remap_file_pages(2) — Linux manual page


remap_file_pages(2)        System Calls Manual       remap_file_pages(2)

NAME         top

       remap_file_pages - create a nonlinear file mapping

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #define _GNU_SOURCE         /* See feature_test_macros(7) */
       #include <sys/mman.h>

       [[deprecated]] int remap_file_pages(void addr[.size], size_t size,
                                           int prot, size_t pgoff, int flags);

DESCRIPTION         top

       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         top

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

ERRORS         top

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

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

STANDARDS         top


HISTORY         top

       Linux 2.5.46, glibc 2.3.3.

NOTES         top

       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         top

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

Linux man-pages (unreleased)     (date)              remap_file_pages(2)

Pages that refer to this page: mincore(2)mmap(2)syscalls(2)