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

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Date:	Wed, 1 Oct 2008 09:51:05 -0700
From:	Gary Hade <garyhade@...ibm.com>
To:	Yasunori Goto <y-goto@...fujitsu.com>
Cc:	Gary Hade <garyhade@...ibm.com>,
	Dave Hansen <dave@...ux.vnet.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 Wed, Oct 01, 2008 at 11:48:29AM +0900, Yasunori Goto wrote:
> > 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.
> 
> 
> It may be possible that one section is divided to different node in theory.
> (I don't know really there is...)
> 
> But, the cause of my trouble differs from it.
> There is a memory hole which is occupied by firmware.
> So, the memory map of my box is here.
> 
> ----
> early_node_map[3] active PFN ranges
>     0: 0x00000100 -> 0x00006d00
>     0: 0x00408000 -> 0x00410000
>     1: 0x01200400 -> 0x01210000
> ----
> 
> memmap_init() initializes from start_pfn (to end_pfn).
> So, the memmaps for this first hole (0x1200000 - 0x12003ff) are not initialized,
> and node id is not set for them. This is true cause.

Thanks for the clarification.  I think we need to cover both the
theoretical single memory section spanning multiple nodes case
and your memory hole/memory section intersection case.

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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