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

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Date:	Fri, 21 Jan 2011 02:52:34 +0900
From:	KyongHo Cho <pullip.linux@...il.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	linux-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

On Fri, Jan 21, 2011 at 2:44 AM, Minchan Kim <minchan.kim@...il.com> wrote:
> Fix linux-arm-kernel address.
>
Thank you!
Too late in the night:)

> On Fri, Jan 21, 2011 at 2:43 AM, Minchan Kim <minchan.kim@...il.com> wrote:
>> 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
>>
>
>
>
> --
> Kind regards,
> Minchan Kim
>
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