+.. _admin_guide_memory_hotplug:
+
==============
Memory Hotplug
==============
Because Memory Hotplug is still under development, contents of this text will
be changed often.
+.. contents:: :local:
+
.. CONTENTS
1. Introduction
- 1.1 purpose of memory hotplug
+ 1.1 Purpose of memory hotplug
1.2. Phases of memory hotplug
1.3. Unit of Memory online/offline operation
2. Kernel Configuration
(1) x86_64's has special implementation for memory hotplug.
This text does not describe it.
- (2) This text assumes that sysfs is mounted at /sys.
+ (2) This text assumes that sysfs is mounted at ``/sys``.
Introduction
============
-purpose of memory hotplug
+Purpose of memory hotplug
-------------------------
Memory Hotplug allows users to increase/decrease the amount of memory.
Linux memory hotplug is designed for both purpose.
-
Phases of memory hotplug
------------------------
(However, if you writes udev's hotplug scripts for memory hotplug, these
phases can be execute in seamless way.)
-
Unit of Memory online/offline operation
---------------------------------------
default size of a memory block is the same as memory section size unless an
architecture specifies otherwise. (see :ref:`memory_hotplug_sysfs_files`.)
-To determine the size (in bytes) of a memory block please read this file:
-
-/sys/devices/system/memory/block_size_bytes
+To determine the size (in bytes) of a memory block please read this file::
+ /sys/devices/system/memory/block_size_bytes
Kernel Configuration
====================
config options.
- For all memory hotplug:
- - Memory model -> Sparse Memory (CONFIG_SPARSEMEM)
- - Allow for memory hot-add (CONFIG_MEMORY_HOTPLUG)
+ - Memory model -> Sparse Memory (``CONFIG_SPARSEMEM``)
+ - Allow for memory hot-add (``CONFIG_MEMORY_HOTPLUG``)
- To enable memory removal, the following are also necessary:
- - Allow for memory hot remove (CONFIG_MEMORY_HOTREMOVE)
- - Page Migration (CONFIG_MIGRATION)
+ - Allow for memory hot remove (``CONFIG_MEMORY_HOTREMOVE``)
+ - Page Migration (``CONFIG_MIGRATION``)
- For ACPI memory hotplug, the following are also necessary:
- - Memory hotplug (under ACPI Support menu) (CONFIG_ACPI_HOTPLUG_MEMORY)
+ - Memory hotplug (under ACPI Support menu) (``CONFIG_ACPI_HOTPLUG_MEMORY``)
- This option can be kernel module.
- As a related configuration, if your box has a feature of NUMA-node hotplug
via ACPI, then this option is necessary too.
- ACPI0004,PNP0A05 and PNP0A06 Container Driver (under ACPI Support menu)
- (CONFIG_ACPI_CONTAINER).
+ (``CONFIG_ACPI_CONTAINER``).
This option can be kernel module too.
==============================
All memory blocks have their device information in sysfs. Each memory block
-is described under /sys/devices/system/memory as:
+is described under ``/sys/devices/system/memory`` as::
/sys/devices/system/memory/memoryXXX
- (XXX is the memory block id.)
+
+where XXX is the memory block id.
For the memory block covered by the sysfs directory. It is expected that all
memory sections in this range are present and no memory holes exist in the
block.
For example, assume 1GiB memory block size. A device for a memory starting at
-0x100000000 is /sys/device/system/memory/memory4::
+0x100000000 is ``/sys/device/system/memory/memory4``::
(0x100000000 / 1Gib = 4)
Under each memory block, you can see 5 files:
-- /sys/devices/system/memory/memoryXXX/phys_index
-- /sys/devices/system/memory/memoryXXX/phys_device
-- /sys/devices/system/memory/memoryXXX/state
-- /sys/devices/system/memory/memoryXXX/removable
-- /sys/devices/system/memory/memoryXXX/valid_zones
+- ``/sys/devices/system/memory/memoryXXX/phys_index``
+- ``/sys/devices/system/memory/memoryXXX/phys_device``
+- ``/sys/devices/system/memory/memoryXXX/state``
+- ``/sys/devices/system/memory/memoryXXX/removable``
+- ``/sys/devices/system/memory/memoryXXX/valid_zones``
=================== ============================================================
``phys_index`` read-only and contains memory block id, same as XXX.
These directories/files appear after physical memory hotplug phase.
If CONFIG_NUMA is enabled the memoryXXX/ directories can also be accessed
-via symbolic links located in the /sys/devices/system/node/node* directories.
+via symbolic links located in the ``/sys/devices/system/node/node*`` directories.
+
+For example::
-For example:
-/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
+ /sys/devices/system/node/node0/memory9 -> ../../memory/memory9
-A backlink will also be created:
-/sys/devices/system/memory/memory9/node0 -> ../../node/node0
+A backlink will also be created::
+
+ /sys/devices/system/memory/memory9/node0 -> ../../node/node0
.. _memory_hotplug_physical_mem:
calls hotplug code for all of objects which are defined in it.
If memory device is found, memory hotplug code will be called.
-
Notify memory hot-add event by hand
-----------------------------------
if hotplug is supported, although for x86 this should be handled by ACPI
notification.
-Probe interface is located at
-/sys/devices/system/memory/probe
+Probe interface is located at::
+
+ /sys/devices/system/memory/probe
You can tell the physical address of new memory to the kernel by::
not called (in current implementation). You'll have to online memory by
yourself. Please see :ref:`memory_hotplug_how_to_online_memory`.
-
Logical Memory hot-add phase
============================
be hotplugged. Currently offline blocks keep their state. It is possible, under
certain circumstances, that some memory blocks will be added but will fail to
online. User space tools can check their "state" files
-(/sys/devices/system/memory/memoryXXX/state) and try to online them manually.
+(``/sys/devices/system/memory/memoryXXX/state``) and try to online them manually.
If the automatic onlining wasn't requested, failed, or some memory block was
offlined it is possible to change the individual block's state by writing to the
This may be changed in future.
-
-
Logical memory remove
=====================
Hotplugging events are sent to a notification queue.
-There are six types of notification defined in include/linux/memory.h:
+There are six types of notification defined in ``include/linux/memory.h``:
MEM_GOING_ONLINE
Generated before new memory becomes available in order to be able to
The callback routine shall return one of the values
NOTIFY_DONE, NOTIFY_OK, NOTIFY_BAD, NOTIFY_STOP
-defined in include/linux/notifier.h
+defined in ``include/linux/notifier.h``
NOTIFY_DONE and NOTIFY_OK have no effect on the further processing.