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

NAME
       alloc_hugepages, free_hugepages - allocate or free huge pages

SYNOPSIS
       void *syscall(SYS_alloc_hugepages, int key, void *addr, size_t len,
                     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
       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
       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
       ENOSYS The system call is not supported on this kernel.

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

NOTES
       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.

Linux                                                                          2021-03-22                                                             ALLOC_HUGEPAGES(2)