From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1423164AbaDKQYZ (ORCPT <rfc822;w@1wt.eu>);
	Fri, 11 Apr 2014 12:24:25 -0400
Received: from mga02.intel.com ([134.134.136.20]:25187 "EHLO mga02.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1422998AbaDKQYX (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Fri, 11 Apr 2014 12:24:23 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="4.97,842,1389772800"; 
   d="scan'208";a="519227917"
Message-ID: <53481724.8020304@intel.com>
Date: Fri, 11 Apr 2014 09:24:04 -0700
From: Dave Hansen <dave.hansen@intel.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0
MIME-Version: 1.0
To: David Rientjes <rientjes@google.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
CC: drepper@gmail.com, anatol.pomozov@gmail.com, jkosina@suse.cz,
        akpm@linux-foundation.org, xemul@parallels.com,
        paul.gortmaker@windriver.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH] drivers/base/node.c: export physical address range of
 given node (Re: NUMA node information for pages)
References: <87eh1ix7g0.fsf@x240.local.i-did-not-set--mail-host-address--so-tickle-me> <533a1563.ad318c0a.6a93.182bSMTPIN_ADDED_BROKEN@mx.google.com> <CAOPLpQc8R2SfTB+=BsMa09tcQ-iBNJHg+tGnPK-9EDH1M47MJw@mail.gmail.com> <5343806c.100cc30a.0461.ffffc401SMTPIN_ADDED_BROKEN@mx.google.com> <alpine.DEB.2.02.1404091734060.1857@chino.kir.corp.google.com> <5345fe27.82dab40a.0831.0af9SMTPIN_ADDED_BROKEN@mx.google.com> <alpine.DEB.2.02.1404101500280.11995@chino.kir.corp.google.com> <53474709.e59ec20a.3bd5.3b91SMTPIN_ADDED_BROKEN@mx.google.com> <alpine.DEB.2.02.1404110325210.30610@chino.kir.corp.google.com>
In-Reply-To: <alpine.DEB.2.02.1404110325210.30610@chino.kir.corp.google.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 04/11/2014 04:00 AM, David Rientjes wrote:
> On Thu, 10 Apr 2014, Naoya Horiguchi wrote:
>> > Yes, that's right, but it seems to me that just node_start_pfn and node_end_pfn
>> > is not enough because there can be holes (without any page struct backed) inside
>> > [node_start_pfn, node_end_pfn), and it's not aware of memory hotplug.
>> > 
> So?  Who cares if there are non-addressable holes in part of the span?  
> Ulrich, correct me if I'm wrong, but it seems you're looking for just a 
> address-to-nodeid mapping (or pfn-to-nodeid mapping) and aren't actually 
> expecting that there are no holes in a node for things like acpi or I/O or 
> reserved memory.
...
> I think trying to represent holes and handling different memory models and 
> hotplug in special ways is complete overkill.

This isn't just about memory hotplug or different memory models.  There
are systems out there today, in production, that have layouts like this:

|------Node0-----|
     |------Node1-----|

and this:

|------Node0-----|
     |-Node1-|

For those systems, this interface has no meaning.  Given a page in the
shared-span areas, this interface provides no way to figure out which
node it is in.

If you want a non-portable hack that just works on one system, I'd
suggest parsing the existing firmware tables.