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SubjectRe: [PATCH v2 8/8] mm/memory_hotplug: allow to specify a default online_type
On 17.03.20 12:01, Michal Hocko wrote:
> On Tue 17-03-20 11:49:42, David Hildenbrand wrote:
>> 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 user space to come up with the same answer.
>> E.g., Hyper-V 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. This waiting
>> slows down adding of a bigger amount of memory.
>> 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/system/memory/auto_online_blocks
>> just like we are able to specify for a single memory block via
>> /sys/devices/system/memory/memoryX/state
>> Reviewed-by: Wei Yang <>
>> Cc: Greg Kroah-Hartman <>
>> Cc: Andrew Morton <>
>> Cc: Michal Hocko <>
>> Cc: Oscar Salvador <>
>> Cc: "Rafael J. Wysocki" <>
>> Cc: Baoquan He <>
>> Cc: Wei Yang <>
>> Signed-off-by: David Hildenbrand <>
> As I've said earlier and several times already, I really dislike this
> interface. But it is fact that this patch doesn't make it any worse.
> Quite contrary, so feel free to add
> Acked-by: Michal Hocko <>

Thanks Michal!


David / dhildenb

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