Subject: Re: [PATCH v3 0/8] mm/memory_hotplug: allow to specify a default online_type

From: Baoquan He <[email-masked]>
Date: Fri, 20 Mar 2020 18:01:27 +0800

On 03/19/20 at 02:12pm, David Hildenbrand wrote:
> 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"
> 
> v2 -> v3:
> - "hv_balloon: don't check for memhp_auto_online manually"
> -- init_completion() before register_memory_notifier()
> - Minor typo fix
> 
> v1 -> v2:
> - Tweaked some patch descriptions
> - Added
> -- "powernv/memtrace: always online added memory blocks"
> -- "hv_balloon: don't check for memhp_auto_online manually"
> -- "mm/memory_hotplug: unexport memhp_auto_online"
> - "mm/memory_hotplug: convert memhp_auto_online to store an online_type"
> -- No longer touches hv/memtrace code

Ack the series.

Reviewed-by: Baoquan He <[email-masked]>