linux-kernel - Re: [PATCH 14/21] x86, acpi, numa: Reserve hotpluggable memory at early time.

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Date:	Thu, 25 Jul 2013 10:13:21 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	tglx@...utronix.de, mingo@...e.hu, hpa@...or.com,
	akpm@...ux-foundation.org, trenn@...e.de, yinghai@...nel.org,
	jiang.liu@...wei.com, wency@...fujitsu.com, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, izumi.taku@...fujitsu.com,
	mgorman@...e.de, minchan@...nel.org, mina86@...a86.com,
	gong.chen@...ux.intel.com, vasilis.liaskovitis@...fitbricks.com,
	lwoodman@...hat.com, riel@...hat.com, jweiner@...hat.com,
	prarit@...hat.com, zhangyanfei@...fujitsu.com,
	yanghy@...fujitsu.com, x86@...nel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 14/21] x86, acpi, numa: Reserve hotpluggable memory at
 early time.

On 07/24/2013 05:32 AM, Tejun Heo wrote:
> On Tue, Jul 23, 2013 at 04:55:57PM -0400, Tejun Heo wrote:
>> On Fri, Jul 19, 2013 at 03:59:27PM +0800, Tang Chen wrote:
>>> +		/*
>>> +		 * In such an early time, we don't have nid. We specify pxm
>>> +		 * instead of MAX_NUMNODES to prevent memblock merging regions
>>> +		 * on different nodes. And later modify pxm to nid when nid is
>>> +		 * mapped so that we can arrange ZONE_MOVABLE on different
>>> +		 * nodes.
>>> +		 */
>>> +		memblock_reserve_hotpluggable(base_address, length, pxm);
>>
>> This is rather hacky.  Why not just introduce MEMBLOCK_NO_MERGE flag?

The original thinking is to merge regions with the same nid. So I used pxm.
And then refresh the nid field when nids are mapped.

I will try to introduce MEMBLOCK_NO_MERGE and make it less hacky.

>
> Also, if memblock is gonna know about hotplug memory, why not just let
> it control its allocation too instead of blocking it by reserving it
> from outside?  These are all pretty general memory hotplug logic which
> doesn't have much to do with acpi and I think too much is implemented
> on the acpi side.

At the very beginning, a long time ago, we just did this.
Please refer to: https://lkml.org/lkml/2012/12/10/656

In order to let memblock control the allocation, we have to store the
hotpluggable ranges somewhere, and keep the allocated range out of the
hotpluggable regions. I just think reserving the hotpluggable regions
and then memblock won't allocate them. No need to do any other limitation.

And also, the acpi side modification in this patch-set is to get SRAT
and parse it. I think most of the logic in 
acpi_reserve_hotpluggable_memory()
is necessary. I don't think letting memblock control the allocation will
make the acpi side easier.

Thanks.
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