remap_file_pages - create a nonlinear file mapping
#define _GNU_SOURCE /* See feature_test_macros(7) */
int remap_file_pages(void *addr, size_t size, int prot,
size_t pgoff, int flags);
: this system call was marked as deprecated starting with Linux 3.16.
In Linux 4.0, the implementation was replaced by a slower in-kernel 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.
() 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
() 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:
- Use mmap(2) to create a mapping (which is initially
linear). This mapping must be created with the MAP_SHARED
- 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.
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.
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
specifies the address at which the file pages identified by
will be placed.
The values specified in addr
should be multiples of the
system page size. If they are not, then the kernel rounds both
to the nearest multiple of the page size.
argument must be specified as 0.
argument has the same meaning as for mmap
(2), but all
flags other than MAP_NONBLOCK
On success, remap_file_pages
() returns 0. On error, -1 is returned, and
is set appropriately.
- addr does not refer to a valid mapping created with
the MAP_SHARED flag.
- addr, size, prot, or pgoff is
() system call appeared in Linux 2.5.46; glibc
support was added in version 2.3.3.
() system call is Linux-specific.
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.
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