NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | FILES | CONFORMING TO | NOTES | COLOPHON
ALLOC_HUGEPAGES(2) Linux Programmer's Manual ALLOC_HUGEPAGES(2)
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 file system 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 file system.
The maximal number of huge pages can be specified using the hugepages= boot
parameter.
This page is part of release 3.23 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)