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Date: Tue, 2 Oct 2018 16:59:22 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH] migration/mm: Add WARN_ON to try_offline_node
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To: Michael Bringmann <mwb@linux.vnet.ibm.com>
Cc: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>, Thomas Falcon <tlfalcon@linux.vnet.ibm.com>, Kees Cook <keescook@chromium.org>, Mathieu Malaterre <malat@debian.org>, Pavel Tatashin <pasha.tatashin@oracle.com>, Nicholas Piggin <npiggin@gmail.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>, Juliet Kim <minkim@us.ibm.com>, Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>, Nathan Fontenot <nfont@linux.vnet.ibm.com>, Andrew Morton <akpm@linux-foundation.org>, YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>, linuxppc-dev@lists.ozlabs.org, Dan Williams <dan.j.williams@intel.com>, Oscar Salvador <osalvador@suse.de>

On Tue 02-10-18 09:51:40, Michael Bringmann wrote:
[...]
> When the device-tree affinity attributes have changed for memory,
> the 'nid' affinity calculated points to a different node for the
> memory block than the one used to install it, previously on the
> source system.  The newly calculated 'nid' affinity may not yet
> be initialized on the target system.  The current memory tracking
> mechanisms do not record the node to which a memory block was
> associated when it was added.  Nathan is looking at adding this
> feature to the new implementation of LMBs, but it is not there
> yet, and won't be present in earlier kernels without backporting a
> significant number of changes.

Then the patch you have proposed here just papers over a real issue, no?
IIUC then you simply do not remove the memory if you lose the race.
-- 
Michal Hocko
SUSE Labs