Re: [PATCH v1 5/5] mm/memory_hotplug: allow to specify a default online_type

On 11.03.20 15:26, Wei Yang wrote:

On Wed, Mar 11, 2020 at 01:30:26PM +0100, David Hildenbrand wrote:

quoted

For now, distributions implement advanced udev rules to essentially
- Don't online any hotplugged memory (s390x)
- Online all memory to ZONE_NORMAL (e.g., most virt environments like
 hyperv)
- Online all memory to ZONE_MOVABLE in case the zone imbalance is taken
 care of (e.g., bare metal, special virt environments)

In summary: All memory is usually onlined the same way, however, the
kernel always has to ask userspace to come up with the same answer.
E.g., HyperV always waits for a memory block to get onlined before
continuing, otherwise it might end up adding memory faster than
hotplugging it, which can result in strange OOM situations.

Let's allow to specify a default online_type, not just "online" and
"offline". This allows distributions to configure the default online_type
when booting up and be done with it.

We can now specify "offline", "online", "online_movable" and
"online_kernel" via
- "memhp_default_state=" on the kernel cmdline
- /sys/devices/systemn/memory/auto_online_blocks
just like we are able to specify for a single memory block via
/sys/devices/systemn/memory/memoryX/state

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Baoquan He <redacted>
Cc: Wei Yang <redacted>
Signed-off-by: David Hildenbrand <redacted>

Ok, I got the reason to leave the change on string compare here.

Thanks for your *very fast* review! :)


-- 
Thanks,

David / dhildenb