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>

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.