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version 1.1, 2016/12/29 16:54:37 version 1.3, 2016/12/29 17:02:27
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 # [[!template id=man name=uvm_hotplug section=9]] port-masters' FAQ.  # [[!template id=man name=uvm_hotplug section=9]] port-masters' FAQ.
   
 1. Why does it matter?    1. Why does it matter?
   
 As a port maintainer any architecture that needs to use the virtual memory       As a port maintainer any architecture that needs to use the virtual memory
 sub-system of NetBSD aka uvm is affected by the       sub-system of NetBSD aka uvm is affected by the
 [[!template id=man name=uvm_hotplug section=9]] change.       [[!template id=man name=uvm_hotplug section=9]] change.
   
 Early boot code of every port is affected. Global variables:       Early boot code of every port is affected. Global variables:
 struct vm_physseg vm_physmem;  
 int vm_nphysmem;  
 are no longer visible. They need to be replaced by appropriate  
 accessor calls in [[!template id=man name=uvm_hotplug section=9]]  
   
 These calls are documented as "Utility Functions" in the             struct vm_physseg vm_physmem;
 [[!template id=man name=uvm_hotplug section=9]] manual.             int vm_nphysmem;
   
        are no longer visible. They need to be replaced by appropriate
        accessor calls in [[!template id=man name=uvm_hotplug section=9]]
   
 The "switchover" CVS commit log is here:       These calls are documented as "Utility Functions" in the
 [http://mail-index.netbsd.org/source-changes/2016/12/23/msg080110.html](http://mail-index.netbsd.org/source-changes/2016/12/23/msg080110.html)       [[!template id=man name=uvm_hotplug section=9]] manual.
   
        The "switchover" CVS commit log is here:
        [http://mail-index.netbsd.org/source-changes/2016/12/23/msg080110.html](http://mail-index.netbsd.org/source-changes/2016/12/23/msg080110.html)
   
 2. What files may be affected?    2. What files may be affected?
   
 In most of the architectures the "sys/arch/<arch_name>/<arch_name>/machdep.c"       In most of the architectures the "sys/arch/<arch_name>/<arch_name>/machdep.c"
 and "sys/arch/<arch_name>/<arch_name>/pmap.c" if they exist are usually       and "sys/arch/<arch_name>/<arch_name>/pmap.c" if they exist are usually
 affected.       affected.
   
 But this may not be a exhaustive list. Any other files that deals with pmap and       But this may not be a exhaustive list. Any other files that deals with pmap and
 stealing pages might also be affected.       stealing pages might also be affected.
   
 3. What does it do ?    3. What does it do ?
   
 [[!template id=man name=uvm_hotplug section=9]] manages the previously exposed "vm_physmem" static array which       [[!template id=man name=uvm_hotplug section=9]] manages the previously exposed "vm_physmem" static array which
 used to keep track of the memory segments.       used to keep track of the memory segments.
   
 In the current implementation, the array has been replaced with a       In the current implementation, the array has been replaced with a
 [[!template id=man name=rbtree section=3]] backing which makes the       [[!template id=man name=rbtree section=3]] backing which makes the
 data structure dynamic.       data structure dynamic.
   
 An array based implementation is also provided, for backwards       An array based implementation is also provided, for backwards
 compatibility. This is the default implementation and does not provide       compatibility. This is the default implementation and does not provide
 hot pluggability. It is also used without 'options UVM_HOTPLUG'       hot pluggability. It is also used without 'options UVM_HOTPLUG'
 However the API itself is implementation agnostic.       However the API itself is implementation agnostic.
   
 4. Why is it needed?    4. Why is it needed?
   
 With the [[!template id=man name=rbtree section=3]] backing       With the [[!template id=man name=rbtree section=3]] backing
 implementation, the list of physical pages        implementation, the list of physical pages 
 in the system is no longer in a static array and can dynamically       in the system is no longer in a static array and can dynamically
 expand or collapse, hence adding new pages to the freelist from newly       expand or collapse, hence adding new pages to the freelist from newly
 available RAM / physical memory (plug) or removing retired pages       available RAM / physical memory (plug) or removing retired pages
 (unplug) via taking them off the freelist and the old vm_physmem.       (unplug) via taking them off the freelist and the old vm_physmem.
   
 5. What should I do?    5. What should I do?
   
 Review the changes to your port due to this new feature. The changes       Review the changes to your port due to this new feature. The changes
 may have been made without direct knowledge of your port architecture.       may have been made without direct knowledge of your port architecture.
   
 See if your port has hotpluggable hardware. If it does, write a driver       See if your port has hotpluggable hardware. If it does, write a driver
 to use the [[!template id=man name=uvm_hotplug section=9]] api.       to use the [[!template id=man name=uvm_hotplug section=9]] api.
   
 An example of [[!template id=man name=uvm_hotplug section=9]] api's  
 application can be found in  
 [[!template id=man name=balloon section=4]].  
   
        An example of [[!template id=man name=uvm_hotplug section=9]] api's
        application can be found in
        [[!template id=man name=balloon section=4]].
   
Removed from v.1.1  
changed lines
  Added in v.1.3

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