On 03/18/20 at 02:54pm, Michal Hocko wrote:

On Wed 18-03-20 21:05:17, Baoquan He wrote:

quoted

On 03/17/20 at 11:49am, David Hildenbrand wrote:

quoted

Distributions nowadays use udev rules ([1] [2]) to specify if and
how to online hotplugged memory. The rules seem to get more complex with
many special cases. Due to the various special cases,
CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE cannot be used. All memory hotplug
is handled via udev rules.

Everytime we hotplug memory, the udev rule will come to the same
conclusion. Especially Hyper-V (but also soon virtio-mem) add a lot of
memory in separate memory blocks and wait for memory to get onlined by user
space before continuing to add more memory blocks (to not add memory faster
than it is getting onlined). This of course slows down the whole memory
hotplug process.

To make the job of distributions easier and to avoid udev rules that get
more and more complicated, let's extend the mechanism provided by
- /sys/devices/system/memory/auto_online_blocks
- "memhp_default_state=" on the kernel cmdline
to be able to specify also "online_movable" as well as "online_kernel"

This patch series looks good, thanks. Since Andrew has merged it to -mm again,
I won't add my Reviewed-by to bother. 

JFYI, Andrew usually adds R-b or A-b tags as they are posted.

Got it, thanks for telling.