Joe Landman
Thu, 25 Sep 2008 11:16:23 -0700
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 _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf