.\" Copyright 2003 Andries E. Brouwer (aeb@cwi.nl)

.\"

.\" %%%LICENSE_START(VERBATIM)

.\" Permission is granted to make and distribute verbatim copies of this

.\" manual provided the copyright notice and this permission notice are

.\" preserved on all copies.

.\"

.\" Permission is granted to copy and distribute modified versions of this

.\" manual under the conditions for verbatim copying, provided that the

.\" entire resulting derived work is distributed under the terms of a

.\" permission notice identical to this one.

.\"

.\" Since the Linux kernel and libraries are constantly changing, this

.\" manual page may be incorrect or out-of-date.  The author(s) assume no

.\" responsibility for errors or omissions, or for damages resulting from

.\" the use of the information contained herein.  The author(s) may not

.\" have taken the same level of care in the production of this manual,

.\" which is licensed free of charge, as they might when working

.\" professionally.

.\"

.\" Formatted or processed versions of this manual, if unaccompanied by

.\" the source, must acknowledge the copyright and authors of this work.

.\" %%%LICENSE_END

.\"

.TH ALLOC_HUGEPAGES 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

alloc_hugepages, free_hugepages \- allocate or free huge pages

.SH SYNOPSIS

.nf

.BI "void *alloc_hugepages(int " key ", void *" addr ", size_t " len ,

.BI "                      int " prot ", int " flag );

.\" asmlinkage unsigned long sys_alloc_hugepages(int key, unsigned long addr,

.\" unsigned long len, int prot, int flag);

.PP

.BI "int free_hugepages(void *" addr );

.\" asmlinkage int sys_free_hugepages(unsigned long addr);

.fi

.SH DESCRIPTION

The system calls

.BR alloc_hugepages ()

and

.BR 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

.BR CONFIG_HUGETLB_PAGE ).

In Linux 2.4.20, the syscall numbers exist,

but the calls fail with the error

.BR ENOSYS .

.PP

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.

.PP

The

.I 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

.IR key ,

and inherited by child processes.

.PP

The

.I addr

argument of

.BR free_hugepages ()

tells which page is being freed: it was the return value of a

call to

.BR alloc_hugepages ().

(The memory is first actually freed when all users have released it.)

The

.I addr

argument of

.BR alloc_hugepages ()

is a hint, that the kernel may or may not follow.

Addresses must be properly aligned.

.PP

The

.I len

argument is the length of the required segment.

It must be a multiple of the huge page size.

.PP

The

.I prot

argument specifies the memory protection of the segment.

It is one of

.BR PROT_READ ,

.BR PROT_WRITE ,

.BR PROT_EXEC .

.PP

The

.I flag

argument is ignored, unless

.I key

is positive.

In that case, if

.I flag

is

.BR IPC_CREAT ,

then a new huge page segment is created when none

with the given key existed.

If this flag is not set, then

.B ENOENT

is returned when no segment with the given key exists.

.SH RETURN VALUE

On success,

.BR alloc_hugepages ()

returns the allocated virtual address, and

.BR free_hugepages ()

returns zero.

On error, \-1 is returned, and

.I errno

is set appropriately.

.SH ERRORS

.TP

.B ENOSYS

The system call is not supported on this kernel.

.SH FILES

.TP

.I /proc/sys/vm/nr_hugepages

Number of configured hugetlb pages.

This can be read and written.

.TP

.I /proc/meminfo

Gives info on the number of configured hugetlb pages and on their size

in the three variables HugePages_Total, HugePages_Free, Hugepagesize.

.SH CONFORMING TO

These calls are specific to Linux on Intel processors, and should not be

used in programs intended to be portable.

.SH 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

.BR mmap (2)

to map files in this virtual filesystem.

.PP

The maximal number of huge pages can be specified using the

.B hugepages=

boot parameter.

.PP

.\" requires CONFIG_HUGETLB_PAGE (under "Processor type and features")

.\" and CONFIG_HUGETLBFS (under "Filesystems").

.\" mount -t hugetlbfs hugetlbfs /huge

.\" SHM_HUGETLB

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.