remap_file_pages(2) System Calls Manual remap_file_pages(2)
NAME
remap_file_pages - create a nonlinear file mapping
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <sys/mman.h>
[[deprecated]] int remap_file_pages(void addr[.size], size_t size,
int prot, size_t pgoff, int flags);
DESCRIPTION
Note: this system call was marked as deprecated starting with Linux
3.16. In Linux 4.0, the implementation was replaced by a slower in-ker-
nel emulation. Those few applications that use this system call should
consider migrating to alternatives. This change was made because the
kernel code for this system call was complex, and it is believed to be
little used or perhaps even completely unused. While it had some use
cases in database applications on 32-bit systems, those use cases don't
exist on 64-bit systems.
The remap_file_pages() system call is used to create a nonlinear map-
ping, 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 for-
mer approach does not require the kernel to create additional VMA (Vir-
tual 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 corre-
spondence 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 to indicate the error.
ERRORS
EINVAL addr does not refer to a valid mapping created with the
MAP_SHARED flag.
EINVAL addr, size, prot, or pgoff is invalid.
STANDARDS
Linux.
HISTORY
Linux 2.5.46, glibc 2.3.3.
NOTES
Since Linux 2.6.23, remap_file_pages() creates non-linear mappings only
on in-memory filesystems such as tmpfs(5), 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)
Linux man-pages 6.9.1 2024-05-02 remap_file_pages(2)
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