a show-stopper.&nbsp; Is there an
    problem with using AFS with applications that use mmap to solve
    IO-bound issues?<br>
    <blockquote><br>
      The problem is a esoteric issue called memory mapping. We have<br>
      applications that we use extensively in geophysics that use memory<br>
      mapping to improve performance. The relevant C function is "mmap"
      (run "man mmap" on any unix or macos machine). Memory mapping is
      used to reduce seek times when a program does a lot random access
      IO, and is a well known performance trick for IO-bound
      applications.<br>
      <br>
      Now I haven't written a simple test program to isolate the problem
      to<br>
      this specific issue, BUT I know that applications I use daily and
      that I<br>
      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<br>
      served by nfs. Thus the memory mapping hypothesis is a strong
      possibility.<br>
      <br>
      Is this a know limitation? If so, is there a solution?<br>
      <br>
    </blockquote>
    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.&nbsp; I'm also not sure which
    type/version/kernel of Linux he's running on the server end.<br>
    <br>
    Thank you for any help/suggestions. <br>
    <br>
    Chris<br>
  </body>
</html>

--------------080309000203000906050400--