Date: Mon, 31 Jul 2017 14:53:19 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Jerome Glisse <jglisse@redhat.com>, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Reza Arbab <arbab@linux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, qiuxishi@huawei.com,
        Kani Toshimitsu <toshi.kani@hpe.com>, slaoub@gmail.com,
        Joonsoo Kim <js1304@gmail.com>, Andi Kleen <ak@linux.intel.com>,
        Daniel Kiper <daniel.kiper@oracle.com>,
        Igor Mammedov <imammedo@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Paul Mackerras <paulus@samba.org>,
        Thomas Gleixner <tglx@linutronix.de>, Tony Luck <tony.luck@intel.com>,
        Will Deacon <will.deacon@arm.com>
Subject: Re: [RFC PATCH 0/5] mm, memory_hotplug: allocate memmap from
 hotadded memory
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References: <20170726083333.17754-1-mhocko@kernel.org>
 <20170726210657.GE21717@redhat.com>
 <20170727065652.GE20970@dhcp22.suse.cz>
 <20170728121941.GL2274@dhcp22.suse.cz>
 <20170731143521.5809a6ca@thinkpad>
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On Mon 31-07-17 14:35:21, Gerald Schaefer wrote:
> On Fri, 28 Jul 2017 14:19:41 +0200
> Michal Hocko <mhocko@kernel.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).

Thanks for testing Gerald! I am still undecided whether the arch code
should veto MHP_RANGE_ACCESSIBLE if it cannot be supported or just set
it when it is supported. My last post did the later but the first one
sounds like a more clear API to me. I will keep thinking about it.

Anyway, did you have any chance to consider mapping the new physical
memory range inside arch_add_memory rather than during online on s390?
-- 
Michal Hocko
SUSE Labs