создать нелинейное отображение файлов (create a nonlinear file mapping)
Имя (Name)
remap_file_pages - create a nonlinear file mapping
Синопсис (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);
Описание (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-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.
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.
Возвращаемое значение (Return value)
On success, remap_file_pages() returns 0. On error, -1 is
returned, and errno is set to indicate the error.
Ошибки (Error)
EINVAL addr does not refer to a valid mapping created with the
MAP_SHARED flag.
EINVAL addr, size, prot, or pgoff is invalid.
Версии (Versions)
The remap_file_pages() system call appeared in Linux 2.5.46;
glibc support was added in version 2.3.3.
Стандарты (Conforming to)
The remap_file_pages() system call is Linux-specific.
Примечание (Note)
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.
Смотри также (See also)
getpagesize(2), mmap(2), mmap2(2), mprotect(2), mremap(2),
msync(2)
