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Subject[Patch 001/002] Make description of memory hotplug notifier in document

Add description about event notification callback routine to the document.

Signed-off-by: Yasunori Goto <>

Documentation/memory-hotplug.txt | 56 ++++++++++++++++++++++++++++++++++++---
1 file changed, 53 insertions(+), 3 deletions(-)

Index: current/Documentation/memory-hotplug.txt
--- current.orig/Documentation/memory-hotplug.txt
+++ current/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 +309,68 @@ 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.
+ This is notified before memory online. If some structures must be prepared
+ for new memory, it should be done at this event's callback.
+ The new onlining memory can't be used yet.
+ If memory online fails, this event is notified for rollback of setting at
+ (Currently, this event is notified only the case which a callback routine
+ This event is called when memory online is completed. The page allocator uses
+ new memory area before this notification. In other words, callback routine
+ use new memory area via page allocator.
+ The failures of callbacks of this notification will be ignored.
+ This is notified on halfway of memory offline. The offlining pages are
+ isolated. In other words, the page allocater doesn't allocate new pages from
+ offlining memory area at this time. If callback routine freed some pages,
+ they are not used by the page allocator.
+ This is good place for shrinking cache. (If possible, it is desirable to
+ migrate to other area.)
+ If memory offline fails, this event is notified for rollback against
+ MEMORY_GOING_OFFLINE. The page allocator will use target memory area after
+ this callback again.
+ This is notified after memory offline completed. The failures of callbacks
+ of this notification will be ignored. Callback routine can return structures
+ for offlined memory.
+ If the node which has offlined memory,
+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_change_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 lose 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.
Yasunori Goto

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