free_hugepages

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



NAME
       alloc_hugepages, free_hugepages - allocate or free huge pages

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

       int free_hugepages(void *addr);

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 return 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’ memory or to free them again.	Huge pages are locked
       into memory, and are not swapped.

       The  key	 parameter 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 parameter 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
       parameter  of  alloc_hugepages() is a hint, that the kernel may or may
       not follow.  Addresses must be properly aligned.

       The len parameter is the length of the required segment. It must be  a
       multiple of the huge page size.

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

       The flag parameter 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 appropriately.

ERRORS
       ENOSYS The system call is not supported on this kernel.

CONFORMING TO
       These  calls  existed  only in Linux 2.5.36 - 2.5.54.  These calls are
       specific to Linux on Intel processors, and should not be used in	 pro-
       grams  intended	to  be	portable. Indeed, the system call numbers are
       marked for reuse, so programs using these may do something random on a
       future 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.

NOTES
       The system calls are gone. Now the hugetlbfs filesystem	can  be	 used
       instead.	  Memory  backed  by huge pages (if the CPU supports them) is
       obtained by mmap’ing files in this virtual filesystem.

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





Linux 2.5.36			  2003-02-02		   ALLOC_HUGEPAGES(2)