Memory-Mapped Files (see Fig. 6.7)

Figure 6.7: Left: (a) Segmented process before mapping files into its address space (b) Process after mapping existing file abc into one segment creating new segment for xyz. Right: Memory mapped files and paging

• Avoids translating from on-disk format to in-memory format (and vice versa)
  • Supports complex structures
  • No read/write systems calls
  • File simply (paged or swapped) to file system
  • Unmap when finished
• Problems
  • Determining actual file size after modification; Round to nearest whole page (even if only 1 byte file)
  • Care must be taken if file is shared; E.g. one process memorymapped and one process read/write syscalls
  • Large files may not fit in the virtual address space