Considerations for the mmap usage

These considerations are for the applications that use mmap.

For applications, which are using memory mapped I/O (mmap) to access data on GPFS, memory mappings are separate from the GPFS pagepool and any changes made by using the mmap I/O are not immediately visible after a regular read system call. This is allowed by the POSIX standard, but is different behavior from other Linux and AIX file systems.
For applications, which access the same data by using the mmap I/O and non-mmap I/O, explicitly call msync() or munmap() when data is written by using the mmap. Because this data must be visible to access by using the non-mmap I/O.