Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6867c9310d5dab6897638a89c7e31addfcb22043
Commit: 6867c9310d5dab6897638a89c7e31addfcb22043
Parent: 925796e0ed6fe529770ba71454c58c8d4d8a5ac4
Author: Yasunori Goto [EMAIL PROTECTED]
AuthorDate: Fri Aug 10 13:00:59 2007 -0700
Committer: Linus Torvalds [EMAIL PROTECTED]
CommitDate: Sat Aug 11 15:47:41 2007 -0700
Memory hotplug document
This is add a document for memory hotplug to describe How to use and
Current status.
Signed-off-by: KAMEZAWA Hiroyuki [EMAIL PROTECTED]
Signed-off-by: Yasunori Goto [EMAIL PROTECTED]
Signed-off-by: Andrew Morton [EMAIL PROTECTED]
Signed-off-by: Linus Torvalds [EMAIL PROTECTED]
---
Documentation/memory-hotplug.txt | 322 ++
1 files changed, 322 insertions(+), 0 deletions(-)
diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
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+==
+Memory Hotplug
+==
+
+Last Updated: Jul 28 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
+be changed often.
+
+1. Introduction
+ 1.1 purpose of memory hotplug
+ 1.2. Phases of memory hotplug
+ 1.3. Unit of Memory online/offline operation
+2. Kernel Configuration
+3. sysfs files for memory hotplug
+4. Physical memory hot-add phase
+ 4.1 Hardware(Firmware) Support
+ 4.2 Notify memory hot-add event by hand
+5. Logical Memory hot-add phase
+ 5.1. State of memory
+ 5.2. How to online memory
+6. Logical memory remove
+ 6.1 Memory offline and ZONE_MOVABLE
+ 6.2. How to offline memory
+7. Physical memory remove
+8. Future Work List
+
+Note(1): x86_64's has special implementation for memory hotplug.
+ This text does not describe it.
+Note(2): This text assumes that sysfs is mounted at /sys.
+
+
+---
+1. Introduction
+---
+
+1.1 purpose of memory hotplug
+
+Memory Hotplug allows users to increase/decrease the amount of memory.
+Generally, there are two purposes.
+
+(A) For changing the amount of memory.
+This is to allow a feature like capacity on demand.
+(B) For installing/removing DIMMs or NUMA-nodes physically.
+This is to exchange DIMMs/NUMA-nodes, reduce power consumption, etc.
+
+(A) is required by highly virtualized environments and (B) is required by
+hardware which supports memory power management.
+
+Linux memory hotplug is designed for both purpose.
+
+
+1.2. Phases of memory hotplug
+---
+There are 2 phases in Memory Hotplug.
+ 1) Physical Memory Hotplug phase
+ 2) Logical Memory Hotplug phase.
+
+The First phase is to communicate hardware/firmware and make/erase
+environment for hotplugged memory. Basically, this phase is necessary
+for the purpose (B), but this is good phase for communication between
+highly virtualized environments too.
+
+When memory is hotplugged, the kernel recognizes new memory, makes new memory
+management tables, and makes sysfs files for new memory's operation.
+
+If firmware supports notification of connection of new memory to OS,
+this phase is triggered automatically. ACPI can notify this event. If not,
+probe operation by system administration is used instead.
+(see Section 4.).
+
+Logical Memory Hotplug phase is to change memory state into
+avaiable/unavailable for users. Amount of memory from user's view is
+changed by this phase. The kernel makes all memory in it as free pages
+when a memory range is available.
+
+In this document, this phase is described as online/offline.
+
+Logical Memory Hotplug phase is triggred by write of sysfs file by system
+administrator. For the hot-add case, it must be executed after Physical Hotplug
+phase by hand.
+(However, if you writes udev's hotplug scripts for memory hotplug, these
+ phases can be execute in seamless way.)
+
+
+1.3. Unit of Memory online/offline operation
+
+Memory hotplug uses SPARSEMEM memory model. SPARSEMEM divides the whole memory
+into chunks of the same size. The chunk is called a section. The size of
+a section is architecture dependent. For example, power uses 16MiB, ia64 uses
+1GiB. The unit of online/offline operation is one section. (see Section 3.)
+
+To determine the size of sections, please read this file:
+
+/sys/devices/system/memory/block_size_bytes
+
+This file shows the size of sections in byte.
+
+---
+2. Kernel Configuration
+---
+To use memory hotplug feature, kernel must be compiled with following
+config options.
+
+- For all memory hotplug
+Memory model - Sparse Memory (CONFIG_SPARSEMEM)
+Allow for memory hot-add (CONFIG_MEMORY_HOTPLUG)
+
+- To enable memory removal, the followings are also necessary
+Allow for memory hot remove
