alloc_hugepages(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | FILES | CONFORMING TO | NOTES | COLOPHON

ALLOC_HUGEPAGES(2)      Linux Programmer's Manual     ALLOC_HUGEPAGES(2)

NAME         top

       alloc_hugepages, free_hugepages - allocate or free huge pages

SYNOPSIS         top

       void *alloc_hugepages(int key, void *addr, size_t len,
                             int prot, int flag);
       int free_hugepages(void *addr);

DESCRIPTION         top

       The system calls alloc_hugepages() and free_hugepages() were
       introduced in Linux 2.5.36 and removed again in 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 len argument is the length 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.

CONFORMING TO         top

       These extinct system calls were specific to Linux on Intel
       processors.

NOTES         top

       These system calls are gone; they existed only in Linux 2.5.36
       through to 2.5.54.  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 release 5.11 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                          2021-03-22             ALLOC_HUGEPAGES(2)

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