path: root/Documentation/memory-hotplug.txt
diff options
authorYasunori Goto <>2007-10-21 16:41:36 -0700
committerLinus Torvalds <>2007-10-22 08:13:17 -0700
commit10020ca246c55744dad815ad4f15e1f488ca55a8 (patch)
treef848f3c6180b043abc7560e366fd634c468cfa41 /Documentation/memory-hotplug.txt
parenta24e785111a32ccb7cebafd24b1b1cb474ea8e5d (diff)
memory hotplug: document the memory hotplug notifier
Add description about event notification callback routine to the document Signed-off-by: Yasunori Goto <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'Documentation/memory-hotplug.txt')
1 files changed, 55 insertions, 3 deletions
diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
index 5fbcc22c98e9..168117bd6ee8 100644
--- a/Documentation/memory-hotplug.txt
+++ b/Documentation/memory-hotplug.txt
@@ -2,7 +2,8 @@
Memory Hotplug
-Last Updated: Jul 28 2007
+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
@@ -24,7 +25,8 @@ be changed often.
6.1 Memory offline and ZONE_MOVABLE
6.2. How to offline memory
7. Physical memory remove
-8. Future Work List
+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.
@@ -307,8 +309,58 @@ 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 notifer. There are 6 types of notification.
+ 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.
+ Generated if MEMORY_GOING_ONLINE fails.
+ Generated when memory has succesfully brought online. The callback may
+ allocate pages from the new memory.
+ 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.
+ Generated if MEMORY_GOING_OFFLINE fails. Memory is available again from
+ the section that we attempted to 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_cahnge_nid;
+start_pfn is start_pfn of online/offline memory.
+nr_pages is # of pages of online/offline memory.
+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.
-8. Future Work
+9. Future Work
- allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
sysctl or new control file.