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.
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 programs 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.
/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,