linux-kernel - Re: [PATCH v3] MM: CMA: add a simple kernel module as the helper to test CMA

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Date:	Wed, 7 Mar 2012 18:55:46 +0800
From:	Barry Song <21cnbao@...il.com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	Barry Song <Barry.Song@....com>,
	Cong Wang <xiyou.wangcong@...il.com>, workgroup.linux@....com,
	Barry Song <Baohua.Song@....com>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, m.szyprowski@...sung.com
Subject: Re: [PATCH v3] MM: CMA: add a simple kernel module as the helper to
 test CMA

2012/3/7 Michal Nazarewicz <mina86@...a86.com>:
>> On 03/07/2012 11:14 AM, Barry Song wrote:
>>>
>>> Any write request to /dev/cma_test will let the module to allocate memory
>>> from
>>> CMA, for example:
>>>
>>> 1st time
>>> $ echo 1024>  /dev/cma_test
>>> will require cma_test to request 1MB(1024KB)
>>> 2nd time
>>> $ echo 2048>  /dev/cma_test
>>> will require cma_test to request 2MB(2048KB)
>>>
>>> Any read request to /dev/cma_test will let the module to free the 1st
>>> valid
>>> memory from CMA, for example:
>>>
>>> 1st time
>>> $ cat /dev/cma_test
>>> will require cma_test to free the 1MB allocated in the first write
>>> request
>>> 2nd time
>>> $ cat /dev/cma_test
>>> will require cma_test to free the 2MB allocated in the second write
>>> request
>
>
> On Wed, 07 Mar 2012 05:14:36 +0100, Cong Wang <xiyou.wangcong@...il.com>
> wrote:
>>
>> Any reason why using /dev not /proc or /sys?
>
>
> Because /proc is for processes and /sys is for stable, documented APIs.
>
> If anything, debugfs might make some sense, but since the module needs
> struct
> device anyway, it can just register a misc device, which is simpler and does
> not require debugfs to be compiled.

Michal, thanks for clarification. actually after i sent my mail to
agree Cong's /proc might be ok, then i had more thinking, i came back
to think the original /dev is better since anyway we need to device to
alloc CM.
then we let the device's read/write to handle alloc/free. it is much
more direct for a test module.

>
> --
> Best regards,                                         _     _
> .o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
> ..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
> ooo +----<email/xmpp: mpn@...gle.com>--------------ooO--(_)--Ooo--
>

-barry
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