The global algorithm for memory allocation is the following:
A request is received for a block of N bytes.
- Try to allocate it with malloc() and return the block
if successful.
- If malloc() failed, try to create a VM file on disk,
map it using mmap() and return the resulting pointer.
- If no VM file can be created, fail (exit).
The third kind of memory allocation (large file mapping) should be handled by the following algorithm:
A request is received for a mapping of a file,
N bytes starting from offset START in the file.
- If the file is already mapped, return the appropriate
pointer (file pointer + START bytes).
- Map the file, return the appropriate pointer or NULL
if the file cannot be mapped.
Deallocating such a pointer means decreasing a counter on the file mapping. If the counter reaches zero, the file can be unmapped.