From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx160.postini.com [74.125.245.160]) by kanga.kvack.org (Postfix) with SMTP id BDFF96B0002 for ; Fri, 29 Mar 2013 12:40:16 -0400 (EDT) Date: Fri, 29 Mar 2013 17:40:14 +0100 From: Sam Ravnborg Subject: Re: [PATCH v3, part4 38/39] mm/hotplug: prepare for removing num_physpages Message-ID: <20130329164014.GA6266@merkur.ravnborg.org> References: <1364313298-17336-1-git-send-email-jiang.liu@huawei.com> <1364313298-17336-39-git-send-email-jiang.liu@huawei.com> <20130329111856.GA3824@merkur.ravnborg.org> <5155B517.3040501@gmail.com> <20130329161700.GA6201@merkur.ravnborg.org> <5155C196.5020909@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5155C196.5020909@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Jiang Liu Cc: Andrew Morton , David Rientjes , Jiang Liu , Wen Congyang , Mel Gorman , Minchan Kim , KAMEZAWA Hiroyuki , Michal Hocko , James Bottomley , Sergei Shtylyov , David Howells , Mark Salter , Jianguo Wu , linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Tang Chen , Yasuaki Ishimatsu On Sat, Mar 30, 2013 at 12:30:14AM +0800, Jiang Liu wrote: > On 03/30/2013 12:17 AM, Sam Ravnborg wrote: > >>>> 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. > Hi Sam, > I haven't gotten your point yet here. > Function __online_page_set_limits() was only used to update the global variable > num_physpages, and one of the goals of this patch set is to get rid of num_physpages. > So I think it won't break Xen balloon driver. > Please refer to the patch here, which eventually kills num_physpages. > http://marc.info/?l=linux-mm&m=136431387813309&w=2 I assumed that num_physpages was used run-time to check for the available number of pages. And __online_page_set_limits() were used to reduced the number of online pages. But a quick grep did not reveal any such use. So it looks OK - thanks for the clarification. Sam -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org