alloc_hugepages(2) -- Linux man page
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 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.
.SHRETURN 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.
CONFORMING TO
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.
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.
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