aboutsummaryrefslogtreecommitdiff
path: root/Documentation/admin-guide
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/LSM/Yama.rst4
-rw-r--r--Documentation/admin-guide/README.rst3
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt2
-rw-r--r--Documentation/admin-guide/l1tf.rst2
-rw-r--r--Documentation/admin-guide/mm/index.rst1
-rw-r--r--Documentation/admin-guide/mm/memory-hotplug.rst404
6 files changed, 410 insertions, 6 deletions
diff --git a/Documentation/admin-guide/LSM/Yama.rst b/Documentation/admin-guide/LSM/Yama.rst
index 13468ea696b7..d0a060de3973 100644
--- a/Documentation/admin-guide/LSM/Yama.rst
+++ b/Documentation/admin-guide/LSM/Yama.rst
@@ -64,8 +64,8 @@ The sysctl settings (writable only with ``CAP_SYS_PTRACE``) are:
Using ``PTRACE_TRACEME`` is unchanged.
2 - admin-only attach:
- only processes with ``CAP_SYS_PTRACE`` may use ptrace
- with ``PTRACE_ATTACH``, or through children calling ``PTRACE_TRACEME``.
+ only processes with ``CAP_SYS_PTRACE`` may use ptrace, either with
+ ``PTRACE_ATTACH`` or through children calling ``PTRACE_TRACEME``.
3 - no attach:
no processes may use ptrace with ``PTRACE_ATTACH`` nor via
diff --git a/Documentation/admin-guide/README.rst b/Documentation/admin-guide/README.rst
index 15ea785b2dfa..0797eec76be1 100644
--- a/Documentation/admin-guide/README.rst
+++ b/Documentation/admin-guide/README.rst
@@ -51,8 +51,7 @@ Documentation
- There are various README files in the Documentation/ subdirectory:
these typically contain kernel-specific installation notes for some
- drivers for example. See Documentation/00-INDEX for a list of what
- is contained in each file. Please read the
+ drivers for example. Please read the
:ref:`Documentation/process/changes.rst <changes>` file, as it
contains information about the problems, which may result by upgrading
your kernel.
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 4cdcd1a1bbc3..e129cd8a6dcc 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1764,7 +1764,7 @@
Format: { "0" | "1" }
0 - Use IOMMU translation for DMA.
1 - Bypass the IOMMU for DMA.
- unset - Use IOMMU translation for DMA.
+ unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
io7= [HW] IO7 for Marvel based alpha systems
See comment before marvel_specify_io7 in
diff --git a/Documentation/admin-guide/l1tf.rst b/Documentation/admin-guide/l1tf.rst
index bae52b845de0..b85dd80510b0 100644
--- a/Documentation/admin-guide/l1tf.rst
+++ b/Documentation/admin-guide/l1tf.rst
@@ -553,7 +553,7 @@ When nested virtualization is in use, three operating systems are involved:
the bare metal hypervisor, the nested hypervisor and the nested virtual
machine. VMENTER operations from the nested hypervisor into the nested
guest will always be processed by the bare metal hypervisor. If KVM is the
-bare metal hypervisor it wiil:
+bare metal hypervisor it will:
- Flush the L1D cache on every switch from the nested hypervisor to the
nested virtual machine, so that the nested hypervisor's secrets are not
diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst
index ceead68c2df7..8edb35f11317 100644
--- a/Documentation/admin-guide/mm/index.rst
+++ b/Documentation/admin-guide/mm/index.rst
@@ -29,6 +29,7 @@ the Linux memory management.
hugetlbpage
idle_page_tracking
ksm
+ memory-hotplug
numa_memory_policy
pagemap
soft-dirty
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
new file mode 100644
index 000000000000..25157aec5b31
--- /dev/null
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -0,0 +1,404 @@
+.. _admin_guide_memory_hotplug:
+
+==============
+Memory Hotplug
+==============
+
+:Created: Jul 28 2007
+:Updated: Add description of notifier of memory hotplug: Oct 11 2007
+
+This document is about memory hotplug including how-to-use and current status.
+Because Memory Hotplug is still under development, contents of this text will
+be changed often.
+
+.. contents:: :local:
+
+.. note::
+
+ (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``.
+
+
+Introduction
+============
+
+Purpose of memory hotplug
+-------------------------
+
+Memory Hotplug allows users to increase/decrease the amount of memory.
+Generally, there are two purposes.
+
+(A) For changing the amount of memory.
+ This is to allow a feature like capacity on demand.
+(B) For installing/removing DIMMs or NUMA-nodes physically.
+ This is to exchange DIMMs/NUMA-nodes, reduce power consumption, etc.
+
+(A) is required by highly virtualized environments and (B) is required by
+hardware which supports memory power management.
+
+Linux memory hotplug is designed for both purpose.
+
+Phases of memory hotplug
+------------------------
+
+There are 2 phases in Memory Hotplug:
+
+ 1) Physical Memory Hotplug phase
+ 2) Logical Memory Hotplug phase.
+
+The First phase is to communicate hardware/firmware and make/erase
+environment for hotplugged memory. Basically, this phase is necessary
+for the purpose (B), but this is good phase for communication between
+highly virtualized environments too.
+
+When memory is hotplugged, the kernel recognizes new memory, makes new memory
+management tables, and makes sysfs files for new memory's operation.
+
+If firmware supports notification of connection of new memory to OS,
+this phase is triggered automatically. ACPI can notify this event. If not,
+"probe" operation by system administration is used instead.
+(see :ref:`memory_hotplug_physical_mem`).
+
+Logical Memory Hotplug phase is to change memory state into
+available/unavailable for users. Amount of memory from user's view is
+changed by this phase. The kernel makes all memory in it as free pages
+when a memory range is available.
+
+In this document, this phase is described as online/offline.
+
+Logical Memory Hotplug phase is triggered by write of sysfs file by system
+administrator. For the hot-add case, it must be executed after Physical Hotplug
+phase by hand.
+(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
+---------------------------------------
+
+Memory hotplug uses SPARSEMEM memory model which allows memory to be divided
+into chunks of the same size. These chunks are called "sections". The size of
+a memory section is architecture dependent. For example, power uses 16MiB, ia64
+uses 1GiB.
+
+Memory sections are combined into chunks referred to as "memory blocks". The
+size of a memory block is architecture dependent and represents the logical
+unit upon which memory online/offline operations are to be performed. The
+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
+
+Kernel Configuration
+====================
+
+To use memory hotplug feature, kernel must be compiled with following
+config options.
+
+- For all 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``)
+
+- For ACPI memory hotplug, the following are also necessary:
+ - 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``).
+
+ This option can be kernel module too.
+
+
+.. _memory_hotplug_sysfs_files:
+
+sysfs files for memory hotplug
+==============================
+
+All memory blocks have their device information in sysfs. Each memory block
+is described under ``/sys/devices/system/memory`` as::
+
+ /sys/devices/system/memory/memoryXXX
+
+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
+range. Currently there is no way to determine if there is a memory hole, but
+the existence of one should not affect the hotplug capabilities of the memory
+block.
+
+For example, assume 1GiB memory block size. A device for a memory starting at
+0x100000000 is ``/sys/device/system/memory/memory4``::
+
+ (0x100000000 / 1Gib = 4)
+
+This device covers address range [0x100000000 ... 0x140000000)
+
+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``
+
+=================== ============================================================
+``phys_index`` read-only and contains memory block id, same as XXX.
+``state`` read-write
+
+ - at read: contains online/offline state of memory.
+ - at write: user can specify "online_kernel",
+
+ "online_movable", "online", "offline" command
+ which will be performed on all sections in the block.
+``phys_device`` read-only: designed to show the name of physical memory
+ device. This is not well implemented now.
+``removable`` read-only: contains an integer value indicating
+ whether the memory block is removable or not
+ removable. A value of 1 indicates that the memory
+ block is removable and a value of 0 indicates that
+ it is not removable. A memory block is removable only if
+ every section in the block is removable.
+``valid_zones`` read-only: designed to show which zones this memory block
+ can be onlined to.
+
+ The first column shows it`s default zone.
+
+ "memory6/valid_zones: Normal Movable" shows this memoryblock
+ can be onlined to ZONE_NORMAL by default and to ZONE_MOVABLE
+ by online_movable.
+
+ "memory7/valid_zones: Movable Normal" shows this memoryblock
+ can be onlined to ZONE_MOVABLE by default and to ZONE_NORMAL
+ by online_kernel.
+=================== ============================================================
+
+.. note::
+
+ 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.
+
+For example::
+
+ /sys/devices/system/node/node0/memory9 -> ../../memory/memory9
+
+A backlink will also be created::
+
+ /sys/devices/system/memory/memory9/node0 -> ../../node/node0
+
+.. _memory_hotplug_physical_mem:
+
+Physical memory hot-add phase
+=============================
+
+Hardware(Firmware) Support
+--------------------------
+
+On x86_64/ia64 platform, memory hotplug by ACPI is supported.
+
+In general, the firmware (ACPI) which supports memory hotplug defines
+memory class object of _HID "PNP0C80". When a notify is asserted to PNP0C80,
+Linux's ACPI handler does hot-add memory to the system and calls a hotplug udev
+script. This will be done automatically.
+
+But scripts for memory hotplug are not contained in generic udev package(now).
+You may have to write it by yourself or online/offline memory by hand.
+Please see :ref:`memory_hotplug_how_to_online_memory` and
+:ref:`memory_hotplug_how_to_offline_memory`.
+
+If firmware supports NUMA-node hotplug, and defines an object _HID "ACPI0004",
+"PNP0A05", or "PNP0A06", notification is asserted to it, and ACPI handler
+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
+-----------------------------------
+
+On some architectures, the firmware may not notify the kernel of a memory
+hotplug event. Therefore, the memory "probe" interface is supported to
+explicitly notify the kernel. This interface depends on
+CONFIG_ARCH_MEMORY_PROBE and can be configured on powerpc, sh, and x86
+if hotplug is supported, although for x86 this should be handled by ACPI
+notification.
+
+Probe interface is located at::
+
+ /sys/devices/system/memory/probe
+
+You can tell the physical address of new memory to the kernel by::
+
+ % echo start_address_of_new_memory > /sys/devices/system/memory/probe
+
+Then, [start_address_of_new_memory, start_address_of_new_memory +
+memory_block_size] memory range is hot-added. In this case, hotplug script is
+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
+============================
+
+State of memory
+---------------
+
+To see (online/offline) state of a memory block, read 'state' file::
+
+ % cat /sys/device/system/memory/memoryXXX/state
+
+
+- If the memory block is online, you'll read "online".
+- If the memory block is offline, you'll read "offline".
+
+
+.. _memory_hotplug_how_to_online_memory:
+
+How to online memory
+--------------------
+
+When the memory is hot-added, the kernel decides whether or not to "online"
+it according to the policy which can be read from "auto_online_blocks" file::
+
+ % cat /sys/devices/system/memory/auto_online_blocks
+
+The default depends on the CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
+option. If it is disabled the default is "offline" which means the newly added
+memory is not in a ready-to-use state and you have to "online" the newly added
+memory blocks manually. Automatic onlining can be requested by writing "online"
+to "auto_online_blocks" file::
+
+ % echo online > /sys/devices/system/memory/auto_online_blocks
+
+This sets a global policy and impacts all memory blocks that will subsequently
+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.
+
+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
+"state" file::
+
+ % echo online > /sys/devices/system/memory/memoryXXX/state
+
+This onlining will not change the ZONE type of the target memory block,
+If the memory block doesn't belong to any zone an appropriate kernel zone
+(usually ZONE_NORMAL) will be used unless movable_node kernel command line
+option is specified when ZONE_MOVABLE will be used.
+
+You can explicitly request to associate it with ZONE_MOVABLE by::
+
+ % echo online_movable > /sys/devices/system/memory/memoryXXX/state
+
+.. note:: current limit: this memory block must be adjacent to ZONE_MOVABLE
+
+Or you can explicitly request a kernel zone (usually ZONE_NORMAL) by::
+
+ % echo online_kernel > /sys/devices/system/memory/memoryXXX/state
+
+.. note:: current limit: this memory block must be adjacent to ZONE_NORMAL
+
+An explicit zone onlining can fail (e.g. when the range is already within
+and existing and incompatible zone already).
+
+After this, memory block XXX's state will be 'online' and the amount of
+available memory will be increased.
+
+This may be changed in future.
+
+Logical memory remove
+=====================
+
+Memory offline and ZONE_MOVABLE
+-------------------------------
+
+Memory offlining is more complicated than memory online. Because memory offline
+has to make the whole memory block be unused, memory offline can fail if
+the memory block includes memory which cannot be freed.
+
+In general, memory offline can use 2 techniques.
+
+(1) reclaim and free all memory in the memory block.
+(2) migrate all pages in the memory block.
+
+In the current implementation, Linux's memory offline uses method (2), freeing
+all pages in the memory block by page migration. But not all pages are
+migratable. Under current Linux, migratable pages are anonymous pages and
+page caches. For offlining a memory block by migration, the kernel has to
+guarantee that the memory block contains only migratable pages.
+
+Now, a boot option for making a memory block which consists of migratable pages
+is supported. By specifying "kernelcore=" or "movablecore=" boot option, you can
+create ZONE_MOVABLE...a zone which is just used for movable pages.
+(See also Documentation/admin-guide/kernel-parameters.rst)
+
+Assume the system has "TOTAL" amount of memory at boot time, this boot option
+creates ZONE_MOVABLE as following.
+
+1) When kernelcore=YYYY boot option is used,
+ Size of memory not for movable pages (not for offline) is YYYY.
+ Size of memory for movable pages (for offline) is TOTAL-YYYY.
+
+2) When movablecore=ZZZZ boot option is used,
+ Size of memory not for movable pages (not for offline) is TOTAL - ZZZZ.
+ Size of memory for movable pages (for offline) is ZZZZ.
+
+.. note::
+
+ Unfortunately, there is no information to show which memory block belongs
+ to ZONE_MOVABLE. This is TBD.
+
+.. _memory_hotplug_how_to_offline_memory:
+
+How to offline memory
+---------------------
+
+You can offline a memory block by using the same sysfs interface that was used
+in memory onlining::
+
+ % echo offline > /sys/devices/system/memory/memoryXXX/state
+
+If offline succeeds, the state of the memory block is changed to be "offline".
+If it fails, some error core (like -EBUSY) will be returned by the kernel.
+Even if a memory block does not belong to ZONE_MOVABLE, you can try to offline
+it. If it doesn't contain 'unmovable' memory, you'll get success.
+
+A memory block under ZONE_MOVABLE is considered to be able to be offlined
+easily. But under some busy state, it may return -EBUSY. Even if a memory
+block cannot be offlined due to -EBUSY, you can retry offlining it and may be
+able to offline it (or not). (For example, a page is referred to by some kernel
+internal call and released soon.)
+
+Consideration:
+ Memory hotplug's design direction is to make the possibility of memory
+ offlining higher and to guarantee unplugging memory under any situation. But
+ it needs more work. Returning -EBUSY under some situation may be good because
+ the user can decide to retry more or not by himself. Currently, memory
+ offlining code does some amount of retry with 120 seconds timeout.
+
+Physical memory remove
+======================
+
+Need more implementation yet....
+ - Notification completion of remove works by OS to firmware.
+ - Guard from remove if not yet.
+
+Future Work
+===========
+
+ - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
+ sysctl or new control file.
+ - showing memory block and physical device relationship.
+ - test and make it better memory offlining.
+ - support HugeTLB page migration and offlining.
+ - memmap removing at memory offline.
+ - physical remove memory.