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

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Message-ID: <CA+CK2bA9_B8siPCSSdrN_yecGZZy82UNx7P=QK8N5GuPjto1HQ@mail.gmail.com>
Date:   Thu, 18 Jul 2019 12:45:36 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Leonardo Bras <leonardo@...ux.ibm.com>
Cc:     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>,
        Michal Hocko <mhocko@...e.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 12:04 PM Leonardo Bras <leonardo@...ux.ibm.com> wrote:
>
> On Thu, 2019-07-18 at 08:19 -0400, Pavel Tatashin wrote:
> > On Wed, Jul 17, 2019 at 10:42 PM Leonardo Bras <leonardo@...ux.ibm.com> wrote:
> > > Adds an option on kernel config to make hot-added memory online in
> > > ZONE_MOVABLE by default.
> > >
> > > This would be great in systems with MEMORY_HOTPLUG_DEFAULT_ONLINE=y by
> > > allowing to choose which zone it will be auto-onlined
> >
> > This is a desired feature. From reading the code it looks to me that
> > auto-selection of online method type should be done in
> > memory_subsys_online().
> >
> > When it is called from device online, mem->online_type should be -1:
> >
> > if (mem->online_type < 0)
> >      mem->online_type = MMOP_ONLINE_KEEP;
> >
> > Change it to:
> > if (mem->online_type < 0)
> >      mem->online_type = MMOP_DEFAULT_ONLINE_TYPE;
> >
> > And in "linux/memory_hotplug.h"
> > #ifdef CONFIG_MEMORY_HOTPLUG_MOVABLE
> > #define MMOP_DEFAULT_ONLINE_TYPE MMOP_ONLINE_MOVABLE
> > #else
> > #define MMOP_DEFAULT_ONLINE_TYPE MMOP_ONLINE_KEEP
> > #endif
> >
> > Could be expanded to support MMOP_ONLINE_KERNEL as well.
> >
> > Pasha
>
> Thanks for the suggestions Pasha,
>
> I was made aware there is a kernel boot option "movable_node" that
> already creates the behavior I was trying to reproduce.

I agree with others, no need to duplicate this functionality in a
config, and Michal in a separate e-mail explained the reasons why we
have MEMORY_HOTPLUG_DEFAULT_ONLINE.

>
> I was thinking of changing my patch in order to add a config option
> that makes this behavior default (i.e. not need to pass it as a boot
> parameter.
>
> Do you think that it would still be a desired feature?
>
> Regards,
>
> Leonardo Brás