remap_file_pages - create a non-linear file mapping
SYNOPSIS
#define _GNU_SOURCE#include <sys/mman.h>int remap_file_pages(void *addr, 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(2)
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
addr
argument serves two purposes.
First, it identifies the mapping whose pages we want to rearrange.
Thus,
addr
must be an address that falls within
a region previously mapped by a call to
mmap(2).
Second,
addr
specifies the address at which the file pages
identified by
pgoff
and
size
will be placed.
The values specified in
addr
and
size
should be multiples of the system page size.
If they are not, then the kernel rounds
both
values
down
to the nearest multiple of the page size.
The
prot
argument must be specified as 0.
The
flags
argument has the same meaning as for
mmap(2),
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.
ERRORS
EINVAL
addr
does not refer to a valid mapping
created with the
MAP_SHARED
flag.
EINVAL
addr,
size,
prot,
or
pgoff
is invalid.
VERSIONS
The
remap_file_pages()
system call appeared in Linux 2.5.46;
glibc support was added in version 2.3.3.
CONFORMING TO
The
remap_file_pages()
system call is Linux-specific.
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
