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