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Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks

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On Mon 27-02-17 12:25:10, Heiko Carstens wrote:
> On Mon, Feb 27, 2017 at 11:02:09AM +0100, Vitaly Kuznetsov wrote:
> > A couple of other thoughts:
> > 1) Having all newly added memory online ASAP is probably what people
> > want for all virtual machines.
> 
> This is not true for s390. On s390 we have "standby" memory that a guest
> sees and potentially may use if it sets it online. Every guest that sets
> memory offline contributes to the hypervisor's standby memory pool, while
> onlining standby memory takes memory away from the standby pool.
> 
> The use-case is that a system administrator in advance knows the maximum
> size a guest will ever have and also defines how much memory should be used
> at boot time. The difference is standby memory.
> 
> Auto-onlining of standby memory is the last thing we want.
> 
> > Unfortunately, we have additional complexity with memory zones
> > (ZONE_NORMAL, ZONE_MOVABLE) and in some cases manual intervention is
> > required. Especially, when further unplug is expected.
> 
> This also is a reason why auto-onlining doesn't seem be the best way.

Can you imagine any situation when somebody actually might want to have
this knob enabled? From what I understand it doesn't seem to be the
case.

-- 
Michal Hocko
SUSE Labs

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Thread

[RFC PATCH] mm, hotplug: get rid of auto_online_blocks Michal Hocko <mhocko@kernel.org> - 2017-02-27 11:10 +0100
  Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-02-27 11:10 +0100
    Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Michal Hocko <mhocko@kernel.org> - 2017-02-27 11:40 +0100
      Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-02-27 12:00 +0100
        Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-02-27 14:20 +0100
        Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Michal Hocko <mhocko@kernel.org> - 2017-02-27 16:30 +0100
    Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-02-27 12:30 +0100
      Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Vitaly Kuznetsov <vkuznets@redhat.com> - 2017-02-27 13:00 +0100
      Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Michal Hocko <mhocko@kernel.org> - 2017-02-27 16:50 +0100
        Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-02-28 14:40 +0100
  Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Michal Hocko <mhocko@kernel.org> - 2017-02-27 19:30 +0100
  Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Reza Arbab <arbab@linux.vnet.ibm.com> - 2017-02-28 00:40 +0100

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