linux-kernel - Re: [PATCH] mm/memory hotplug: print the last vmemmap region at the end of hot add memory

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Message-Id: <20150608163053.c481d9a5057513130f760910@linux-foundation.org>
Date:	Mon, 8 Jun 2015 16:30:53 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Zhu Guihua <zhugh.fnst@...fujitsu.com>
Cc:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<vbabka@...e.cz>, <rientjes@...gle.com>,
	<n-horiguchi@...jp.nec.com>, <zhenzhang.zhang@...wei.com>,
	<wangnan0@...wei.com>, <fabf@...net.be>
Subject: Re: [PATCH] mm/memory hotplug: print the last vmemmap region at the
 end of hot add memory

On Mon, 8 Jun 2015 14:44:41 +0800 Zhu Guihua <zhugh.fnst@...fujitsu.com> wrote:

> When hot add two nodes continuously, we found the vmemmap region info is a
> bit messed. The last region of node 2 is printed when node 3 hot added,
> like the following:
> Initmem setup node 2 [mem 0x0000000000000000-0xffffffffffffffff]
>  On node 2 totalpages: 0
>  Built 2 zonelists in Node order, mobility grouping on.  Total pages: 16090539
>  Policy zone: Normal
>  init_memory_mapping: [mem 0x40000000000-0x407ffffffff]
>   [mem 0x40000000000-0x407ffffffff] page 1G
>   [ffffea1000000000-ffffea10001fffff] PMD -> [ffff8a077d800000-ffff8a077d9fffff] on node 2
>   [ffffea1000200000-ffffea10003fffff] PMD -> [ffff8a077de00000-ffff8a077dffffff] on node 2
> ...
>   [ffffea101f600000-ffffea101f9fffff] PMD -> [ffff8a074ac00000-ffff8a074affffff] on node 2
>   [ffffea101fa00000-ffffea101fdfffff] PMD -> [ffff8a074a800000-ffff8a074abfffff] on node 2
> Initmem setup node 3 [mem 0x0000000000000000-0xffffffffffffffff]
>  On node 3 totalpages: 0
>  Built 3 zonelists in Node order, mobility grouping on.  Total pages: 16090539
>  Policy zone: Normal
>  init_memory_mapping: [mem 0x60000000000-0x607ffffffff]
>   [mem 0x60000000000-0x607ffffffff] page 1G
>   [ffffea101fe00000-ffffea101fffffff] PMD -> [ffff8a074a400000-ffff8a074a5fffff] on node 2 <=== node 2 ???
>   [ffffea1800000000-ffffea18001fffff] PMD -> [ffff8a074a600000-ffff8a074a7fffff] on node 3
>   [ffffea1800200000-ffffea18005fffff] PMD -> [ffff8a074a000000-ffff8a074a3fffff] on node 3
>   [ffffea1800600000-ffffea18009fffff] PMD -> [ffff8a0749c00000-ffff8a0749ffffff] on node 3
> ...
> 
> The cause is the last region was missed at the and of hot add memory, and
> p_start, p_end, node_start were not reset, so when hot add memory to a new
> node, it will consider they are not contiguous blocks and print the
> previous one. So we print the last vmemmap region at the end of hot add
> memory to avoid the confusion.
> 
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -513,6 +513,7 @@ int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
>  			break;
>  		err = 0;
>  	}
> +	vmemmap_populate_print_last();
>  
>  	return err;
>  }

vmemmap_populate_print_last() is only available on x86_64, when
CONFIG_SPARSEMEM_VMEMMAP=y.  Are you sure this won't break builds?

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