On 14.05.19 10:23, Mike Rapoport wrote: > 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. Looks sane, but the future work part is really outdated, can we remove this completely? > > 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. ... that already works if I am not completely missing the point here > + - showing memory block and physical device relationship. ... that is available for s390x only AFAIK > + - test and make it better memory offlining. ... no big news ;) > + - support HugeTLB page migration and offlining. ... I remember that Oscar was doing something in that area, Oscar? > + - memmap removing at memory offline. ... no, we don't want this. However, we should properly clean up zone information when offlining > + - physical remove memory. ... I don't even understand what that means. I'd vote for removing the future work part, this is pretty outdated. -- Thanks, David / dhildenb
