alloc_hugepages(2) — Linux manual page

NAME \| SYNOPSIS \| DESCRIPTION \| RETURN VALUE \| ERRORS \| FILES \| STANDARDS \| HISTORY \| NOTES \| COLOPHON

alloc_hugepages(2)         System Calls Manual         alloc_hugepages(2)

NAME top

       alloc_hugepages, free_hugepages - allocate or free huge pages

SYNOPSIS top

       void *syscall(size_t size;
                     SYS_alloc_hugepages, int key, void addr[size], size_t size,
                     int prot, int flag);
       int syscall(SYS_free_hugepages, void *addr);

       Note: glibc provides no wrappers for these system calls,
       necessitating the use of syscall(2).

DESCRIPTION top

       The system calls alloc_hugepages() and free_hugepages() were
       introduced in Linux 2.5.36 and removed again in Linux 2.5.54.
       They existed only on i386 and ia64 (when built with
       CONFIG_HUGETLB_PAGE).  In Linux 2.4.20, the syscall numbers exist,
       but the calls fail with the error ENOSYS.

       On i386 the memory management hardware knows about ordinary pages
       (4 KiB) and huge pages (2 or 4 MiB).  Similarly ia64 knows about
       huge pages of several sizes.  These system calls serve to map huge
       pages into the process's memory or to free them again.  Huge pages
       are locked into memory, and are not swapped.

       The key argument is an identifier.  When zero the pages are
       private, and not inherited by children.  When positive the pages
       are shared with other applications using the same key, and
       inherited by child processes.

       The addr argument of free_hugepages() tells which page is being
       freed: it was the return value of a call to alloc_hugepages().
       (The memory is first actually freed when all users have released
       it.)  The addr argument of alloc_hugepages() is a hint, that the
       kernel may or may not follow.  Addresses must be properly aligned.

       The size argument is the size of the required segment.  It must be
       a multiple of the huge page size.

       The prot argument specifies the memory protection of the segment.
       It is one of PROT_READ, PROT_WRITE, PROT_EXEC.

       The flag argument is ignored, unless key is positive.  In that
       case, if flag is IPC_CREAT, then a new huge page segment is
       created when none with the given key existed.  If this flag is not
       set, then ENOENT is returned when no segment with the given key
       exists.

RETURN VALUE top

       On success, alloc_hugepages() returns the allocated virtual
       address, and free_hugepages() returns zero.  On error, -1 is
       returned, and errno is set to indicate the error.

ERRORS top

       ENOSYS The system call is not supported on this kernel.

FILES top

       /proc/sys/vm/nr_hugepages
              Number of configured hugetlb pages.  This can be read and
              written.

       /proc/meminfo
              Gives info on the number of configured hugetlb pages and on
              their size in the three variables HugePages_Total,
              HugePages_Free, Hugepagesize.

STANDARDS top

       Linux on Intel processors.

HISTORY top

       These system calls are gone; they existed only in Linux 2.5.36
       through to Linux 2.5.54.

NOTES top

       Now the hugetlbfs filesystem can be used instead.  Memory backed
       by huge pages (if the CPU supports them) is obtained by using
       mmap(2) to map files in this virtual filesystem.

       The maximal number of huge pages can be specified using the
       hugepages= boot parameter.

COLOPHON top

       This page is part of the man-pages (Linux kernel and C library
       user-space interface documentation) project.  Information about
       the project can be found at 
       ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
       for this manual page, see
       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
       This page was obtained from the tarball man-pages-6.15.tar.gz
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       man-pages@man7.org

Linux man-pages 6.15            2025-06-28             alloc_hugepages(2)

Pages that refer to this page: syscalls(2), unimplemented(2)