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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 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

       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


       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
       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.


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


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