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

From: Yinghai Lu <yinghai@kernel.org>
To: Tejun Heo <tj@kernel.org>
Cc: Tang Chen <tangchen@cn.fujitsu.com>,
	Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Renninger <trenn@suse.de>,
	Jiang Liu <jiang.liu@huawei.com>,
	Wen Congyang <wency@cn.fujitsu.com>,
	Lai Jiangshan <laijs@cn.fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
	Mel Gorman <mgorman@suse.de>, Minchan Kim <minchan@kernel.org>,
	mina86@mina86.com, gong.chen@linux.intel.com,
	Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>,
	lwoodman@redhat.com, Rik van Riel <riel@redhat.com>,
	jweiner@redhat.com, Prarit Bhargava <prarit@redhat.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	linux-doc@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>,
	David Rientjes <rientjes@google.com>
Subject: Re: [Part1 PATCH v5 16/22] x86, mm, numa: Move numa emulation handling down.
Date: Wed, 19 Jun 2013 14:25:41 -0700	[thread overview]
Message-ID: <CAE9FiQVYwiFXanN0tbR=_=VDUn75DvfGsFPHbrYsPM3CWBaaQg@mail.gmail.com> (raw)
In-Reply-To: <CAE9FiQVVGdDMxO5RmHSzAcB_cu49EQFiNLxswS7U0Nt5-J774w@mail.gmail.com>

On Mon, Jun 17, 2013 at 11:22 PM, Yinghai Lu <yinghai@kernel.org> wrote:
> On Mon, Jun 17, 2013 at 6:58 PM, Tejun Heo <tj@kernel.org> wrote:
>> On Thu, Jun 13, 2013 at 09:03:03PM +0800, Tang Chen wrote:
>>> From: Yinghai Lu <yinghai@kernel.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.

the new numa_emulation will call numa_check_memblks at first before
touch numa_meminfo.
if it fails, numa_meminfo is not touched, so that should not a problem.

>
> 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.

For numa emulation fail sequence, want to double check what should be
right seuence:

on and before 2.6.38:
   emulation ==> acpi ==> amd ==> dummy
so if emulation with wrong input, will fall back to acpi numa.

from 2.6.39
   acpi (emulation) ==> amd (emulation) ==> dummy (emulation)
if emulation with wrong input, it will fall back to next numa discovery.

after my patchset
will be acpi ==> amd ==> dummy
          emulation.
the new emulation will call numa_check_memblks at first before touch
numa_meminfo.
anyway if emulation fails, numa_meminfo is not touched.

so this change looks like right change.

Thanks

Yinghai