admin-guide/mm/memory-hotplug.rst

20 - The physical memory available to a machine can be adjusted at runtime, up- or
25 - Replacing hardware, such as DIMMs or whole NUMA nodes, without downtime. One
28 - Reducing energy consumption either by physically unplugging memory modules or
32 used to expose persistent memory, other performance-differentiated memory and
39 ------------------------------
54 ------------------------
71 --------------------------
94 ------------------
112 --------------
152 -------------------------------
154 If auto-onlining of memory blocks isn't enabled, user-space has to manually
183 ------------------------------------
185 The kernel can be configured to try auto-onlining of newly added memory blocks.
189 The configured auto-online behavior can be observed via::
193 Auto-onlining can be enabled by writing ``online``, ``online_kernel`` or
201 Modifying the auto-online behavior will only affect all subsequently added
206   In corner cases, auto-onlining can fail. The kernel won't retry. Note that
207   auto-onlining is not expected to fail in default configurations.
215 -----------------------
248 ------------------------------------
250 The state (online/offline/going-offline) of a memory block can be observed
270 ------------------------------------------
279 ``auto_online_blocks`` read-write: set or get the default state of new memory
280 		       blocks; configure auto-onlining.
287 ``block_size_bytes``   read-only: the size in bytes of a memory block.
288 ``probe``	       write-only: add (probe) selected memory blocks manually
293 ``uevent``	       read-write: generic udev file for device subsystems.
294 ``crash_hotplug``      read-only: when changes to the system memory map
313 ------------------------------------
338 ``online``	    read-write: simplified interface to trigger onlining /
341 ``phys_device``	    read-only: legacy interface only ever used on s390x to
343 ``phys_index``	    read-only: the memory block id (XXX).
344 ``removable``	    read-only: legacy interface that indicated whether a memory
348 ``state``	    read-write: advanced interface to trigger onlining /
359 		    When reading, ``online``, ``offline`` and ``going-offline``
361 ``uevent``	    read-write: generic uevent file for devices.
362 ``valid_zones``     read-only: when a block is online, shows the zone it
389 	/sys/devices/system/node/node0/memory9 -> ../../memory/memory9
393 	/sys/devices/system/memory/memory9/node0 -> ../../node/node0
396 -----------------------
402 ``memhp_default_state``	 configure auto-onlining by essentially setting
405 			 using the ``contig-zones`` online policy. When
411 See Documentation/admin-guide/kernel-parameters.txt for a more generic
415 ------------------
431 ``memmap_on_memory``		 read-write: Allocate memory for the memmap from
456 ``online_policy``		 read-write: Set the basic policy used for
459 				 ``contig-zones`` has been the kernel default
465 				 When set to ``contig-zones``, the kernel will
473 				 When set to ``auto-movable``, the kernel will
487 				 firmware-provided memory map early during boot
489 				 added and onlined  later during boot (such as
490 				 done by virtio-mem or by some hypervisors
496 				 belonging to a virtio-mem device will be
498 				 special-casing units of memory blocks that can
504 ``auto_movable_ratio``		 read-write: Set the maximum MOVABLE:KERNEL
505 				 memory ratio in % for the ``auto-movable``
532 				 hotplugged by a virtio-mem device that got
535 				 virtio-mem device.
536 ``auto_movable_numa_aware``	 read-write: Configure whether the
537 				 ``auto_movable_ratio`` in the ``auto-movable``
571 ---------------
582 long-term pinning of pages, might not be able to deal with ZONE_MOVABLE at all.
591 ----------------------------------
599 ZONE_MOVABLE, especially when fine-tuning zone ratios:
601 - Having a lot of offline memory blocks. Even offline memory blocks consume
605 - Memory ballooning without balloon compaction is incompatible with
606   ZONE_MOVABLE. Only some implementations, such as virtio-balloon and
614 - Gigantic pages are unmovable, resulting in user space consuming a
617 - Huge pages are unmovable when an architectures does not support huge
620 - Page tables are unmovable. Excessive swapping, mapping extremely large
626 - In certain DAX configurations the memory map for the device memory will be
629 - KASAN can have a significant memory overhead, for example, consuming 1/8th of
632 - Long-term pinning of pages. Techniques that rely on long-term pinnings
642 By default, all the memory configured at boot time is managed by the kernel
645 To enable ZONE_MOVABLE to include the memory present at boot and to control the
648 Documentation/admin-guide/kernel-parameters.rst for their description.
651 ---------------------------------
656 - Memory blocks with memory holes; this applies to memory blocks present during
657   boot and can apply to memory blocks hotplugged via the XEN balloon and the
658   Hyper-V balloon.
660 - Mixed NUMA nodes and mixed zones within a single memory block prevent memory
661   offlining; this applies to memory blocks present during boot only.
663 - Special memory blocks prevented by the system from getting offlined. Examples
664   include any memory available during boot on arm64 or memory blocks spanning
666   during boot only.
668 - Memory blocks overlapping with CMA areas cannot be offlined, this applies to
669   memory blocks present during boot only.
671 - Concurrent activity that operates on the same physical memory area, such as
674 - Out of memory when dissolving huge pages, especially when HugeTLB Vmemmap
689 (-> BUG), memory offlining will keep retrying until it eventually succeeds.