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From:   Pavel Tatashin <pasha.tatashin@soleen.com>
Date:   Thu, 18 Jul 2019 12:43:33 -0400
Message-ID: <CA+CK2bDG8xNAgn++8uTOP9OsuEzynm=-Gkb+oUj9DKB8sEudiA@mail.gmail.com>
Subject: Re: [PATCH 1/1] mm/memory_hotplug: Adds option to hot-add memory in ZONE_MOVABLE
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Leonardo Bras <leonardo@linux.ibm.com>,
        Oscar Salvador <osalvador@suse.de>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Pasha Tatashin <Pavel.Tatashin@microsoft.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
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Sender: linux-kernel-owner@vger.kernel.org
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> > Just trying to understand, if kernel parameters is the preferable
> > method, why do we even have
> >
> > MEMORY_HOTPLUG_DEFAULT_ONLINE
>
> I have some opinion on this one TBH. I have even tried to remove it. The
> config option has been added to workaround hotplug issues for some
> memory balloning usecases where it was believed that the memory consumed
> for the memory hotadd (struct pages) could get machine to OOM before
> userspace manages to online it. So I would be more than happy to remove
> it but there were some objections in the past. Maybe the work by Oscar
> to allocate memmaps from the hotplugged memory can finally put an end to
> this gross hack.

Makes sense, thank you for the background info.

Pasha