remap_file_pages

REMAP_FILE_PAGES(2)        Linux Programmer's Manual       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  applications that use this system call
       should consider migrating to alternatives.  This change  was  made  be-
       cause  the  kernel code for this system call was complex, and it is be-
       lieved 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  map-
       ping, 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  corre-
          spondence  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 map-
       ping 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 sup-
       port 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 5.05 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)