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       remap_file_pages - create a nonlinear file mapping


       #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);


       Note:  this  system  call  is  (since  Linux  3.16) deprecated and will
       eventually be replaced by a  slower  in-kernel  emulation.   Those  few
       applications  that  use  this  system call should consider migrating to

       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.


       On success, remap_file_pages() returns 0.  On error,  -1  is  returned,
       and errno is set appropriately.


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

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


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


       The remap_file_pages() system call is Linux-specific.


       Since Linux 2.6.23, remap_file_pages() creates non-linear mappings only
       on in-memory file systems  such  as  tmpfs,  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.


       getpagesize(2), mmap(2), mmap2(2), mprotect(2), mremap(2), msync(2)


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