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Subject[PATCH] docs: reorder memory-hotplug documentation
Date
The "Locking Internals" section of the memory-hotplug documentation is
duplicated in admin-guide and core-api. Drop the admin-guide copy as
locking internals does not belong there.

While on it, move the "Future Work" section to the core-api part.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
Documentation/admin-guide/mm/memory-hotplug.rst | 51 -------------------------
Documentation/core-api/memory-hotplug.rst | 11 ++++++
2 files changed, 11 insertions(+), 51 deletions(-)

diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 5c4432c..72090ba 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -391,54 +391,3 @@ Physical memory remove
Need more implementation yet....
- Notification completion of remove works by OS to firmware.
- Guard from remove if not yet.
-
-
-Locking Internals
-=================
-
-When adding/removing memory that uses memory block devices (i.e. ordinary RAM),
-the device_hotplug_lock should be held to:
-
-- synchronize against online/offline requests (e.g. via sysfs). This way, memory
- block devices can only be accessed (.online/.state attributes) by user
- space once memory has been fully added. And when removing memory, we
- know nobody is in critical sections.
-- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC)
-
-Especially, there is a possible lock inversion that is avoided using
-device_hotplug_lock when adding memory and user space tries to online that
-memory faster than expected:
-
-- device_online() will first take the device_lock(), followed by
- mem_hotplug_lock
-- add_memory_resource() will first take the mem_hotplug_lock, followed by
- the device_lock() (while creating the devices, during bus_add_device()).
-
-As the device is visible to user space before taking the device_lock(), this
-can result in a lock inversion.
-
-onlining/offlining of memory should be done via device_online()/
-device_offline() - to make sure it is properly synchronized to actions
-via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type)
-
-When adding/removing/onlining/offlining memory or adding/removing
-heterogeneous/device memory, we should always hold the mem_hotplug_lock in
-write mode to serialise memory hotplug (e.g. access to global/zone
-variables).
-
-In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read
-mode allows for a quite efficient get_online_mems/put_online_mems
-implementation, so code accessing memory can protect from that memory
-vanishing.
-
-
-Future Work
-===========
-
- - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
- sysctl or new control file.
- - showing memory block and physical device relationship.
- - test and make it better memory offlining.
- - support HugeTLB page migration and offlining.
- - memmap removing at memory offline.
- - physical remove memory.
diff --git a/Documentation/core-api/memory-hotplug.rst b/Documentation/core-api/memory-hotplug.rst
index de7467e..e08be1c 100644
--- a/Documentation/core-api/memory-hotplug.rst
+++ b/Documentation/core-api/memory-hotplug.rst
@@ -123,3 +123,14 @@ In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read
mode allows for a quite efficient get_online_mems/put_online_mems
implementation, so code accessing memory can protect from that memory
vanishing.
+
+Future Work
+===========
+
+ - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
+ sysctl or new control file.
+ - showing memory block and physical device relationship.
+ - test and make it better memory offlining.
+ - support HugeTLB page migration and offlining.
+ - memmap removing at memory offline.
+ - physical remove memory.
--
2.7.4
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