Greg Lindahl wrote:
On Thu, Sep 25, 2008 at 10:19:26AM -0400, Joe Landman wrote:
BLAST uses mmap'ed IO. This has some interesting ... interactions ...
with parallel file systems.
The PathScale compilers use mmap on their temporary files. This led to
some interesting bugs being reported... fortunately, we were able to
pinpoint the parallel filesystems as being the guilty parties without
too much work.
It looks like people use mmap files to explicitly avoid seeks,
replacing semantics of file IO with memory access semantics. We have a
customer who uses mmap for some large files (multiple GB). Sadly, mmap
on linux uses the paging mechanism which is pretty much stuck at 4kB
pages for most distributions. I think the SiCortex folks and a few
others are working with 64 kB page kernels.
I am sure there are good reasons for using mmap. I just don't know
what they are, and in what contexts. I would rather have
direct/explicit control over the IO if possible.
--
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: [EMAIL PROTECTED]
web : http://www.scalableinformatics.com
http://jackrabbit.scalableinformatics.com
phone: +1 734 786 8423 x121
fax : +1 866 888 3112
cell : +1 734 612 4615
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