Section (2) remap_file_pages
remap_file_pages — create a nonlinear file mapping
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sys/mman.h>
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_zsingle_quotesz_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
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:
Use mmap(2) to create a mapping (which is initially linear). This mapping must be created with the
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.
specify the region of the file that is to be relocated within
a file offset in units of the system page size;
size is the length of the
region in bytes.
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
addr specifies the address at
which the file pages identified by
size will be placed.
The values specified in
size should be multiples of the
system page size. If they are not, then the kernel rounds
down to the nearest
multiple of the page size.
must be specified as 0.
has the same meaning as for mmap(2), but all flags
remap_file_pages() returns 0. On error,
−1 is returned, and
is set appropriately.
addrdoes not refer to a valid mapping created with the
system call appeared in Linux 2.5.46; glibc support was added
in version 2.3.3.
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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Copyright (C) 2003, Michael Kerrisk <mtk.manpagesgmail.com>
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2003-12-10 Initial creation, Michael Kerrisk <mtk.manpagesgmail.com>
2004-10-28 aeb, corrected prototype, prot must be 0