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authorMike Rapoport <rppt@linux.vnet.ibm.com>2018-10-05 01:11:01 +0300
committerJonathan Corbet <corbet@lwn.net>2018-10-07 18:16:25 +0300
commit98cee6742c80e35274bab06c5fa1141fe0abd910 (patch)
tree57251c239acfd821cc2d836e688eeda4ea1b614d /Documentation/core-api
parent6bf53999a3a269d5d27bb636602f6788e1bb4dd0 (diff)
downloadlinux-98cee6742c80e35274bab06c5fa1141fe0abd910.tar.xz
docs/vm: split memory hotplug notifier description to Documentation/core-api
The memory hotplug notifier description is about kernel internals rather than admin/user visible API. Place it appropriately. Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/core-api')
-rw-r--r--Documentation/core-api/index.rst2
-rw-r--r--Documentation/core-api/memory-hotplug-notifier.rst84
2 files changed, 86 insertions, 0 deletions
diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index 165d76886d73..4f8a4266eb7c 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -32,6 +32,8 @@ Core utilities
gfp_mask-from-fs-io
timekeeping
boot-time-mm
+ memory-hotplug-notifier
+
Interfaces for kernel debugging
===============================
diff --git a/Documentation/core-api/memory-hotplug-notifier.rst b/Documentation/core-api/memory-hotplug-notifier.rst
new file mode 100644
index 000000000000..35347cc3a43a
--- /dev/null
+++ b/Documentation/core-api/memory-hotplug-notifier.rst
@@ -0,0 +1,84 @@
+.. _memory_hotplug_notifier:
+
+=============================
+Memory hotplug event notifier
+=============================
+
+Hotplugging events are sent to a notification queue.
+
+There are six types of notification defined in ``include/linux/memory.h``:
+
+MEM_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.
+
+MEM_CANCEL_ONLINE
+ Generated if MEM_GOING_ONLINE fails.
+
+MEM_ONLINE
+ Generated when memory has successfully brought online. The callback may
+ allocate pages from the new memory.
+
+MEM_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 block.
+
+MEM_CANCEL_OFFLINE
+ Generated if MEM_GOING_OFFLINE fails. Memory is available again from
+ the memory block that we attempted to offline.
+
+MEM_OFFLINE
+ Generated after offlining memory is complete.
+
+A callback routine can be registered by calling::
+
+ hotplug_memory_notifier(callback_func, priority)
+
+Callback functions with higher values of priority are called before callback
+functions with lower values.
+
+A callback function must have the following prototype::
+
+ int callback_func(
+ struct notifier_block *self, unsigned long action, void *arg);
+
+The first argument of the callback function (self) is a pointer to the block
+of the notifier chain that points to the callback function itself.
+The second argument (action) is one of the event types described above.
+The third argument (arg) passes a 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_high;
+ 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_high is set node id when N_HIGH_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_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.
+
+The callback routine shall return one of the values
+NOTIFY_DONE, NOTIFY_OK, NOTIFY_BAD, NOTIFY_STOP
+defined in ``include/linux/notifier.h``
+
+NOTIFY_DONE and NOTIFY_OK have no effect on the further processing.
+
+NOTIFY_BAD is used as response to the MEM_GOING_ONLINE, MEM_GOING_OFFLINE,
+MEM_ONLINE, or MEM_OFFLINE action to cancel hotplugging. It stops
+further processing of the notification queue.
+
+NOTIFY_STOP stops further processing of the notification queue.