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

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Date:   Tue, 4 Apr 2017 16:43:39 -0500
From:   Reza Arbab <arbab@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        Tang Chen <tangchen@...fujitsu.com>, qiuxishi@...wei.com,
        Kani Toshimitsu <toshi.kani@....com>, slaoub@...il.com,
        Joonsoo Kim <js1304@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Zhang Zhen <zhenzhang.zhang@...wei.com>,
        David Rientjes <rientjes@...gle.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dan Williams <dan.j.williams@...il.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Lai Jiangshan <laijs@...fujitsu.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 0/6] mm: make movable onlining suck less

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@...e.com>
>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