linux-kernel - Re: [PATCH] mm: add node physical memory range to sysfs

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Message-ID: <1355361524.5255.9.camel@buesod1.americas.hpqcorp.net>
Date:	Wed, 12 Dec 2012 17:18:44 -0800
From:	Davidlohr Bueso <davidlohr.bueso@...com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: add node physical memory range to sysfs

On Fri, 2012-12-07 at 16:17 -0800, Dave Hansen wrote:
> On 12/07/2012 03:51 PM, Andrew Morton wrote:
> >> > +static ssize_t node_read_memrange(struct device *dev,
> >> > +				  struct device_attribute *attr, char *buf)
> >> > +{
> >> > +	int nid = dev->id;
> >> > +	unsigned long start_pfn = NODE_DATA(nid)->node_start_pfn;
> >> > +	unsigned long end_pfn = start_pfn + NODE_DATA(nid)->node_spanned_pages;
> > hm.  Is this correct for all for
> > FLATMEM/SPARSEMEM/SPARSEMEM_VMEMMAP/DISCONTIGME/etc?
> 
> It's not _wrong_ per se, but it's not super precise, either.
> 
> The problem is, it's quite valid to have these node_start/spanned ranges
> overlap between two or more nodes on some hardware.  So, if the desired
> purpose is to map nodes to DIMMs, then this can only accomplish this on
> _some_ hardware, not all.  It would be completely useless for that
> purpose for some configurations.
> 
> Seems like the better way to do this would be to expose the DIMMs
> themselves in some way, and then map _those_ back to a node.
> 

Good point, and from a DIMM perspective, I agree, and will look into
this. However, IMHO, having the range of physical addresses for every
node still provides valuable information, from a NUMA point of view. For
example, dealing with node related e820 mappings.

Andrew, with the documentation patch, would you be wiling to pickup a v2
of this?

Thanks,
Davidlohr

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