REMAP_FILE_PAGES(2)       (2017-09-15)        REMAP_FILE_PAGES(2)

     NAME
          remap_file_pages - create a nonlinear file mapping

     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);

     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 appli-
          cations 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 sys-
          tems, those use cases don't exist on 64-bit systems.

          The remap_file_pages() system call is used to create a non-
          linear 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 lin-
             ear).  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

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     REMAP_FILE_PAGES(2)       (2017-09-15)        REMAP_FILE_PAGES(2)

          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 appropriately.

     ERRORS
          EINVAL
               addr does not refer to a valid mapping created with the
               MAP_SHARED flag.

          EINVAL
               addr, size, prot, or pgoff is invalid.

     VERSIONS
          The remap_file_pages() system call appeared in Linux 2.5.46;
          glibc support was added in version 2.3.3.

     CONFORMING TO
          The remap_file_pages() system call is Linux-specific.

     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)

     COLOPHON
          This page is part of release 5.10 of the Linux man-pages
          project.  A description of the project, information about
          reporting bugs, and the latest version of this page, can be
          found at https://www.kernel.org/doc/man-pages/.

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