linux-kernel - Re: [RFC PATCH 0/5] mm, memory_hotplug: allocate memmap from hotadded memory

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Message-Id: <20170731143521.5809a6ca@thinkpad>
Date:   Mon, 31 Jul 2017 14:35:21 +0200
From:   Gerald Schaefer <gerald.schaefer@...ibm.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Jerome Glisse <jglisse@...hat.com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        qiuxishi@...wei.com, Kani Toshimitsu <toshi.kani@....com>,
        slaoub@...il.com, Joonsoo Kim <js1304@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        Will Deacon <will.deacon@....com>, gerald.schaefer@...ibm.com
Subject: Re: [RFC PATCH 0/5] mm, memory_hotplug: allocate memmap from
 hotadded memory

On Fri, 28 Jul 2017 14:19:41 +0200
Michal Hocko <mhocko@...nel.org> wrote:

> On Thu 27-07-17 08:56:52, Michal Hocko wrote:
> > On Wed 26-07-17 17:06:59, Jerome Glisse wrote:
> > [...]
> > > This does not seems to be an opt-in change ie if i am reading patch 3
> > > correctly if an altmap is not provided to __add_pages() you fallback
> > > to allocating from begining of zone. This will not work with HMM ie
> > > device private memory. So at very least i would like to see some way
> > > to opt-out of this. Maybe a new argument like bool forbid_altmap ?
> > 
> > OK, I see! I will think about how to make a sane api for that.
> 
> This is what I came up with. s390 guys mentioned that I cannot simply
> use the new range at this stage yet. This will need probably some other
> changes but I guess we want an opt-in approach with an arch veto in general.
> 
> So what do you think about the following? Only x86 is update now and I
> will split it into two parts but the idea should be clear at least.

This looks good, and the kernel will also boot again on s390 when applied
on top of the other 5 patches (plus adding the s390 part here).

Regards,
Gerald