[PVFS2-users] mmap() support?

Rob Ross rross at mcs.anl.gov
Fri Oct 21 17:53:46 EDT 2005


Hi Martin,

We definitely do *not* support shared mmap().  I would expect that we 
will never ever support that -- it very much goes against the PVFS2 
model.  Sorry!

Regarding the delays, I don't recall any previous reports of this sort 
of behavior.  I agree that it is confusing.  "less" is a read 
application too, right?  So there must be something different about 
*how* vi and less are accessing the file.

Perhaps we should strace them and see what they're doing that is different?

Thanks for keeping us on our toes!

Rob

mcuma wrote:
> Hello,
> 
> We just upgraded to ver. 1.3.0, and, the problems we have had earlier 
> are gone. Thanks as always for your hard work developing the package.
> 
> However, we are seeing some new issues....
> 
> First of all, one of our users reports problems when trying to use 
> mmap() to operate on a file. I am wondering if this is something PVFS2 
> does not support. In any case, attached is a program that is 
> demonstrating the problem.
> To run, do:
> a.out <from_file_name> <to_file_name>
> the error we're seeing is reported as:
> mmap error for input
> mmap error for output
> Segmentation fault
> 
> There are also two other issues.
> 
> One was already reported - it's the messed up time stamps upon file 
> creation.
> 
> The other is somewhat more subtle - we are seeing considerable delays 
> (~5 minutes) when accessing the files on PVFS2, even small ones, with 
> commands like vi, less,... Interestingly, using cat, more,... is pretty 
> fast, which makes me to believe that the slowdown happens when the file 
> is opened for writing. However, I haven't seen any delays on MPI-IO or 
> UNIX I/O issued from a program, so, it's confusing. Does anyone else see 
> this kind of delay?
> 
> We're running (I believe) 12 I/O servers on x86-64 (SuSE 9.0, I believe 
> - Brian, correct me if I am wrong). The clients are all x86-64 running 
> SuSE 9.0 with 2.6.11 kernel.


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