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

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Date:	Tue, 31 Jul 2012 14:22:51 +0200
From:	Gerald Schaefer <gerald.schaefer@...ibm.com>
To:	Wen Congyang <wency@...fujitsu.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

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

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