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 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.

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 4.15 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/.

Linux                                              2017-09-15                                REMAP_FILE_PAGES(2)