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  • Committer: Suren A. Chilingaryan
  • Date: 2009-04-09 03:21:08 UTC
  • Revision ID: csa@dside.dyndns.org-20090409032108-w4edamdh4adrgdu3
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Administration/Linux/system/memory/Malloc-Tunable-Parameters.html
 
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<html lang="en"><head><title>Malloc Tunable Parameters - The GNU C Library</title>
 
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<p>
 
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<a name="Malloc-Tunable-Parameters"></a>
 
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Next:&nbsp;<a rel="next" accesskey="n" href="http://www.gnu.org/software/libc/manual/html_node/Heap-Consistency-Checking.html#Heap-Consistency-Checking">Heap Consistency Checking</a>,
 
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Previous:&nbsp;<a rel="previous" accesskey="p" href="http://www.gnu.org/software/libc/manual/html_node/Aligned-Memory-Blocks.html#Aligned-Memory-Blocks">Aligned Memory Blocks</a>,
 
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Up:&nbsp;<a rel="up" accesskey="u" href="http://www.gnu.org/software/libc/manual/html_node/Unconstrained-Allocation.html#Unconstrained-Allocation">Unconstrained Allocation</a>
 
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</p><hr>
 
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</div>
 
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<h5 class="subsubsection">3.2.2.8 Malloc Tunable Parameters</h5>
 
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<p>You can adjust some parameters for dynamic memory allocation with the
 
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<code>mallopt</code> function.  This function is the general SVID/XPG
 
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interface, defined in <samp><span class="file">malloc.h</span></samp>. 
 
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<a name="index-malloc_002eh-269"></a>
 
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</p><div class="defun">
 
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&#8212; Function: int <b>mallopt</b> (<var>int param, int value</var>)<var><a name="index-mallopt-270"></a></var><br>
 
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<blockquote><p>When calling <code>mallopt</code>, the <var>param</var> argument specifies the
 
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parameter to be set, and <var>value</var> the new value to be set.  Possible
 
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choices for <var>param</var>, as defined in <samp><span class="file">malloc.h</span></samp>, are:
 
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          </p><dl>
 
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<dt><code>M_TRIM_THRESHOLD</code></dt><dd>This is the minimum size (in bytes) of the top-most, releasable chunk
 
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that will cause <code>sbrk</code> to be called with a negative argument in
 
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order to return memory to the system. 
 
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<br></dd><dt><code>M_TOP_PAD</code></dt><dd>This parameter determines the amount of extra memory to obtain from the
 
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system when a call to <code>sbrk</code> is required.  It also specifies the
 
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number of bytes to retain when shrinking the heap by calling <code>sbrk</code>
 
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with a negative argument.  This provides the necessary hysteresis in
 
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heap size such that excessive amounts of system calls can be avoided. 
 
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<br></dd><dt><code>M_MMAP_THRESHOLD</code></dt><dd>All chunks larger than this value are allocated outside the normal
 
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heap, using the <code>mmap</code> system call.  This way it is guaranteed
 
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that the memory for these chunks can be returned to the system on
 
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<code>free</code>. 
 
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<br></dd><dt><code>M_MMAP_MAX</code></dt><dd>The maximum number of chunks to allocate with <code>mmap</code>.  Setting this
 
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to zero disables all use of <code>mmap</code>. 
 
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</dd></dl>
 
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        </blockquote></div>
 
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</body></html>
 
 
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