linux-kernel - Re: [Part1 PATCH v5 16/22] x86, mm, numa: Move numa emulation handling down.

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Message-ID: <CAE9FiQUUcprDmEtTiTAZXWjWP9MCmjF+onFD9S2OcZi=Mr54QQ@mail.gmail.com>
Date:	Tue, 18 Jun 2013 00:13:52 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Tang Chen <tangchen@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Renninger <trenn@...e.de>,
	Jiang Liu <jiang.liu@...wei.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
	mina86@...a86.com, gong.chen@...ux.intel.com,
	vasilis.liaskovitis@...fitbricks.com, lwoodman@...hat.com,
	Rik van Riel <riel@...hat.com>, jweiner@...hat.com,
	Prarit Bhargava <prarit@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	linux-doc@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [Part1 PATCH v5 16/22] x86, mm, numa: Move numa emulation
 handling down.

On Mon, Jun 17, 2013 at 11:22 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Mon, Jun 17, 2013 at 6:58 PM, Tejun Heo <tj@...nel.org> wrote:
>> On Thu, Jun 13, 2013 at 09:03:03PM +0800, Tang Chen wrote:
>>> From: Yinghai Lu <yinghai@...nel.org>
>>>
>>> numa_emulation() needs to allocate buffer for new numa_meminfo
>>> and distance matrix, so execute it later in x86_numa_init().
>>>
>>> Also we change the behavoir:
>>>       - before this patch, if user input wrong data in command
>>>         line, it will fall back to next numa probing or disabling
>>>         numa.
>>>       - after this patch, if user input wrong data in command line,
>>>         it will stay with numa info probed from previous probing,
>>>         like ACPI SRAT or amd_numa.
>>>
>>> We need to call numa_check_memblks to reject wrong user inputs early
>>> so that we can keep the original numa_meminfo not changed.
>>
>> So, this is another very subtle ordering you're adding without any
>> comment and I'm not sure it even makes sense because the function can
>> fail after that point.
>
> Yes, if it fail, we will stay with current numa info from firmware.
> That looks like right behavior.
>
> Before this patch, it will fail to next numa way like if acpi srat + user
> input fail, it will try to go with amd_numa then try apply user info.
>
>>
>> I'm getting really doubtful about this whole approach of carefully
>> splitting discovery and registration.  It's inherently fragile like
>> hell and the poor documentation makes it a lot worse.  I'm gonna reply
>> to the head message.
>
> Maybe look at the patch is not clear enough, but if looks at the final changed
> code it would be more clear.

update the patches from 1-15 with your review.

git://git.kernel.org/pub/scm/linux/kernel/git/yinghai/linux-yinghai.git
for-x86-mm

https://git.kernel.org/cgit/linux/kernel/git/yinghai/linux-yinghai.git/log/?h=for-x86-mm

Yinghai
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