linux-kernel - Re: [PATCH] mm: show node to memory section relationship with symlinks in sysfs

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Date:	Tue, 30 Sep 2008 12:41:22 -0700
From:	Gary Hade <garyhade@...ibm.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Yasunori Goto <y-goto@...fujitsu.com>,
	Gary Hade <garyhade@...ibm.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Mel Gorman <mel@....ul.ie>, Chris McDermott <lcm@...ibm.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Greg KH <greg@...ah.com>,
	Nish Aravamudan <nish.aravamudan@...il.com>
Subject: Re: [PATCH] mm: show node to memory section relationship with
	symlinks in sysfs

On Tue, Sep 30, 2008 at 08:50:37AM -0700, Dave Hansen wrote:
> On Tue, 2008-09-30 at 17:06 +0900, Yasunori Goto wrote:
> > > +#define section_nr_to_nid(section_nr) pfn_to_nid(section_nr_to_pfn(section_nr))
> > >  #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
> > 
> > If the first page of the section is not valid, then this section_nr_to_nid()
> > doesn't return correct value.
> > 
> > I tested this patch. In my box, the start_pfn of node 1 is 1200400, but 
> > section_nr_to_pfn(mem_blk->phys_index) returns 1200000. As a result,
> > the section is linked to node 0.
> 
> Crap, I was worried about that.
> 
> Gary, this means that we have a N:1 relationship between NUMA nodes and
> sections.  This normally isn't a problem because sections don't really
> care about nodes and they layer underneath them.

So, using Yasunori-san's example the memory section starting at
pfn 1200000 actually resides on both node 0 and node 1.

> 
> We'll probably need multiple symlinks in each section directory.

or perhaps symlinks to the same section directory from >1 node directory.

Gary

-- 
Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503  IBM T/L: 775-4503
garyhade@...ibm.com
http://www.ibm.com/linux/ltc
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