The remap_file_pages() system call is used to create a non-linear
mapping, that is, a mapping in which the pages of the file are mapped into a
non-sequential order in memory. The advantage of using
remap_file_pages() over using repeated calls to mmap(2) is that
the former approach does not require the kernel to create additional VMA
(Virtual Memory Area) data structures.
To create a non-linear mapping we perform the following steps:
Use mmap() to create a mapping (which is initially
linear). This mapping must be created with the MAP_SHARED flag.
Use one or more calls to remap_file_pages() to
rearrange the correspondence between the pages of the mapping and the
pages of the file. It is possible to map the same page of a file into
multiple locations within the mapped region.
The pgoff and size arguments specify the region of the file that
is to be relocated within the mapping: pgoff is a file offset in units
of the system page size; size is the length of the region in bytes.
The start argument serves two purposes. First, it identifies the mapping
whose pages we want to rearrange. Thus, start must be an address that
falls within a region previously mapped by a call to mmap(). Second,
start specifies the address at which the file pages identified by
pgoff and size will be placed.
The prot argument must be specified as 0.
The flags argument has the same meaning as for mmap(), but all
flags other than MAP_NONBLOCK are ignored.