REMAP_FILE

NAME

remap_file_pages - create a non-linear file mapping

SYNOPSIS

#include <sys/mman.h>

void *remap_file_pages(void *start, size_t size, int prot, ssize_t pgoff, int flags);

DESCRIPTION

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:

1.: Use mmap() to create a mapping (which is initially linear). This mapping must be created with the MAP_SHARED flag.
2.: 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 is ignored, and must be specified as 0. In the future, it may be possible to use this argument to change the protection of the pages of the specified region without creating a new VMA (as is done by mprotect()).

The flags argument has the same meaning as for mmap(), but all flags other than MAP_NONBLOCK are ignored.

RETURN VALUE

On success, remap_file_pages() returns 0. On error, -1 is returned, and errno is set appropriately.

NOTES

The remap_file_pages() system call appeared in Linux 2.5.46.

ERRORS

EINVAL: start does not refer to a valid mapping created with the MAP_SHARED flag.
EINVAL: start, size, or pgoff is invalid.

CONFORMING TO

The remap_file_pages() system call is Linux specific.

REMAP_FILE_PAGES