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

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Date:   Wed, 5 Apr 2017 15:55:29 -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 Wed, Apr 05, 2017 at 06:34:39PM +0200, Michal Hocko wrote:
>This is really interesting. Because add_memory_resource does the
>following
>	/* call arch's memory hotadd */
>	ret = arch_add_memory(nid, start, size);
>
>	if (ret < 0)
>		goto error;
>
>	/* we online node here. we can't roll back from here. */
>	node_set_online(nid);
>
>so we are setting the node online _after_ arch_add_memory but the code
>which adds those sysfs file is called from
>
>arch_add_memory
>  __add_pages
>    __add_section
>      register_new_memory
>        register_mem_sect_under_node
>          node_online check

Okay, so it turns out the original code ends up creating the sysfs links 
not here, but just a little bit afterwards.

add_memory
  add_memory_resource
    arch_add_memory
      [your quoted stack trace above]
    ...
    set_node_online
    ...
    register_one_node
      link_mem_sections
	register_mem_sect_under_node

The reason they're not getting created now is because 
NODE_DATA(nid)->node_spanned_pages = 0 at this point.

link_mem_sections: nid=1, start_pfn=0x10000, end_pfn=0x10000

This is another uninitialized situation, like the one with 
node_start_pfn which caused my removal crash. Except here I'm not sure 
the correct place to splice in and set it.

-- 
Reza Arbab