linux-kernel - Re: [PATCH v3, part4 38/39] mm/hotplug: prepare for removing num

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Date:	Fri, 29 Mar 2013 17:17:00 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jiang Liu <liuj97@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	David Howells <dhowells@...hat.com>,
	Mark Salter <msalter@...hat.com>,
	Jianguo Wu <wujianguo@...wei.com>, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tang Chen <tangchen@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Subject: Re: [PATCH v3, part4 38/39] mm/hotplug: prepare for removing
	num_physpages

> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >> index 97454b3..9b1b494 100644
> >> --- a/mm/memory_hotplug.c
> >> +++ b/mm/memory_hotplug.c
> >> @@ -751,10 +751,6 @@ EXPORT_SYMBOL_GPL(restore_online_page_callback);
> >>  
> >>  void __online_page_set_limits(struct page *page)
> >>  {
> >> -	unsigned long pfn = page_to_pfn(page);
> >> -
> >> -	if (pfn >= num_physpages)
> >> -		num_physpages = pfn + 1;
> >>  }
> >>  EXPORT_SYMBOL_GPL(__online_page_set_limits);
> > 
> > How can this be correct?
> > With this change __online_page_set_limits() is now a nop.
> Hi Sam,
> 	We will eventually remove the global variable num_physpages in the last patch.
> I kept the nop __online_page_set_limits() because I have a plan to use it to fix other
> bugs in memory hotplug, otherwise it may be killed too.

The xen ballon driver uses __online_page_set_limits for memory
hotplug - so this will break this driver afaics.

	Sam
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