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

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Message-ID: <AANLkTi=MizfGY4koMmRHprts6Ji3ofeSZPBBTiH1FDcn@mail.gmail.com>
Date:	Fri, 21 Jan 2011 02:44:09 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KyongHo Cho <pullip.linux@...il.com>,
	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

Fix linux-arm-kernel address.

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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