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Date: Wed, 5 Apr 2017 11:24:27 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH 0/6] mm: make movable onlining suck less
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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