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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 because the kernel code for this system call was com‐
       plex,  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 ad‐
       ditional 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 re‐
       gion 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 mul‐
       tiple 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 to indicate the error.

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)

Linux                                                                          2021-03-22                                                            REMAP_FILE_PAGES(2)