ALLOC_HUGEPAGES(2) Linux Programmer's Manual ALLOC_HUGEPAGES(2)
NAME
alloc_hugepages, free_hugepages - allocate or free huge pages
SYNOPSIS
void*alloc_hugepages(int key,void*addr,size_t len,int prot,int
flag);
intfree_hugepages(void*addr);
DESCRIPTION
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 mem-
ory, 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 pro-
cesses.
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.
RETURNVALUE
On success, alloc_hugepages returns the allocated virtual address, and
free_hugepages returns zero. On error, -1 is returned, and errno is set
appropriately.
ERRORS
ENOSYS The system call is not supported on this kernel.
CONFORMINGTO
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 pro-
grams 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.
FILES
/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.
NOTES
The system calls are gone. Now the hugetlbfs filesystem can be used
instead. Memory backed by huge pages (if the CPU supports them) is
obtained by mmap'ing files in this virtual filesystem.
The maximal number of huge pages can be specified using the hugepages=
boot parameter.
Linux 2.5.36 2003-02-02 ALLOC_HUGEPAGES(2)
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