osfmk/man/vm_behavior_set.html

   1 <h2>vm_behavior_set</h2>
   2 <hr>
   3 <p>
   4 <strong>Function</strong> - Specify expected access patterns for the target VM region.
   5 <h3>SYNOPSIS</h3>
   6 <pre>
   7 <strong>kern_return_t   vm_behavior_set</strong>
   8                 <strong>(vm_task_t</strong>                          <var>target_task</var>,
   9                  <strong>vm_address_t</strong>                           <var>address</var>,
  10                  <strong>vm_size_t</strong>                                 <var>size</var>,
  11                  <strong>vm_behavior_t</strong>                         <var>behavior</var><strong>);</strong>
  12 </pre>
  13 <h3>PARAMETERS</h3>
  14 <dl>
  15 <p>
  16 <dt> <var>target_task</var>
  17 <dd>
  18 [in task send right]
  19 The port for the task in whose address space the
  20 memory object behavior is to be set.
  21 <p>
  22 <dt> <var>address</var>
  23 <dd>
  24 [in scalar]
  25 The starting address for the memory region.
  26 <p>
  27 <dt> <var>size</var>
  28 <dd>
  29 [in scalar]
  30 The number of bytes in the region.
  31 <p>
  32 <dt> <var>behavior</var>
  33 <dd>
  34 [in scalar]
  35 The expected reference pattern for the memory.  Possible
  36 values are:
  37 <dl>
  38 <p>
  39 <dt> <strong>VM_BEHAVIOR_DEFAULT</strong>
  40 <dd>
  41 The system's default behavior.  Assumes strong locality of
  42 reference, so LRU page replacement, possibly with pre-fetch,
  43 would be appropriate.
  44 <p>
  45 <dt> <strong>VM_BEHAVIOR_RANDOM</strong>
  46 <dd>
  47 No particular order expected.  Assumes weak locality of
  48 reference, so LRU page replacement may be ineffective.
  49 <p>
  50 <dt> <strong>VM_BEHAVIOR_SEQUENTIAL</strong>
  51 <dd>
  52 Forward sequential order.
  53 <p>
  54 <dt> <strong>VM_BEHAVIOR_RSEQNTL</strong>
  55 <dd>
  56 Reverse sequential order.
  57 </dl>
  58 </dl>
  59 <h3>DESCRIPTION</h3>
  60 <p>
  61 The <strong>vm_behavior_set</strong> function informs the kernel of
  62 the expected access
  63 pattern for a region of memory.  The kernel uses this information
  64 to bias its prefetch and page
  65 replacement algorithms.
  66 <p>
  67 The region starts at the beginning of the virtual page containing
  68 <var>address</var>; it ends at the end of the virtual page containing
  69 <var>address</var> + <var>size</var> - 1.  Because of this
  70 rounding to virtual page boundaries, the amount of memory affected may be
  71 greater than <var>size</var>.  Use <strong>host_page_size</strong>
  72 to find the current virtual page size.
  73 <h3>NOTES</h3>
  74 <p>
  75 This interface is machine word length specific because of the virtual address
  76 parameter.
  77 <h3>RETURN VALUES</h3>
  78 <dl>
  79 <p>
  80 <dt> <strong>KERN_INVALID_ADDRESS</strong>
  81 <dd>
  82 The specified address is illegal or reserved.
  83 </dl>
  84 <h3>RELATED INFORMATION</h3>
  85 <p>
  86 Functions:
  87 <a href="vm_region.html"><strong>vm_region</strong></a>,
  88 <a href="host_page_size.html"><strong>host_page_size</strong></a>.