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: <557965D1.7020009@cn.fujitsu.com>
Date:	Thu, 11 Jun 2015 18:41:21 +0800
From:	Zhu Guihua <zhugh.fnst@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 06/10/2015 04:29 AM, Andrew Morton wrote:
> On Tue, 9 Jun 2015 11:41:28 +0800 Zhu Guihua <zhugh.fnst@...fujitsu.com> wrote:
>
>>>> --- 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?
>> I tried this on i386 and on x86_64 when CONFIG_SPARSEMEM_VMEMMAP=n ,
>> it builds ok.
> With powerpc:
>
> akpm3:/usr/src/25> make allmodconfig
> akpm3:/usr/src/25> make mm/memory_hotplug.o
> akpm3:/usr/src/25> nm mm/memory_hotplug.o | grep vmemmap_populate_print_last
> 	U .vmemmap_populate_print_last
> akpm3:/usr/src/25> grep -r vmemmap_populate_print_last arch/powerpc
> akpm3:/usr/src/25>
>
> So I think that's going to break.
>
> I expect ia64 will break also, but I didn't investigate.
> .
>

There is
void __weak __meminit vmemmap_populate_print last(void)
in /mm/sparse.c, so I think this won't break builds.

And I found the function was invoked in void __init sparse_init(void) 
without
CONFIG_SPARSEMEM_VMEMMAP=y.

I also tried this on arm, it builds ok too.

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