linux-kernel - Re: [PATCH 1 of 6] hotplug-memory: refactor online_pages to separate zone growth from page onlining

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Date:	Thu, 03 Apr 2008 18:32:09 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <clameter@....com>
Subject: Re: [PATCH 1 of 6] hotplug-memory: refactor online_pages to	separate
 zone growth from page onlining

Dave Hansen wrote:
> On Thu, 2008-04-03 at 17:05 -0700, Jeremy Fitzhardinge wrote:
>   
>> +int prepare_online_pages(unsigned long pfn, unsigned long nr_pages)
>> +{
>> +       int ret = notify_going_online(pfn, nr_pages);
>> +       if (ret)
>> +               return ret;
>> +
>> +       grow_zone_span(pfn, pfn+nr_pages);
>>         return 0;
>> +}
>>     
>
> OK, after seeing this used in the Xen driver, I'm even less a fan of the
> name.  Mostly because it doesn't actually prepare *pages* to be onlined.
> It prepares the zones/pgdats and notifies that pages might soon be
> online.  Can you think of any better names?
>
> grow_and_notify...??
>   

Does it even need to be a separately visible function?  Could it just be 
part of add_memory()?  Is there any reason delay doing it until 
online_pages()?

That way online_pages() can return to being the one-stop function to 
online all the pages, making mark_pages_online() redundant.

> It's also a bit funky because you're calling the online notifiers, but
> you're not actually onlining the pages, yet.  Does that have any
> repercussions?

No.  It will always call the GOING_ONLINE notifier, but it will only 
call the ONLINE notifier if it actually bulk-onlines all the pages.  In 
my page-by-page case, it will never end up calling the ONLINE notifier.  
I could call it repeatedly for each page, but I'm not sure how useful 
that is (the lack of any users of the ONLINE notifier makes it hard to 
judge).

    J
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