Re: [PATCH 0/2] memory_hotplug: introduce config and command line options to set the default onlining policy

[Vitaly Kuznetsov]

David Rientjes <rientjes@xxxxxxxxxx> writes:

> On Wed, 6 Apr 2016, Andrew Morton wrote:
>
>> > This patchset continues the work I started with:
>> > 
>> > commit 31bc3858ea3ebcc3157b3f5f0e624c5962f5a7a6
>> > Author: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>> > Date:   Tue Mar 15 14:56:48 2016 -0700
>> > 
>> >     memory-hotplug: add automatic onlining policy for the newly added memory
>> > 
>> > Initially I was going to stop there and bring the policy setting logic to
>> > userspace. I met two issues on this way:
>> > 
>> > 1) It is possible to have memory hotplugged at boot (e.g. with QEMU). These
>> >    blocks stay offlined if we turn the onlining policy on by userspace.
>> > 
>> > 2) My attempt to bring this policy setting to systemd failed, systemd
>> >    maintainers suggest to change the default in kernel or ... to use tmpfiles.d
>> >    to alter the policy (which looks like a hack to me): 
>> >    https://github.com/systemd/systemd/pull/2938
>> 
>> That discussion really didn't come to a conclusion and I don't
>> understand why you consider Lennert's "recommended way" to be a hack?
>> 
>> > Here I suggest to add a config option to set the default value for the policy
>> > and a kernel command line parameter to make the override.
>> 
>> But the patchset looks pretty reasonable regardless of the above.
>> 
>
> I don't understand why initscripts simply cannot crawl sysfs memory blocks 
> and online them for the same behavior.

Yes, they can. With this patchset I don't bring any new features, it's
rather a convenience so linux distros can make memory hotplug work
'out of the box' without such distro-specific initscripts. Memory
hotplug is a standard feature of all major virt technologies so I think
it's pretty reasonable to have an option to make it work 'by default'
available.

-- 
  Vitaly