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@xxxxxxxxxxxxx> --- 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
