mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-06 04:14:13 +08:00
d9713679db
Currently memory_hotplug only manages the node_states[N_HIGH_MEMORY], it forgets to manage node_states[N_NORMAL_MEMORY]. This may cause node_states[N_NORMAL_MEMORY] to become incorrect. Example, if a node is empty before online, and we online a memory which is in ZONE_NORMAL. And after online, node_states[N_HIGH_MEMORY] is correct, but node_states[N_NORMAL_MEMORY] is incorrect, the online code doesn't set the new online node to node_states[N_NORMAL_MEMORY]. The same thing will happen when offlining (the offline code doesn't clear the node from node_states[N_NORMAL_MEMORY] when needed). Some memory managment code depends node_states[N_NORMAL_MEMORY], so we have to fix up the node_states[N_NORMAL_MEMORY]. We add node_states_check_changes_online() and node_states_check_changes_offline() to detect whether node_states[N_HIGH_MEMORY] and node_states[N_NORMAL_MEMORY] are changed while hotpluging. Also add @status_change_nid_normal to struct memory_notify, thus the memory hotplug callbacks know whether the node_states[N_NORMAL_MEMORY] are changed. (We can add a @flags and reuse @status_change_nid instead of introducing @status_change_nid_normal, but it will add much more complexity in memory hotplug callback in every subsystem. So introducing @status_change_nid_normal is better and it doesn't change the sematics of @status_change_nid) Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: David Rientjes <rientjes@google.com> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Cc: Rob Landley <rob@landley.net> Cc: Jiang Liu <jiang.liu@huawei.com> Cc: Kay Sievers <kay.sievers@vrfy.org> Cc: Greg Kroah-Hartman <gregkh@suse.de> Cc: Mel Gorman <mgorman@suse.de> Cc: Wen Congyang <wency@cn.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
406 lines
15 KiB
Plaintext
406 lines
15 KiB
Plaintext
==============
|
|
Memory Hotplug
|
|
==============
|
|
|
|
Created: Jul 28 2007
|
|
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.
|
|
|
|
1. Introduction
|
|
1.1 purpose of memory hotplug
|
|
1.2. Phases of memory hotplug
|
|
1.3. Unit of Memory online/offline operation
|
|
2. Kernel Configuration
|
|
3. sysfs files for memory hotplug
|
|
4. Physical memory hot-add phase
|
|
4.1 Hardware(Firmware) Support
|
|
4.2 Notify memory hot-add event by hand
|
|
5. Logical Memory hot-add phase
|
|
5.1. State of memory
|
|
5.2. How to online memory
|
|
6. Logical memory remove
|
|
6.1 Memory offline and ZONE_MOVABLE
|
|
6.2. How to offline memory
|
|
7. Physical memory remove
|
|
8. Memory hotplug event notifier
|
|
9. Future Work List
|
|
|
|
Note(1): x86_64's has special implementation for memory hotplug.
|
|
This text does not describe it.
|
|
Note(2): This text assumes that sysfs is mounted at /sys.
|
|
|
|
|
|
---------------
|
|
1. Introduction
|
|
---------------
|
|
|
|
1.1 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.
|
|
|
|
|
|
1.2. 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 Section 4.).
|
|
|
|
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.)
|
|
|
|
|
|
1.3. Unit of Memory online/offline operation
|
|
------------
|
|
Memory hotplug uses SPARSEMEM memory model. SPARSEMEM divides the whole memory
|
|
into chunks of the same size. The chunk is called a "section". The size of
|
|
a section is architecture dependent. For example, power uses 16MiB, ia64 uses
|
|
1GiB. The unit of online/offline operation is "one section". (see Section 3.)
|
|
|
|
To determine the size of sections, please read this file:
|
|
|
|
/sys/devices/system/memory/block_size_bytes
|
|
|
|
This file shows the size of sections in byte.
|
|
|
|
-----------------------
|
|
2. 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 followings are also necessary
|
|
Allow for memory hot remove (CONFIG_MEMORY_HOTREMOVE)
|
|
Page Migration (CONFIG_MIGRATION)
|
|
|
|
- For ACPI memory hotplug, the followings 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.
|
|
|
|
--------------------------------
|
|
4 sysfs files for memory hotplug
|
|
--------------------------------
|
|
All sections have their device information in sysfs. Each section is part of
|
|
a memory block under /sys/devices/system/memory as
|
|
|
|
/sys/devices/system/memory/memoryXXX
|
|
(XXX is the section id.)
|
|
|
|
Now, XXX is defined as (start_address_of_section / section_size) of the first
|
|
section contained in the memory block. The files 'phys_index' and
|
|
'end_phys_index' under each directory report the beginning and end section id's
|
|
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 section 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 section, you can see 4 or 5 files, the end_phys_index file being
|
|
a recent addition and not present on older kernels.
|
|
|
|
/sys/devices/system/memory/memoryXXX/start_phys_index
|
|
/sys/devices/system/memory/memoryXXX/end_phys_index
|
|
/sys/devices/system/memory/memoryXXX/phys_device
|
|
/sys/devices/system/memory/memoryXXX/state
|
|
/sys/devices/system/memory/memoryXXX/removable
|
|
|
|
'phys_index' : read-only and contains section id of the first section
|
|
in the memory block, same as XXX.
|
|
'end_phys_index' : read-only and contains section id of the last section
|
|
in the memory block.
|
|
'state' : read-write
|
|
at read: contains online/offline state of memory.
|
|
at write: user can specify "online", "offline" command
|
|
which will be performed on al 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.
|
|
|
|
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
|
|
|
|
--------------------------------
|
|
4. Physical memory hot-add phase
|
|
--------------------------------
|
|
|
|
4.1 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 "How to online memory", "How to offline memory" in this text.
|
|
|
|
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.
|
|
|
|
|
|
4.2 Notify memory hot-add event by hand
|
|
------------
|
|
In some environments, especially virtualized environment, firmware will not
|
|
notify memory hotplug event to the kernel. For such environment, "probe"
|
|
interface is supported. This interface depends on CONFIG_ARCH_MEMORY_PROBE.
|
|
|
|
Now, CONFIG_ARCH_MEMORY_PROBE is supported only by powerpc but it does not
|
|
contain highly architecture codes. Please add config if you need "probe"
|
|
interface.
|
|
|
|
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 + section_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 "How to online memory" in this text.
|
|
|
|
|
|
|
|
------------------------------
|
|
5. Logical Memory hot-add phase
|
|
------------------------------
|
|
|
|
5.1. State of memory
|
|
------------
|
|
To see (online/offline) state of memory section, read 'state' file.
|
|
|
|
% cat /sys/device/system/memory/memoryXXX/state
|
|
|
|
|
|
If the memory section is online, you'll read "online".
|
|
If the memory section is offline, you'll read "offline".
|
|
|
|
|
|
5.2. How to online memory
|
|
------------
|
|
Even if the memory is hot-added, it is not at ready-to-use state.
|
|
For using newly added memory, you have to "online" the memory section.
|
|
|
|
For onlining, you have to write "online" to the section's state file as:
|
|
|
|
% echo online > /sys/devices/system/memory/memoryXXX/state
|
|
|
|
After this, section memoryXXX's state will be 'online' and the amount of
|
|
available memory will be increased.
|
|
|
|
Currently, newly added memory is added as ZONE_NORMAL (for powerpc, ZONE_DMA).
|
|
This may be changed in future.
|
|
|
|
|
|
|
|
------------------------
|
|
6. Logical memory remove
|
|
------------------------
|
|
|
|
6.1 Memory offline and ZONE_MOVABLE
|
|
------------
|
|
Memory offlining is more complicated than memory online. Because memory offline
|
|
has to make the whole memory section be unused, memory offline can fail if
|
|
the section includes memory which cannot be freed.
|
|
|
|
In general, memory offline can use 2 techniques.
|
|
|
|
(1) reclaim and free all memory in the section.
|
|
(2) migrate all pages in the section.
|
|
|
|
In the current implementation, Linux's memory offline uses method (2), freeing
|
|
all pages in the section by page migration. But not all pages are
|
|
migratable. Under current Linux, migratable pages are anonymous pages and
|
|
page caches. For offlining a section by migration, the kernel has to guarantee
|
|
that the section contains only migratable pages.
|
|
|
|
Now, a boot option for making a section 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/kernel-parameters.txt)
|
|
|
|
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 section belongs
|
|
to ZONE_MOVABLE. This is TBD.
|
|
|
|
|
|
6.2. How to offline memory
|
|
------------
|
|
You can offline a section 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 section is changed to be "offline".
|
|
If it fails, some error core (like -EBUSY) will be returned by the kernel.
|
|
Even if a section does not belong to ZONE_MOVABLE, you can try to offline it.
|
|
If it doesn't contain 'unmovable' memory, you'll get success.
|
|
|
|
A section 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 section
|
|
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.
|
|
|
|
-------------------------
|
|
7. Physical memory remove
|
|
-------------------------
|
|
Need more implementation yet....
|
|
- Notification completion of remove works by OS to firmware.
|
|
- Guard from remove if not yet.
|
|
|
|
--------------------------------
|
|
8. Memory hotplug event notifier
|
|
--------------------------------
|
|
Memory hotplug has event notifier. There are 6 types of notification.
|
|
|
|
MEMORY_GOING_ONLINE
|
|
Generated before new memory becomes available in order to be able to
|
|
prepare subsystems to handle memory. The page allocator is still unable
|
|
to allocate from the new memory.
|
|
|
|
MEMORY_CANCEL_ONLINE
|
|
Generated if MEMORY_GOING_ONLINE fails.
|
|
|
|
MEMORY_ONLINE
|
|
Generated when memory has successfully brought online. The callback may
|
|
allocate pages from the new memory.
|
|
|
|
MEMORY_GOING_OFFLINE
|
|
Generated to begin the process of offlining memory. Allocations are no
|
|
longer possible from the memory but some of the memory to be offlined
|
|
is still in use. The callback can be used to free memory known to a
|
|
subsystem from the indicated memory section.
|
|
|
|
MEMORY_CANCEL_OFFLINE
|
|
Generated if MEMORY_GOING_OFFLINE fails. Memory is available again from
|
|
the section that we attempted to offline.
|
|
|
|
MEMORY_OFFLINE
|
|
Generated after offlining memory is complete.
|
|
|
|
A callback routine can be registered by
|
|
hotplug_memory_notifier(callback_func, priority)
|
|
|
|
The second argument of callback function (action) is event types of above.
|
|
The third argument is passed by pointer of struct memory_notify.
|
|
|
|
struct memory_notify {
|
|
unsigned long start_pfn;
|
|
unsigned long nr_pages;
|
|
int status_change_nid_normal;
|
|
int status_change_nid;
|
|
}
|
|
|
|
start_pfn is start_pfn of online/offline memory.
|
|
nr_pages is # of pages of online/offline memory.
|
|
status_change_nid_normal is set node id when N_NORMAL_MEMORY of nodemask
|
|
is (will be) set/clear, if this is -1, then nodemask status is not changed.
|
|
status_change_nid is set node id when N_HIGH_MEMORY of nodemask is (will be)
|
|
set/clear. It means a new(memoryless) node gets new memory by online and a
|
|
node loses all memory. If this is -1, then nodemask status is not changed.
|
|
If status_changed_nid* >= 0, callback should create/discard structures for the
|
|
node if necessary.
|
|
|
|
--------------
|
|
9. Future Work
|
|
--------------
|
|
- allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
|
|
sysctl or new control file.
|
|
- showing memory section and physical device relationship.
|
|
- showing memory section is under ZONE_MOVABLE or not
|
|
- test and make it better memory offlining.
|
|
- support HugeTLB page migration and offlining.
|
|
- memmap removing at memory offline.
|
|
- physical remove memory.
|
|
|