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docs: move memory hotplug description into admin-guide/mm
The memory hotplug description in Documentation/memory-hotplug.txt is already formatted as ReST and can be easily added to admin-guide/mm section. While on it, slightly update formatting to make it consistent with the doc-guide. Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Mike Rapoport
Jonathan Corbet
parent
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6bf53999a3
@ -29,6 +29,7 @@ the Linux memory management.
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hugetlbpage
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idle_page_tracking
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ksm
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memory-hotplug
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numa_memory_policy
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pagemap
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soft-dirty
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@ -1,3 +1,5 @@
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.. _admin_guide_memory_hotplug:
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==============
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Memory Hotplug
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==============
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@ -9,10 +11,12 @@ This document is about memory hotplug including how-to-use and current status.
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Because Memory Hotplug is still under development, contents of this text will
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be changed often.
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.. contents:: :local:
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.. CONTENTS
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1. Introduction
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1.1 purpose of memory hotplug
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1.1 Purpose of memory hotplug
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1.2. Phases of memory hotplug
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1.3. Unit of Memory online/offline operation
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2. Kernel Configuration
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@ -35,13 +39,13 @@ be changed often.
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(1) x86_64's has special implementation for memory hotplug.
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This text does not describe it.
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(2) This text assumes that sysfs is mounted at /sys.
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(2) This text assumes that sysfs is mounted at ``/sys``.
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Introduction
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============
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purpose of memory hotplug
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Purpose of memory hotplug
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-------------------------
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Memory Hotplug allows users to increase/decrease the amount of memory.
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@ -57,7 +61,6 @@ hardware which supports memory power management.
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Linux memory hotplug is designed for both purpose.
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Phases of memory hotplug
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------------------------
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@ -92,7 +95,6 @@ phase by hand.
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(However, if you writes udev's hotplug scripts for memory hotplug, these
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phases can be execute in seamless way.)
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Unit of Memory online/offline operation
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---------------------------------------
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@ -107,10 +109,9 @@ unit upon which memory online/offline operations are to be performed. The
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default size of a memory block is the same as memory section size unless an
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architecture specifies otherwise. (see :ref:`memory_hotplug_sysfs_files`.)
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To determine the size (in bytes) of a memory block please read this file:
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/sys/devices/system/memory/block_size_bytes
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To determine the size (in bytes) of a memory block please read this file::
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/sys/devices/system/memory/block_size_bytes
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Kernel Configuration
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====================
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@ -119,22 +120,22 @@ To use memory hotplug feature, kernel must be compiled with following
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config options.
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- For all memory hotplug:
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- Memory model -> Sparse Memory (CONFIG_SPARSEMEM)
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- Allow for memory hot-add (CONFIG_MEMORY_HOTPLUG)
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- Memory model -> Sparse Memory (``CONFIG_SPARSEMEM``)
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- Allow for memory hot-add (``CONFIG_MEMORY_HOTPLUG``)
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- To enable memory removal, the following are also necessary:
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- Allow for memory hot remove (CONFIG_MEMORY_HOTREMOVE)
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- Page Migration (CONFIG_MIGRATION)
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- Allow for memory hot remove (``CONFIG_MEMORY_HOTREMOVE``)
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- Page Migration (``CONFIG_MIGRATION``)
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- For ACPI memory hotplug, the following are also necessary:
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- Memory hotplug (under ACPI Support menu) (CONFIG_ACPI_HOTPLUG_MEMORY)
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- Memory hotplug (under ACPI Support menu) (``CONFIG_ACPI_HOTPLUG_MEMORY``)
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- This option can be kernel module.
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- As a related configuration, if your box has a feature of NUMA-node hotplug
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via ACPI, then this option is necessary too.
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- ACPI0004,PNP0A05 and PNP0A06 Container Driver (under ACPI Support menu)
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(CONFIG_ACPI_CONTAINER).
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(``CONFIG_ACPI_CONTAINER``).
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This option can be kernel module too.
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@ -145,10 +146,11 @@ sysfs files for memory hotplug
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==============================
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All memory blocks have their device information in sysfs. Each memory block
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is described under /sys/devices/system/memory as:
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is described under ``/sys/devices/system/memory`` as::
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/sys/devices/system/memory/memoryXXX
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(XXX is the memory block id.)
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where XXX is the memory block id.
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For the memory block covered by the sysfs directory. It is expected that all
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memory sections in this range are present and no memory holes exist in the
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@ -157,7 +159,7 @@ the existence of one should not affect the hotplug capabilities of the memory
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block.
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For example, assume 1GiB memory block size. A device for a memory starting at
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0x100000000 is /sys/device/system/memory/memory4::
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0x100000000 is ``/sys/device/system/memory/memory4``::
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(0x100000000 / 1Gib = 4)
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@ -165,11 +167,11 @@ This device covers address range [0x100000000 ... 0x140000000)
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Under each memory block, you can see 5 files:
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- /sys/devices/system/memory/memoryXXX/phys_index
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- /sys/devices/system/memory/memoryXXX/phys_device
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- /sys/devices/system/memory/memoryXXX/state
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- /sys/devices/system/memory/memoryXXX/removable
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- /sys/devices/system/memory/memoryXXX/valid_zones
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- ``/sys/devices/system/memory/memoryXXX/phys_index``
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- ``/sys/devices/system/memory/memoryXXX/phys_device``
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- ``/sys/devices/system/memory/memoryXXX/state``
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- ``/sys/devices/system/memory/memoryXXX/removable``
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- ``/sys/devices/system/memory/memoryXXX/valid_zones``
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=================== ============================================================
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``phys_index`` read-only and contains memory block id, same as XXX.
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@ -207,13 +209,15 @@ Under each memory block, you can see 5 files:
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These directories/files appear after physical memory hotplug phase.
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If CONFIG_NUMA is enabled the memoryXXX/ directories can also be accessed
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via symbolic links located in the /sys/devices/system/node/node* directories.
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via symbolic links located in the ``/sys/devices/system/node/node*`` directories.
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For example:
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/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
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For example::
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A backlink will also be created:
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/sys/devices/system/memory/memory9/node0 -> ../../node/node0
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/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
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A backlink will also be created::
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/sys/devices/system/memory/memory9/node0 -> ../../node/node0
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.. _memory_hotplug_physical_mem:
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@ -240,7 +244,6 @@ If firmware supports NUMA-node hotplug, and defines an object _HID "ACPI0004",
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calls hotplug code for all of objects which are defined in it.
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If memory device is found, memory hotplug code will be called.
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Notify memory hot-add event by hand
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-----------------------------------
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@ -251,8 +254,9 @@ CONFIG_ARCH_MEMORY_PROBE and can be configured on powerpc, sh, and x86
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if hotplug is supported, although for x86 this should be handled by ACPI
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notification.
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Probe interface is located at
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/sys/devices/system/memory/probe
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Probe interface is located at::
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/sys/devices/system/memory/probe
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You can tell the physical address of new memory to the kernel by::
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@ -263,7 +267,6 @@ memory_block_size] memory range is hot-added. In this case, hotplug script is
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not called (in current implementation). You'll have to online memory by
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yourself. Please see :ref:`memory_hotplug_how_to_online_memory`.
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Logical Memory hot-add phase
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============================
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@ -301,7 +304,7 @@ This sets a global policy and impacts all memory blocks that will subsequently
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be hotplugged. Currently offline blocks keep their state. It is possible, under
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certain circumstances, that some memory blocks will be added but will fail to
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online. User space tools can check their "state" files
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(/sys/devices/system/memory/memoryXXX/state) and try to online them manually.
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(``/sys/devices/system/memory/memoryXXX/state``) and try to online them manually.
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If the automatic onlining wasn't requested, failed, or some memory block was
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offlined it is possible to change the individual block's state by writing to the
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@ -334,8 +337,6 @@ available memory will be increased.
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This may be changed in future.
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Logical memory remove
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=====================
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@ -418,7 +419,7 @@ Memory hotplug event notifier
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Hotplugging events are sent to a notification queue.
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There are six types of notification defined in include/linux/memory.h:
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There are six types of notification defined in ``include/linux/memory.h``:
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MEM_GOING_ONLINE
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Generated before new memory becomes available in order to be able to
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@ -485,7 +486,7 @@ The third argument (arg) passes a pointer of struct memory_notify::
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The callback routine shall return one of the values
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NOTIFY_DONE, NOTIFY_OK, NOTIFY_BAD, NOTIFY_STOP
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defined in include/linux/notifier.h
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defined in ``include/linux/notifier.h``
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NOTIFY_DONE and NOTIFY_OK have no effect on the further processing.
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