linux-kernel - Re: [PATCH 1/1] mm/memory_hotplug: Adds option to hot-add memory in ZONE

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Message-ID: <CA+CK2bBU72owYSXH10LTU8NttvCASPNTNOqFfzA3XweXR3gOTw@mail.gmail.com>
Date:   Thu, 18 Jul 2019 12:11:25 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Leonardo Bras <leonardo@...ux.ibm.com>,
        Oscar Salvador <osalvador@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Pasha Tatashin <Pavel.Tatashin@...rosoft.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH 1/1] mm/memory_hotplug: Adds option to hot-add memory in ZONE_MOVABLE

On Thu, Jul 18, 2019 at 11:57 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Thu 18-07-19 12:50:29, Leonardo Bras wrote:
> > On Thu, 2019-07-18 at 08:12 +0200, Oscar Salvador wrote:
> > > We do already have "movable_node" boot option, which exactly has that
> > > effect.
> > > Any hotplugged range will be placed in ZONE_MOVABLE.
> > Oh, I was not aware of it.
> >
> > > Why do we need yet another option to achieve the same? Was not that
> > > enough for your case?
> > Well, another use of this config could be doing this boot option a
> > default on any given kernel.
> > But in the above case I agree it would be wiser to add the code on
> > movable_node_is_enabled() directly, and not where I did put.
> >
> > What do you think about it?
>
> No further config options please. We do have means a more flexible way
> to achieve movable node onlining so let's use it. Or could you be more
> specific about cases which cannot use the command line option and really
> need a config option to workaround that?

Hi Michal,

Just trying to understand, if kernel parameters is the preferable
method, why do we even have

MEMORY_HOTPLUG_DEFAULT_ONLINE

It is just strange that we have a config to online memory by default
without kernel parameter, but no way to specify how to online it. It
just looks as incomplete interface to me. Perhaps this config should
be removed as well?

Pasha