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ALLOC_HUGEPAGES
Section: Linux Programmer's Manual (2)
Updated: 2007-05-31
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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);
int free_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 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.
RETURN VALUE
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.
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.
CONFORMING TO
These calls are specific to Linux on Intel processors, and should not be
used in programs intended to be portable.
NOTES
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.
COLOPHON
This page is part of release 3.05 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- FILES
-
- CONFORMING TO
-
- NOTES
-
- COLOPHON
-
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