Lines Matching +full:memory +full:- +full:to +full:- +full:memory
2 Memory Hotplug
6 :Updated: Add description of notifier of memory hotplug: Oct 11 2007
8 This document is about memory hotplug including how-to-use and current status.
9 Because Memory Hotplug is still under development, contents of this text will
15 1.1 purpose of memory hotplug
16 1.2. Phases of memory hotplug
17 1.3. Unit of Memory online/offline operation
19 3. sysfs files for memory hotplug
20 4. Physical memory hot-add phase
22 4.2 Notify memory hot-add event by hand
23 5. Logical Memory hot-add phase
24 5.1. State of memory
25 5.2. How to online memory
26 6. Logical memory remove
27 6.1 Memory offline and ZONE_MOVABLE
28 6.2. How to offline memory
29 7. Physical memory remove
30 8. Memory hotplug event notifier
36 (1) x86_64's has special implementation for memory hotplug.
44 purpose of memory hotplug
45 -------------------------
47 Memory Hotplug allows users to increase/decrease the amount of memory.
50 (A) For changing the amount of memory.
51 This is to allow a feature like capacity on demand.
52 (B) For installing/removing DIMMs or NUMA-nodes physically.
53 This is to exchange DIMMs/NUMA-nodes, reduce power consumption, etc.
56 hardware which supports memory power management.
58 Linux memory hotplug is designed for both purpose.
61 Phases of memory hotplug
62 ------------------------
64 There are 2 phases in Memory Hotplug:
66 1) Physical Memory Hotplug phase
67 2) Logical Memory Hotplug phase.
69 The First phase is to communicate hardware/firmware and make/erase
70 environment for hotplugged memory. Basically, this phase is necessary
74 When memory is hotplugged, the kernel recognizes new memory, makes new memory
75 management tables, and makes sysfs files for new memory's operation.
77 If firmware supports notification of connection of new memory to OS,
82 Logical Memory Hotplug phase is to change memory state into
83 available/unavailable for users. Amount of memory from user's view is
84 changed by this phase. The kernel makes all memory in it as free pages
85 when a memory range is available.
89 Logical Memory Hotplug phase is triggered by write of sysfs file by system
90 administrator. For the hot-add case, it must be executed after Physical Hotplug
92 (However, if you writes udev's hotplug scripts for memory hotplug, these
96 Unit of Memory online/offline operation
97 ---------------------------------------
99 Memory hotplug uses SPARSEMEM memory model which allows memory to be divided
101 a memory section is architecture dependent. For example, power uses 16MiB, ia64
104 Memory sections are combined into chunks referred to as "memory blocks". The
105 size of a memory block is architecture dependent and represents the logical
106 unit upon which memory online/offline operations are to be performed. The
107 default size of a memory block is the same as memory section size unless an
110 To determine the size (in bytes) of a memory block please read this file:
112 /sys/devices/system/memory/block_size_bytes
118 To use memory hotplug feature, kernel must be compiled with following
121 - For all memory hotplug:
122 - Memory model -> Sparse Memory (CONFIG_SPARSEMEM)
123 - Allow for memory hot-add (CONFIG_MEMORY_HOTPLUG)
125 - To enable memory removal, the following are also necessary:
126 - Allow for memory hot remove (CONFIG_MEMORY_HOTREMOVE)
127 - Page Migration (CONFIG_MIGRATION)
129 - For ACPI memory hotplug, the following are also necessary:
130 - Memory hotplug (under ACPI Support menu) (CONFIG_ACPI_HOTPLUG_MEMORY)
131 - This option can be kernel module.
133 - As a related configuration, if your box has a feature of NUMA-node hotplug
136 - ACPI0004,PNP0A05 and PNP0A06 Container Driver (under ACPI Support menu)
144 sysfs files for memory hotplug
147 All memory blocks have their device information in sysfs. Each memory block
148 is described under /sys/devices/system/memory as:
150 /sys/devices/system/memory/memoryXXX
151 (XXX is the memory block id.)
153 For the memory block covered by the sysfs directory. It is expected that all
154 memory sections in this range are present and no memory holes exist in the
155 range. Currently there is no way to determine if there is a memory hole, but
156 the existence of one should not affect the hotplug capabilities of the memory
159 For example, assume 1GiB memory block size. A device for a memory starting at
160 0x100000000 is /sys/device/system/memory/memory4::
166 Under each memory block, you can see 5 files:
168 - /sys/devices/system/memory/memoryXXX/phys_index
169 - /sys/devices/system/memory/memoryXXX/phys_device
170 - /sys/devices/system/memory/memoryXXX/state
171 - /sys/devices/system/memory/memoryXXX/removable
172 - /sys/devices/system/memory/memoryXXX/valid_zones
175 ``phys_index`` read-only and contains memory block id, same as XXX.
176 ``state`` read-write
178 - at read: contains online/offline state of memory.
179 - at write: user can specify "online_kernel",
183 ``phys_device`` read-only: designed to show the name of physical memory
185 ``removable`` read-only: contains an integer value indicating
186 whether the memory block is removable or not
187 removable. A value of 1 indicates that the memory
189 it is not removable. A memory block is removable only if
191 ``valid_zones`` read-only: designed to show which zones this memory block
192 can be onlined to.
197 can be onlined to ZONE_NORMAL by default and to ZONE_MOVABLE
201 can be onlined to ZONE_MOVABLE by default and to ZONE_NORMAL
207 These directories/files appear after physical memory hotplug phase.
213 /sys/devices/system/node/node0/memory9 -> ../../memory/memory9
216 /sys/devices/system/memory/memory9/node0 -> ../../node/node0
220 Physical memory hot-add phase
224 --------------------------
226 On x86_64/ia64 platform, memory hotplug by ACPI is supported.
228 In general, the firmware (ACPI) which supports memory hotplug defines
229 memory class object of _HID "PNP0C80". When a notify is asserted to PNP0C80,
230 Linux's ACPI handler does hot-add memory to the system and calls a hotplug udev
233 But scripts for memory hotplug are not contained in generic udev package(now).
234 You may have to write it by yourself or online/offline memory by hand.
238 If firmware supports NUMA-node hotplug, and defines an object _HID "ACPI0004",
239 "PNP0A05", or "PNP0A06", notification is asserted to it, and ACPI handler
241 If memory device is found, memory hotplug code will be called.
244 Notify memory hot-add event by hand
245 -----------------------------------
247 On some architectures, the firmware may not notify the kernel of a memory
248 hotplug event. Therefore, the memory "probe" interface is supported to
255 /sys/devices/system/memory/probe
257 You can tell the physical address of new memory to the kernel by::
259 % echo start_address_of_new_memory > /sys/devices/system/memory/probe
262 memory_block_size] memory range is hot-added. In this case, hotplug script is
263 not called (in current implementation). You'll have to online memory by
267 Logical Memory hot-add phase
270 State of memory
271 ---------------
273 To see (online/offline) state of a memory block, read 'state' file::
275 % cat /sys/device/system/memory/memoryXXX/state
278 - If the memory block is online, you'll read "online".
279 - If the memory block is offline, you'll read "offline".
284 How to online memory
285 --------------------
287 When the memory is hot-added, the kernel decides whether or not to "online"
288 it according to the policy which can be read from "auto_online_blocks" file::
290 % cat /sys/devices/system/memory/auto_online_blocks
294 memory is not in a ready-to-use state and you have to "online" the newly added
295 memory blocks manually. Automatic onlining can be requested by writing "online"
296 to "auto_online_blocks" file::
298 % echo online > /sys/devices/system/memory/auto_online_blocks
300 This sets a global policy and impacts all memory blocks that will subsequently
302 certain circumstances, that some memory blocks will be added but will fail to
304 (/sys/devices/system/memory/memoryXXX/state) and try to online them manually.
306 If the automatic onlining wasn't requested, failed, or some memory block was
307 offlined it is possible to change the individual block's state by writing to the
310 % echo online > /sys/devices/system/memory/memoryXXX/state
312 This onlining will not change the ZONE type of the target memory block,
313 If the memory block doesn't belong to any zone an appropriate kernel zone
317 You can explicitly request to associate it with ZONE_MOVABLE by::
319 % echo online_movable > /sys/devices/system/memory/memoryXXX/state
321 .. note:: current limit: this memory block must be adjacent to ZONE_MOVABLE
325 % echo online_kernel > /sys/devices/system/memory/memoryXXX/state
327 .. note:: current limit: this memory block must be adjacent to ZONE_NORMAL
332 After this, memory block XXX's state will be 'online' and the amount of
333 available memory will be increased.
339 Logical memory remove
342 Memory offline and ZONE_MOVABLE
343 -------------------------------
345 Memory offlining is more complicated than memory online. Because memory offline
346 has to make the whole memory block be unused, memory offline can fail if
347 the memory block includes memory which cannot be freed.
349 In general, memory offline can use 2 techniques.
351 (1) reclaim and free all memory in the memory block.
352 (2) migrate all pages in the memory block.
354 In the current implementation, Linux's memory offline uses method (2), freeing
355 all pages in the memory block by page migration. But not all pages are
357 page caches. For offlining a memory block by migration, the kernel has to
358 guarantee that the memory block contains only migratable pages.
360 Now, a boot option for making a memory block which consists of migratable pages
363 (See also Documentation/admin-guide/kernel-parameters.rst)
365 Assume the system has "TOTAL" amount of memory at boot time, this boot option
369 Size of memory not for movable pages (not for offline) is YYYY.
370 Size of memory for movable pages (for offline) is TOTAL-YYYY.
373 Size of memory not for movable pages (not for offline) is TOTAL - ZZZZ.
374 Size of memory for movable pages (for offline) is ZZZZ.
378 Unfortunately, there is no information to show which memory block belongs
379 to ZONE_MOVABLE. This is TBD.
383 How to offline memory
384 ---------------------
386 You can offline a memory block by using the same sysfs interface that was used
387 in memory onlining::
389 % echo offline > /sys/devices/system/memory/memoryXXX/state
391 If offline succeeds, the state of the memory block is changed to be "offline".
392 If it fails, some error core (like -EBUSY) will be returned by the kernel.
393 Even if a memory block does not belong to ZONE_MOVABLE, you can try to offline
394 it. If it doesn't contain 'unmovable' memory, you'll get success.
396 A memory block under ZONE_MOVABLE is considered to be able to be offlined
397 easily. But under some busy state, it may return -EBUSY. Even if a memory
398 block cannot be offlined due to -EBUSY, you can retry offlining it and may be
399 able to offline it (or not). (For example, a page is referred to by some kernel
403 Memory hotplug's design direction is to make the possibility of memory
404 offlining higher and to guarantee unplugging memory under any situation. But
405 it needs more work. Returning -EBUSY under some situation may be good because
406 the user can decide to retry more or not by himself. Currently, memory
409 Physical memory remove
413 - Notification completion of remove works by OS to firmware.
414 - Guard from remove if not yet.
416 Memory hotplug event notifier
419 Hotplugging events are sent to a notification queue.
421 There are six types of notification defined in include/linux/memory.h:
424 Generated before new memory becomes available in order to be able to
425 prepare subsystems to handle memory. The page allocator is still unable
426 to allocate from the new memory.
432 Generated when memory has successfully brought online. The callback may
433 allocate pages from the new memory.
436 Generated to begin the process of offlining memory. Allocations are no
437 longer possible from the memory but some of the memory to be offlined
438 is still in use. The callback can be used to free memory known to a
439 subsystem from the indicated memory block.
442 Generated if MEMORY_GOING_OFFLINE fails. Memory is available again from
443 the memory block that we attempted to offline.
446 Generated after offlining memory is complete.
460 The first argument of the callback function (self) is a pointer to the block
461 of the notifier chain that points to the callback function itself.
473 - start_pfn is start_pfn of online/offline memory.
474 - nr_pages is # of pages of online/offline memory.
475 - status_change_nid_normal is set node id when N_NORMAL_MEMORY of nodemask
476 is (will be) set/clear, if this is -1, then nodemask status is not changed.
477 - status_change_nid_high is set node id when N_HIGH_MEMORY of nodemask
478 is (will be) set/clear, if this is -1, then nodemask status is not changed.
479 - status_change_nid is set node id when N_MEMORY of nodemask is (will be)
480 set/clear. It means a new(memoryless) node gets new memory by online and a
481 node loses all memory. If this is -1, then nodemask status is not changed.
492 NOTIFY_BAD is used as response to the MEM_GOING_ONLINE, MEM_GOING_OFFLINE,
493 MEM_ONLINE, or MEM_OFFLINE action to cancel hotplugging. It stops
501 - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
503 - showing memory block and physical device relationship.
504 - test and make it better memory offlining.
505 - support HugeTLB page migration and offlining.
506 - memmap removing at memory offline.
507 - physical remove memory.