alloc_hugepages(2) System Calls Manual alloc_hugepages(2)
NAME
alloc_hugepages, free_hugepages - allocate or free huge pages
SYNOPSIS
void *syscall(SYS_alloc_hugepages, int key, void addr[.len], size_t len,
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 argu-
ment 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 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 writ-
ten.
/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.
Linux man-pages 6.7 2023-10-31 alloc_hugepages(2)
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