From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx203.postini.com [74.125.245.203]) by kanga.kvack.org (Postfix) with SMTP id 5D7A46B0002 for ; Fri, 29 Mar 2013 12:42:27 -0400 (EDT) Received: by mail-pd0-f174.google.com with SMTP id p12so319916pdj.33 for ; Fri, 29 Mar 2013 09:42:26 -0700 (PDT) Message-ID: <5155C466.9040406@gmail.com> Date: Sat, 30 Mar 2013 00:42:14 +0800 From: Jiang Liu MIME-Version: 1.0 Subject: Re: [PATCH v3, part4 38/39] mm/hotplug: prepare for removing num_physpages 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> <20130329164014.GA6266@merkur.ravnborg.org> In-Reply-To: <20130329164014.GA6266@merkur.ravnborg.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Sam Ravnborg 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 03/30/2013 12:40 AM, Sam Ravnborg wrote: > 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. Yeah, we have a patch to replace num_physpages with totalram_pages for runtime access, please refer to: http://marc.info/?l=linux-mm&m=136431351413052&w=2 > > 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