223 lines
4.8 KiB
HTML
223 lines
4.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of ALLOC_HUGEPAGES</TITLE>
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</HEAD><BODY>
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<H1>ALLOC_HUGEPAGES</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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alloc_hugepages, free_hugepages - allocate or free huge pages
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>void *alloc_hugepages(int </B><I>key</I><B>, void *</B><I>addr</I><B>, size_t </B><I>len</I><B>,</B>
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<B> int </B><I>prot</I><B>, int </B><I>flag</I><B>);</B>
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<B>int free_hugepages(void *</B><I>addr</I><B>);</B>
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The system calls
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<B>alloc_hugepages</B>()
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and
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<B>free_hugepages</B>()
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were introduced in Linux 2.5.36 and removed again in 2.5.54.
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They existed only on i386 and ia64 (when built with
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<B>CONFIG_HUGETLB_PAGE</B>).
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In Linux 2.4.20, the syscall numbers exist,
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but the calls fail with the error
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<B>ENOSYS</B>.
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<P>
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On i386 the memory management hardware knows about ordinary pages (4 KiB)
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and huge pages (2 or 4 MiB).
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Similarly ia64 knows about huge pages of
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several sizes.
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These system calls serve to map huge pages into the
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process's memory or to free them again.
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Huge pages are locked into memory, and are not swapped.
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<P>
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The
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<I>key</I>
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argument is an identifier.
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When zero the pages are private, and
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not inherited by children.
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When positive the pages are shared with other applications using the same
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<I>key</I>,
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and inherited by child processes.
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<P>
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The
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<I>addr</I>
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argument of
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<B>free_hugepages</B>()
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tells which page is being freed: it was the return value of a
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call to
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<B>alloc_hugepages</B>().
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(The memory is first actually freed when all users have released it.)
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The
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<I>addr</I>
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argument of
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<B>alloc_hugepages</B>()
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is a hint, that the kernel may or may not follow.
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Addresses must be properly aligned.
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<P>
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The
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<I>len</I>
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argument is the length of the required segment.
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It must be a multiple of the huge page size.
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<P>
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The
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<I>prot</I>
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argument specifies the memory protection of the segment.
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It is one of
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<B>PROT_READ</B>,
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<B>PROT_WRITE</B>,
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<B>PROT_EXEC</B>.
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<P>
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The
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<I>flag</I>
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argument is ignored, unless
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<I>key</I>
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is positive.
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In that case, if
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<I>flag</I>
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is
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<B>IPC_CREAT</B>,
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then a new huge page segment is created when none
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with the given key existed.
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If this flag is not set, then
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<B>ENOENT</B>
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is returned when no segment with the given key exists.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success,
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<B>alloc_hugepages</B>()
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returns the allocated virtual address, and
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<B>free_hugepages</B>()
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returns zero.
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On error, -1 is returned, and
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<I>errno</I>
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is set appropriately.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="1"><B>ENOSYS</B>
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<DD>
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The system call is not supported on this kernel.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>FILES</H2>
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<DL COMPACT>
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<DT id="2"><I>/proc/sys/vm/nr_hugepages</I>
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<DD>
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Number of configured hugetlb pages.
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This can be read and written.
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<DT id="3"><I>/proc/meminfo</I>
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<DD>
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Gives info on the number of configured hugetlb pages and on their size
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in the three variables HugePages_Total, HugePages_Free, Hugepagesize.
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</DL>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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These calls are specific to Linux on Intel processors, and should not be
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used in programs intended to be portable.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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These system calls are gone;
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they existed only in Linux 2.5.36 through to 2.5.54.
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Now the hugetlbfs filesystem can be used instead.
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Memory backed by huge pages (if the CPU supports them) is obtained by
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using
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2)
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to map files in this virtual filesystem.
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<P>
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The maximal number of huge pages can be specified using the
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<B>hugepages=</B>
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boot parameter.
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<P>
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<A NAME="lbAJ"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="4"><A HREF="#lbAB">NAME</A><DD>
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<DT id="5"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="6"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="7"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="8"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="9"><A HREF="#lbAG">FILES</A><DD>
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<DT id="10"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="11"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="12"><A HREF="#lbAJ">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:32 GMT, March 31, 2021
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</BODY>
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