Originální popis anglicky:
alloc_hugepages, free_hugepages - allocate or free huge pages
Návod, kniha: Linux Programmer's Manual
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 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 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.
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.
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 programs 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.
/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.
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.
