linux-kernel - Re: [PATCH 3/4] mmzone: note that node_size_lock should be manipulated via pgdat_resize

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Date:	Wed, 01 May 2013 15:47:59 -0700
From:	Cody P Schafer <cody@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] mmzone: note that node_size_lock should be manipulated
 via pgdat_resize_lock()

On 05/01/2013 03:42 PM, David Rientjes wrote:
> On Wed, 1 May 2013, Cody P Schafer wrote:
>
>>>> Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>
>>>
>>> Nack, pgdat_resize_unlock() is unnecessary if irqs are known to be
>>> disabled.
>>>
>>
>> All this patch does is is indicate that rather than using node_size_lock
>> directly (as it won't be around without CONFIG_MEMORY_HOTPLUG), one should use
>> the pgdat_resize_[un]lock() helper macros.
>>
>
> I think that's obvious given the lock is surrounded by
> #ifdef CONFIG_MEMORY_HOTPLUG.  The fact remains that hotplug code need not
> use pgdat_resize_lock() if irqs are disabled.
>

Obvious how? This comment is the documentation on how to handle locking 
of pg_data_t, and doesn't mention pgdat_resize_lock() at all. Sure, a 
newcomer would probably find pgdat_resize_lock() eventually, even more 
so if they were interested in performance gains from not re-disabling 
local irqs.

I don't see a convincing reason to omit relevant documentation and make 
it more difficult to find the "right" way to do things.

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