linux-kernel - Re: [patch 4/4] x86: interleave emulated nodes over physical nodes

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Date:	Fri, 9 Oct 2009 02:34:17 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Ankita Garg <ankita@...ibm.com>,
	Len Brown <len.brown@...el.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 4/4] x86: interleave emulated nodes over physical nodes

On Thu, 1 Oct 2009, Ingo Molnar wrote:

> > This patch interleaves emulated nodes over the system's physical 
> > nodes. This is required for interleave optimizations since 
> > mempolicies, for example, operate by iterating over a nodemask and act 
> > without knowledge of node distances.  It can also be used for testing 
> > memory latencies and NUMA bugs in the kernel.
> > 
> > There're a couple of ways to do this:
> > 
> >  - divide the number of emulated nodes by the number of physical nodes
> >    and allocate the result on each physical node, or
> > 
> >  - allocate each successive emulated node on a different physical node
> >    until all memory is exhausted.
> > 
> > The disadvantage of the first option is, depending on the asymmetry in 
> > node capacities of each physical node, emulated nodes may 
> > substantially differ in size on a particular physical node compared to 
> > another.
> > 
> > The disadvantage of the second option is, also depending on the 
> > asymmetry in node capacities of each physical node, there may be more 
> > emulated nodes allocated on a single physical node as another.
> > 
> > This patch implements the second option; we sacrifice the possibility 
> > that we may have slightly more emulated nodes on a particular physical 
> > node compared to another in lieu of node size asymmetry.
> > 
> >  [ Note that "node capacity" of a physical node is not only a function of
> >    its addressable range, but also is affected by subtracting out the
> >    amount of reserved memory over that range.  NUMA emulation only deals
> >    with available, non-reserved memory quantities. ]
> > 
> > We ensure there is at least a minimal amount of available memory
> > allocated to each node.  We also make sure that at least this amount of
> > available memory is available in ZONE_DMA32 for any node that includes
> > both ZONE_DMA32 and ZONE_NORMAL.
> > 
> > This patch also cleans the emulation code up by no longer passing the
> > statically allocated struct bootnode array among the various functions.
> > This init.data array is not allocated on the stack since it may be very
> > large and thus it may be accessed at file scope.
> > 
> > The WARN_ON() for nodes_cover_memory() when faking proximity domains is
> > removed since it relies on successive nodes always having greater start
> > addresses than previous nodes; with interleaving this is no longer always
> > true.
> > 
> > Cc: Yinghai Lu <yinghai@...nel.org>
> > Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
> > Cc: Ankita Garg <ankita@...ibm.com>
> > Signed-off-by: David Rientjes <rientjes@...gle.com>
> > ---
> >  arch/x86/mm/numa_64.c |  211 ++++++++++++++++++++++++++++++++++++++++++------
> >  arch/x86/mm/srat_64.c |    1 -
> >  2 files changed, 184 insertions(+), 28 deletions(-)
> 
> Looks very nice. Peter, Thomas, any objections against queueing this up 
> in the x86 tree for more testing?
> 

Thanks!  Do you know when this will be merged?
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