209 lines
4.7 KiB
HTML
209 lines
4.7 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 POSIX_MADVISE</TITLE>
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</HEAD><BODY>
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<H1>POSIX_MADVISE</H1>
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Section: Linux Programmer's Manual (3)<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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posix_madvise - give advice about patterns of memory usage
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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>#include <<A HREF="file:///usr/include/sys/mman.h">sys/mman.h</A>></B>
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<B>int posix_madvise(void *</B><I>addr</I><B>, size_t </B><I>len</I><B>, int </B><I>advice</I><B>);</B>
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</PRE>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>posix_madvise</B>():
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<BR>
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<DL COMPACT><DT id="1"><DD>
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_POSIX_C_SOURCE >= 200112L
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>posix_madvise</B>()
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function allows an application to advise the system about its expected
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patterns of usage of memory in the address range starting at
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<I>addr</I>
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and continuing for
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<I>len</I>
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bytes.
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The system is free to use this advice in order to improve the performance
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of memory accesses (or to ignore the advice altogether), but calling
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<B>posix_madvise</B>()
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shall not affect the semantics of access to memory in the specified range.
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<P>
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The
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<I>advice</I>
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argument is one of the following:
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<DL COMPACT>
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<DT id="2"><B>POSIX_MADV_NORMAL</B>
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<DD>
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The application has no special advice regarding its memory usage patterns
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for the specified address range.
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This is the default behavior.
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<DT id="3"><B>POSIX_MADV_SEQUENTIAL</B>
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<DD>
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The application expects to access the specified address range sequentially,
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running from lower addresses to higher addresses.
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Hence, pages in this region can be aggressively read ahead,
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and may be freed soon after they are accessed.
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<DT id="4"><B>POSIX_MADV_RANDOM</B>
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<DD>
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The application expects to access the specified address range randomly.
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Thus, read ahead may be less useful than normally.
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<DT id="5"><B>POSIX_MADV_WILLNEED</B>
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<DD>
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The application expects to access the specified address range
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in the near future.
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Thus, read ahead may be beneficial.
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<DT id="6"><B>POSIX_MADV_DONTNEED</B>
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<DD>
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The application expects that it will not access the specified address range
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in the near future.
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</DL>
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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>posix_madvise</B>()
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returns 0.
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On failure, it returns a positive error number.
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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="7"><B>EINVAL</B>
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<DD>
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<I>addr</I>
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is not a multiple of the system page size or
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<I>len</I>
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is negative.
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<DT id="8"><B>EINVAL</B>
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<DD>
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<I>advice</I>
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is invalid.
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<DT id="9"><B>ENOMEM</B>
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<DD>
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Addresses in the specified range are partially or completely outside
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the caller's address space.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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Support for
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<B>posix_madvise</B>()
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first appeared in glibc version 2.2.
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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POSIX.1 permits an implementation to generate an error if
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<I>len</I>
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is 0.
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On Linux, specifying
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<I>len</I>
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as 0 is permitted (as a successful no-op).
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<P>
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In glibc, this function is implemented using
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<B><A HREF="/cgi-bin/man/man2html?2+madvise">madvise</A></B>(2).
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However, since glibc 2.6,
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<B>POSIX_MADV_DONTNEED</B>
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is treated as a no-op, because the corresponding
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<B><A HREF="/cgi-bin/man/man2html?2+madvise">madvise</A></B>(2)
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value,
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<B>MADV_DONTNEED</B>,
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has destructive semantics.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+madvise">madvise</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+posix_fadvise">posix_fadvise</A></B>(2)
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<A NAME="lbAK"> </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="10"><A HREF="#lbAB">NAME</A><DD>
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<DT id="11"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="12"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="13"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="14"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="15"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="16"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="17"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="18"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="19"><A HREF="#lbAK">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: 00:05:52 GMT, March 31, 2021
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