remap_file_pages(2) - Linux manual page (original) (raw)

remapfilepages(2) System Calls Manual remapfilepages(2)

NAME top

   remap_file_pages - create a nonlinear file mapping

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#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 top

   **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)](../man2/mmap.2.html) 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)](../man2/mmap.2.html) 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)](../man2/mmap.2.html).  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)](../man2/mmap.2.html), but all
   flags other than **MAP_NONBLOCK** are ignored.

RETURN VALUE top

   On success, **remap_file_pages**() returns 0.  On error, -1 is
   returned, and _[errno](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   **EINVAL** _addr_ does not refer to a valid mapping created with the
          **MAP_SHARED** flag.

   **EINVAL** _addr_, _size_, _prot_, or _pgoff_ is invalid.

STANDARDS top

   Linux.

HISTORY top

   Linux 2.5.46, glibc 2.3.3.

NOTES top

   Since Linux 2.6.23, **remap_file_pages**() creates non-linear mappings
   only on in-memory filesystems such as [tmpfs(5)](../man5/tmpfs.5.html), hugetlbfs or
   ramfs.  On filesystems with a backing store, **remap_file_pages**() is
   not much more efficient than using [mmap(2)](../man2/mmap.2.html) to adjust which parts
   of the file are mapped to which addresses.

SEE ALSO top

   [getpagesize(2)](../man2/getpagesize.2.html), [mmap(2)](../man2/mmap.2.html), [mmap2(2)](../man2/mmap2.2.html), [mprotect(2)](../man2/mprotect.2.html), [mremap(2)](../man2/mremap.2.html),
   [msync(2)](../man2/msync.2.html)

COLOPHON top

   This page is part of the _man-pages_ (Linux kernel and C library
   user-space interface documentation) project.  Information about
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   part of the original manual page), send a mail to
   man-pages@man7.org

Linux man-pages 6.10 2024-07-23 remapfilepages(2)

Pages that refer to this page:mincore(2), mmap(2), syscalls(2)