alloc_hugepages, free_hugepages - allocate or free huge pages
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 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.
On success,
alloc_hugepages() returns the allocated virtual address, and
free_hugepages() returns zero. On error, -1 is returned, and
errno is set appropriately.
- ENOSYS
- The system call is not supported on this 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, Hugepagesize.
These calls are specific to Linux on Intel processors, and should not be used in
programs intended to be portable.
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.