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

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Message-ID: <alpine.DEB.2.10.1604061512460.10401@chino.kir.corp.google.com>
Date:	Wed, 6 Apr 2016 15:13:27 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Vitaly Kuznetsov <vkuznets@...hat.com>, linux-mm@...ck.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jonathan Corbet <corbet@....net>,
	Dan Williams <dan.j.williams@...el.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>,
	David Vrabel <david.vrabel@...rix.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Lennart Poettering <lennart@...ttering.net>
Subject: Re: [PATCH 0/2] memory_hotplug: introduce config and command line
 options to set the default onlining policy

On Wed, 6 Apr 2016, Andrew Morton wrote:

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

I don't understand why initscripts simply cannot crawl sysfs memory blocks 
and online them for the same behavior.