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Date: Wed, 26 Jul 2017 14:30:41 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
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        Paul Mackerras <paulus@samba.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Gerald Schaefer <gerald.schaefer@de.ibm.com>
Subject: Re: [RFC PATCH 3/5] mm, memory_hotplug: allocate memmap from the
 added memory range for sparse-vmemmap
Message-ID: <20170726123040.GO2981@dhcp22.suse.cz>
References: <20170726083333.17754-1-mhocko@kernel.org>
 <20170726083333.17754-4-mhocko@kernel.org>
 <20170726114539.GG3218@osiris>
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On Wed 26-07-17 13:45:39, Heiko Carstens wrote:
[...]
> In general I do like your idea, however if I understand your patches
> correctly we might have an ordering problem on s390: it is not possible to
> access hot-added memory on s390 before it is online (MEM_GOING_ONLINE
> succeeded).

Could you point me to the code please? I cannot seem to find the
notifier which implements that.

> On MEM_GOING_ONLINE we ask the hypervisor to back the potential available
> hot-added memory region with physical pages. Accessing those ranges before
> that will result in an exception.

Can we make the range which backs the memmap range available? E.g from
s390 specific __vmemmap_populate path?
 
> However with your approach the memory is still allocated when add_memory()
> is being called, correct? That wouldn't be a change to the current
> behaviour; except for the ordering problem outlined above.

Could you be more specific please? I do not change when the memmap is
allocated.

-- 
Michal Hocko
SUSE Labs