NAME¶
remap_file_pages - create a nonlinear file mapping
SYNOPSIS¶
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <sys/mman.h>
int remap_file_pages(void *addr, size_t size, int prot,
size_t pgoff, int flags);
DESCRIPTION¶
Note: this system call is (since Linux 3.16) deprecated and will
eventually be replaced by a slower in-kernel emulation. Those few applications
that use this system call should consider migrating to alternatives.
The
remap_file_pages() system call is used to create a nonlinear mapping,
that is, a mapping in which the pages of the file are mapped into a
nonsequential 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 nonlinear 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.
The
remap_file_pages() system call is Linux-specific.
NOTES¶
Since Linux 2.6.23,
remap_file_pages() creates non-linear mappings only
on in-memory file systems such as tmpfs, hugetlbfs or ramfs. On filesystems
with a backing store,
remap_file_pages() is not much more efficient
than using
mmap(2) to adjust which parts of the file are mapped to
which addresses.
SEE ALSO¶
getpagesize(2),
mmap(2),
mmap2(2),
mprotect(2),
mremap(2),
msync(2)
COLOPHON¶
This page is part of release 3.74 of the Linux
man-pages project. A
description of the project, information about reporting bugs, and the latest
version of this page, can be found at
http://www.kernel.org/doc/man-pages/.
