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free_hugepages.html
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<!-- Creator : groff version 1.22.4 -->
<!-- CreationDate: Wed Jan 29 11:27:09 2020 -->
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="generator" content="groff -Thtml, see www.gnu.org">
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<meta name="Content-Style" content="text/css">
<style type="text/css">
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h1 { text-align: center }
</style>
<title>ALLOC_HUGEPAGES</title>
</head>
<body>
<h1 align="center">ALLOC_HUGEPAGES</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#RETURN VALUE">RETURN VALUE</a><br>
<a href="#ERRORS">ERRORS</a><br>
<a href="#FILES">FILES</a><br>
<a href="#CONFORMING TO">CONFORMING TO</a><br>
<a href="#NOTES">NOTES</a><br>
<a href="#COLOPHON">COLOPHON</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">alloc_hugepages,
free_hugepages - allocate or free huge pages</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>void
*alloc_hugepages(int</b> <i>key</i><b>, void
*</b><i>addr</i><b>, size_t</b> <i>len</i><b>, <br>
int</b> <i>prot</i><b>, int</b> <i>flag</i><b>);</b></p>
<p style="margin-left:11%; margin-top: 1em"><b>int
free_hugepages(void *</b><i>addr</i><b>);</b></p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">The system
calls <b>alloc_hugepages</b>() and <b>free_hugepages</b>()
were introduced in Linux 2.5.36 and removed again in 2.5.54.
They existed only on i386 and ia64 (when built with
<b>CONFIG_HUGETLB_PAGE</b>). In Linux 2.4.20, the syscall
numbers exist, but the calls fail with the error
<b>ENOSYS</b>.</p>
<p style="margin-left:11%; margin-top: 1em">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.</p>
<p style="margin-left:11%; margin-top: 1em">The <i>key</i>
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 <i>key</i>,
and inherited by child processes.</p>
<p style="margin-left:11%; margin-top: 1em">The <i>addr</i>
argument of <b>free_hugepages</b>() tells which page is
being freed: it was the return value of a call to
<b>alloc_hugepages</b>(). (The memory is first actually
freed when all users have released it.) The <i>addr</i>
argument of <b>alloc_hugepages</b>() is a hint, that the
kernel may or may not follow. Addresses must be properly
aligned.</p>
<p style="margin-left:11%; margin-top: 1em">The <i>len</i>
argument is the length of the required segment. It must be a
multiple of the huge page size.</p>
<p style="margin-left:11%; margin-top: 1em">The <i>prot</i>
argument specifies the memory protection of the segment. It
is one of <b>PROT_READ</b>, <b>PROT_WRITE</b>,
<b>PROT_EXEC</b>.</p>
<p style="margin-left:11%; margin-top: 1em">The <i>flag</i>
argument is ignored, unless <i>key</i> is positive. In that
case, if <i>flag</i> is <b>IPC_CREAT</b>, then a new huge
page segment is created when none with the given key
existed. If this flag is not set, then <b>ENOENT</b> is
returned when no segment with the given key exists.</p>
<h2>RETURN VALUE
<a name="RETURN VALUE"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">On success,
<b>alloc_hugepages</b>() returns the allocated virtual
address, and <b>free_hugepages</b>() returns zero. On error,
-1 is returned, and <i>errno</i> is set appropriately.</p>
<h2>ERRORS
<a name="ERRORS"></a>
</h2>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em"><b>ENOSYS</b></p></td>
<td width="2%"></td>
<td width="73%">
<p style="margin-top: 1em">The system call is not supported
on this kernel.</p></td>
<td width="5%">
</td></tr>
</table>
<h2>FILES
<a name="FILES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><i>/proc/sys/vm/nr_hugepages</i></p>
<p style="margin-left:22%;">Number of configured hugetlb
pages. This can be read and written.</p>
<p style="margin-left:11%;"><i>/proc/meminfo</i></p>
<p style="margin-left:22%;">Gives info on the number of
configured hugetlb pages and on their size in the three
variables HugePages_Total, HugePages_Free, Hugepagesize.</p>
<h2>CONFORMING TO
<a name="CONFORMING TO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">These calls are
specific to Linux on Intel processors, and should not be
used in programs intended to be portable.</p>
<h2>NOTES
<a name="NOTES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">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 <b>mmap</b>(2) to map files in this
virtual filesystem.</p>
<p style="margin-left:11%; margin-top: 1em">The maximal
number of huge pages can be specified using the
<b>hugepages=</b> boot parameter.</p>
<h2>COLOPHON
<a name="COLOPHON"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">This page is
part of release 5.02 of the Linux <i>man-pages</i> 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/.</p>
<hr>
</body>
</html>