alloc_hugepages
Section: System Calls (2)
Updated: 202-0-08
Index
Return to Main Contents
NAME
alloc_hugepages, free_hugepages - allocate or free huge pages
SYNOPSIS
void *syscall(size_t size;
SYS_alloc_hugepages, int key,
void addr[size], size_t size,
int prot, int flag);
int syscall(SYS_free_hugepages, void *addr);
Note:
glibc provides no wrappers for these system calls,
necessitating the use of
syscall(2).
DESCRIPTION
The system calls
alloc_hugepages()
and
free_hugepages()
were introduced in Linux 2.5.36 and removed again in Linux 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
size
argument is the size 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 to indicate the error.
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.
STANDARDS
Linux on Intel processors.
HISTORY
These system calls are gone;
they existed only in Linux 2.5.36 through to Linux 2.5.54.
NOTES
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.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- FILES
-
- STANDARDS
-
- HISTORY
-
- NOTES
-
|
|
- Running on 
-
:
