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Date: Wed, 5 Apr 2017 11:24:27 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 0/6] mm: make movable onlining suck less
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To: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Vlastimil Babka <vbabka@suse.cz>, Andrea Arcangeli <aarcange@redhat.com>, Yasuaki Ishimatsu <yasu.isimatu@gmail.com>, Tang Chen <tangchen@cn.fujitsu.com>, qiuxishi@huawei.com, Kani Toshimitsu <toshi.kani@hpe.com>, slaoub@gmail.com, Joonsoo Kim <js1304@gmail.com>, Andi Kleen <ak@linux.intel.com>, Zhang Zhen <zhenzhang.zhang@huawei.com>, David Rientjes <rientjes@google.com>, Daniel Kiper <daniel.kiper@oracle.com>, Igor Mammedov <imammedo@redhat.com>, Vitaly Kuznetsov <vkuznets@redhat.com>, LKML <linux-kernel@vger.kernel.org>, Chris Metcalf <cmetcalf@mellanox.com>, Dan Williams <dan.j.williams@gmail.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>

On Wed 05-04-17 08:42:39, Michal Hocko wrote:
> On Tue 04-04-17 16:43:39, Reza Arbab wrote:
> > On Tue, Apr 04, 2017 at 09:41:22PM +0200, Michal Hocko wrote:
> > >On Tue 04-04-17 13:30:13, Reza Arbab wrote:
> > >>I think I found another edge case.  You
> > >>get an oops when removing all of a node's memory:
> > >>
> > >>__nr_to_section
> > >>__pfn_to_section
> > >>find_biggest_section_pfn
> > >>shrink_pgdat_span
> > >>__remove_zone
> > >>__remove_section
> > >>__remove_pages
> > >>arch_remove_memory
> > >>remove_memory
> > >
> > >Is this something new or an old issue? I believe the state after the
> > >online should be the same as before. So if you onlined the full node
> > >then there shouldn't be any difference. Let me have a look...
> > 
> > It's new. Without this patchset, I can repeatedly
> > add_memory()->online_movable->offline->remove_memory() all of a node's
> > memory.
> 
> This is quite unexpected because the code obviously cannot handle the
> first memory section. Could you paste /proc/zoneinfo and
> grep . -r /sys/devices/system/memory/auto_online_blocks/memory*, after
> onlining for both patched and unpatched kernels?

Btw. how do you test this? I am really surprised you managed to
hotremove such a low pfn range.
-- 
Michal Hocko
SUSE Labs

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