linux-kernel - Re: [PATCH] ARM: mm: Regarding section when dealing with meminfo

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Date:	Fri, 21 Jan 2011 02:43:22 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KyongHo Cho <pullip.linux@...il.com>,
	inux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	Kukjin Kim <kgene.kim@...sung.com>,
	Ilho Lee <ilho215.lee@...sung.com>,
	KeyYoung Park <keyyoung.park@...sung.com>,
	KyongHo Cho <pullip.cho@...sung.com>
Subject: Re: [PATCH] ARM: mm: Regarding section when dealing with meminfo

Restore Cced.

On Fri, Jan 21, 2011 at 2:24 AM, KyongHo Cho <pullip.linux@...il.com> wrote:
> On Thu, Jan 20, 2011 at 11:28 PM, Minchan Kim <minchan.kim@...il.com> wrote:
>> On Thu, Jan 20, 2011 at 06:45:39PM +0900, KyongHo Cho wrote:
>>> Sparsemem allows that a bank of memory spans over several adjacent
>>> sections if the start address and the end address of the bank
>>> belong to different sections.
>>> When gathering statictics of physical memory in mem_init() and
>>> show_mem(), this possiblity was not considered.
>>
>> Please write down the result if we doesn't consider this patch.
>> I can understand what happens but for making good description and review,
>> merging easily, it would be better to write down the result without
>> the patch explicitly.
>>
> As we know that each section has its own memmap and
> a contiguous chunk of physical memory that is represented by 'bank' in meminfo
> can be larger than the size of a section.
> "page++" in the current implementation can access invalid memory area.
> The size of the section is 256 MiB in ARM and the number of banks in
> meminfo is 8.
> This means that the maximum size of the physical memory cannot be grow than 2GiB
> to avoid this problem in the current implementation.
> Thus we need to fix the calculation of the last page descriptor in
> terms of sections.
>
> This patch determines the last page descriptor in a memmap with
> min(last_pfn_of_bank, last_pfn_of_current_section)
> If there remains physical memory not consumed, it calculates the last
> page descriptor
> with min(last_pfn_of_bank, last_pfn_of_next_section).
>
>>
>> Hmm.. new ifndef magic makes code readability bad.
>> Couldn't we do it by simple pfn iterator not page and pfn_valid check?
>>
> True.
> We need to consider the implementation again.
> I think the previous implementation gave the importance to the
> efficiency but to the readability.
>

Please consider readability and consistency with other architectures
if we can do. :)
Thanks.

-- 
Kind regards,
Minchan Kim
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