Re: [PATCH 0/6] mm: make movable onlining suck less

[Reza Arbab]

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.

> From 1b08ecef3e8ebcef585fe8f2b23155be54cce335 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@xxxxxxxx>
> Date: Tue, 4 Apr 2017 21:09:00 +0200
> Subject: [PATCH] mm, hotplug: get rid of zone/node shrinking
...%<...
> ---
> mm/memory_hotplug.c | 207 ----------------------------------------------------
> 1 file changed, 207 deletions(-)

Okay, getting further. With this I can again repeatedly add and remove, 
but now I'm seeing a weird variation of that earlier issue:

1. add_memory(), online_movable
  /sys/devices/system/node/nodeX/memoryY symlinks are created.

2. offline, remove_memory()
  The node is offlined, since all memory has been removed, so all of
  /sys/devices/system/node/nodeX is gone. This is normal.

3. add_memory(), online_movable
  The node is onlined, so /sys/devices/system/node/nodeX is recreated,
  and the memory is added, but just like earlier in this email thread,
  the memoryY links are not there.

--
Reza Arbab