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 pro-
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 argu-
ment 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
The maximal number of huge pages can be specified using the hugepages=
This page is part of release 3.54 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2007-05-31 ALLOC_HUGEPAGES(2)
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