384 lines
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384 lines
7.4 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of GET_MEMPOLICY</TITLE>
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</HEAD><BODY>
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<H1>GET_MEMPOLICY</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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get_mempolicy - retrieve NUMA memory policy for a thread
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/numaif.h">numaif.h</A>></B>
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<PRE>
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<B>long get_mempolicy(int *</B><I>mode</I><B>, unsigned long *</B><I>nodemask</I><B>,</B>
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<B> unsigned long </B><I>maxnode</I><B>, void *</B><I>addr</I><B>,</B>
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<B> unsigned long </B><I>flags</I><B>);</B>
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Link with <I>-lnuma</I>.
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>get_mempolicy</B>()
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retrieves the NUMA policy of the calling thread or of a memory address,
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depending on the setting of
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<I>flags</I>.
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<P>
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A NUMA machine has different
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memory controllers with different distances to specific CPUs.
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The memory policy defines from which node memory is allocated for
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the thread.
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<P>
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If
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<I>flags</I>
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is specified as 0,
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then information about the calling thread's default policy
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(as set by
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<B><A HREF="/cgi-bin/man/man2html?2+set_mempolicy">set_mempolicy</A></B>(2))
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is returned, in the buffers pointed to by
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<I>mode</I>
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and
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<I>nodemask</I>.
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The value returned in these arguments
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may be used to restore the thread's policy to its state at
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the time of the call to
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<B>get_mempolicy</B>()
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using
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<B><A HREF="/cgi-bin/man/man2html?2+set_mempolicy">set_mempolicy</A></B>(2).
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When
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<I>flags</I>
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is 0,
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<I>addr</I>
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must be specified as NULL.
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<P>
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If
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<I>flags</I>
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specifies
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<B>MPOL_F_MEMS_ALLOWED</B>
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(available since Linux 2.6.24), the
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<I>mode</I>
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argument is ignored and the set of nodes (memories) that the
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thread is allowed to specify in subsequent calls to
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<B><A HREF="/cgi-bin/man/man2html?2+mbind">mbind</A></B>(2)
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or
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<B><A HREF="/cgi-bin/man/man2html?2+set_mempolicy">set_mempolicy</A></B>(2)
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(in the absence of any
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<I>mode flags</I>)
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is returned in
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<I>nodemask</I>.
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It is not permitted to combine
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<B>MPOL_F_MEMS_ALLOWED</B>
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with either
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<B>MPOL_F_ADDR</B>
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or
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<B>MPOL_F_NODE</B>.
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<P>
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If
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<I>flags</I>
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specifies
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<B>MPOL_F_ADDR</B>,
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then information is returned about the policy governing the memory
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address given in
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<I>addr</I>.
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This policy may be different from the thread's default policy if
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<B><A HREF="/cgi-bin/man/man2html?2+mbind">mbind</A></B>(2)
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or one of the helper functions described in
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<B><A HREF="/cgi-bin/man/man2html?3+numa">numa</A></B>(3)
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has been used to establish a policy for the memory range containing
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<I>addr</I>.
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<P>
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If the
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<I>mode</I>
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argument is not NULL, then
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<B>get_mempolicy</B>()
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will store the policy mode and any optional
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<I>mode flags</I>
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of the requested NUMA policy in the location pointed to by this argument.
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If
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<I>nodemask</I>
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is not NULL, then the nodemask associated with the policy will be stored
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in the location pointed to by this argument.
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<I>maxnode</I>
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specifies the number of node IDs
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that can be stored into
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<I>nodemask</I>---that
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is, the maximum node ID plus one.
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The value specified by
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<I>maxnode</I>
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is always rounded to a multiple of
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<I>sizeof(unsigned long)*8</I>.
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<P>
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If
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<I>flags</I>
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specifies both
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<B>MPOL_F_NODE</B>
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and
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<B>MPOL_F_ADDR</B>,
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<B>get_mempolicy</B>()
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will return the node ID of the node on which the address
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<I>addr</I>
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is allocated into the location pointed to by
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<I>mode</I>.
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If no page has yet been allocated for the specified address,
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<B>get_mempolicy</B>()
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will allocate a page as if the thread had performed a read
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(load) access to that address, and return the ID of the node
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where that page was allocated.
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<P>
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If
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<I>flags</I>
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specifies
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<B>MPOL_F_NODE</B>,
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but not
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<B>MPOL_F_ADDR</B>,
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and the thread's current policy is
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<B>MPOL_INTERLEAVE</B>,
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then
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<B>get_mempolicy</B>()
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will return in the location pointed to by a non-NULL
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<I>mode</I>
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argument,
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the node ID of the next node that will be used for
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interleaving of internal kernel pages allocated on behalf of the thread.
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These allocations include pages for memory-mapped files in
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process memory ranges mapped using the
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2)
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call with the
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<B>MAP_PRIVATE</B>
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flag for read accesses, and in memory ranges mapped with the
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<B>MAP_SHARED</B>
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flag for all accesses.
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<P>
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Other flag values are reserved.
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<P>
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For an overview of the possible policies see
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<B><A HREF="/cgi-bin/man/man2html?2+set_mempolicy">set_mempolicy</A></B>(2).
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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>get_mempolicy</B>()
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returns 0;
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on error, -1 is returned and
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<I>errno</I>
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is set to indicate the error.
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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>EFAULT</B>
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<DD>
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Part of all of the memory range specified by
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<I>nodemask</I>
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and
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<I>maxnode</I>
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points outside your accessible address space.
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<DT id="2"><B>EINVAL</B>
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<DD>
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The value specified by
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<I>maxnode</I>
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is less than the number of node IDs supported by the system.
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Or
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<I>flags</I>
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specified values other than
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<B>MPOL_F_NODE</B>
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or
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<B>MPOL_F_ADDR</B>;
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or
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<I>flags</I>
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specified
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<B>MPOL_F_ADDR</B>
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and
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<I>addr</I>
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is NULL,
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or
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<I>flags</I>
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did not specify
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<B>MPOL_F_ADDR</B>
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and
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<I>addr</I>
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is not NULL.
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Or,
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<I>flags</I>
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specified
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<B>MPOL_F_NODE</B>
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but not
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<B>MPOL_F_ADDR</B>
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and the current thread policy is not
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<B>MPOL_INTERLEAVE</B>.
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Or,
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<I>flags</I>
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specified
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<B>MPOL_F_MEMS_ALLOWED</B>
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with either
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<B>MPOL_F_ADDR</B>
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or
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<B>MPOL_F_NODE</B>.
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(And there are other
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<B>EINVAL</B>
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cases.)
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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The
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<B>get_mempolicy</B>()
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system call was added to the Linux kernel in version 2.6.7.
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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This system call is Linux-specific.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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For information on library support, see
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<B><A HREF="/cgi-bin/man/man2html?7+numa">numa</A></B>(7).
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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+getcpu">getcpu</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+mbind">mbind</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+set_mempolicy">set_mempolicy</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?3+numa">numa</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+numa">numa</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?8+numactl">numactl</A></B>(8)
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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="3"><A HREF="#lbAB">NAME</A><DD>
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<DT id="4"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="5"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="6"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="7"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="8"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="9"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="10"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="11"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="12"><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: 00:05:32 GMT, March 31, 2021
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