linux-kernel - Re: [RFC PATCH v5 16/19] memory-hotplug: free memmap of sparse-vmemmap

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Message-ID: <5018C817.80509@cn.fujitsu.com>
Date:	Wed, 01 Aug 2012 14:09:27 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	gerald.schaefer@...ibm.com
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	rientjes@...gle.com, liuj97@...il.com, len.brown@...el.com,
	benh@...nel.crashing.org, paulus@...ba.org, cl@...ux.com,
	minchan.kim@...il.com, akpm@...ux-foundation.org,
	kosaki.motohiro@...fujitsu.com,
	Yasuaki ISIMATU <isimatu.yasuaki@...fujitsu.com>
Subject: Re: [RFC PATCH v5 16/19] memory-hotplug: free memmap of sparse-vmemmap

At 07/31/2012 08:22 PM, Gerald Schaefer Wrote:
> On Fri, 27 Jul 2012 18:34:38 +0800
> Wen Congyang <wency@...fujitsu.com> wrote:
> 
>> From: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>>
>> All pages of virtual mapping in removed memory cannot be freed, since
>> some pages used as PGD/PUD includes not only removed memory but also
>> other memory. So the patch checks whether page can be freed or not.
>>
>> How to check whether page can be freed or not?
>>  1. When removing memory, the page structs of the revmoved memory are
>> filled with 0FD.
>>  2. All page structs are filled with 0xFD on PT/PMD, PT/PMD can be
>> cleared. In this case, the page used as PT/PMD can be freed.
>>
>> Applying patch, __remove_section() of CONFIG_SPARSEMEM_VMEMMAP is
>> integrated into one. So __remove_section() of
>> CONFIG_SPARSEMEM_VMEMMAP is deleted.
> 
> There should also be generic or dummy versions of the functions
> vmemmap_free_bootmem(), vmemmap_kfree() and
> register_page_bootmem_memmap(). It doesn't compile on other
> archtitectures than x86 as it is now:
> 
> mm/built-in.o: In function `sparse_remove_one_section':
> (.text+0x49fa6): undefined reference to `vmemmap_free_bootmem'
> mm/built-in.o: In function `sparse_remove_one_section':
> (.text+0x49fcc): undefined reference to `vmemmap_kfree'
> mm/built-in.o: In function `register_page_bootmem_info_node':
> (.text+0x57c06): undefined reference to `register_page_bootmem_memmap'
> mm/built-in.o: In function `sparse_add_one_section':
> (.meminit.text+0x2506): undefined reference to `vmemmap_kfree'
> mm/built-in.o: In function `sparse_add_one_section':
> (.meminit.text+0x2528): undefined reference to `vmemmap_kfree'
> make: *** [vmlinux] Error 1
> 
> 

Thanks for testing. I will fix it.

Wen Congyang
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