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' memory or to
free them again. Huge pages are locked into memory, 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
processes.
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.
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 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.
Copyright 2003 Andries E. Brouwer (aeb@cwi.nl)
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