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
       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 5.03 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)