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Date: Wed, 6 Apr 2016 11:53:34 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        Dan Williams <dan.j.williams@intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>, David Vrabel <david.vrabel@citrix.com>,
        David Rientjes <rientjes@google.com>,
        Igor Mammedov <imammedo@redhat.com>,
        Lennart Poettering <lennart@poettering.net>
Subject: Re: [PATCH 0/2] memory_hotplug: introduce config and command line
 options to set the default onlining policy
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On Wed,  6 Apr 2016 15:45:10 +0200 Vitaly Kuznetsov <vkuznets@redhat.com> wrote:

> This patchset continues the work I started with:
> 
> commit 31bc3858ea3ebcc3157b3f5f0e624c5962f5a7a6
> Author: Vitaly Kuznetsov <vkuznets@redhat.com>
> 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.