From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Wed, 20 Jan 2010 16:10:53 +0000
Subject: too much memory for node
In-Reply-To: <20100120160525.GW10014@trinity.fluff.org>
References: <20100120153411.GG26562@trinity.fluff.org>
	<20100120155510.GB27507@n2100.arm.linux.org.uk>
	<20100120160525.GW10014@trinity.fluff.org>
Message-ID: <20100120161053.GD27507@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, Jan 20, 2010 at 04:05:25PM +0000, Ben Dooks wrote:
> On Wed, Jan 20, 2010 at 03:55:10PM +0000, Russell King - ARM Linux wrote:
> > On Wed, Jan 20, 2010 at 03:34:11PM +0000, Ben Dooks wrote:
> > > I've been looking at support for a new machine type where the
> > > current system is using DISCONTIGMEM as the 1G memory map has
> > > 4x256M RAM ranges which may not all be filled.
> > 
> > Firstly, use sparsemem, unless you intentionally want to spend more
> > cycles in the kernel.
> 
> Ok, any idea if that will fix the problem in this case?

It _may_ do, because it doesn't have the concept of NUMA nodes (which
is what discontigmem is all about.)

> Should I send a patch to detect bad DISCONTIGMEM setup? I think that
> a check of PHYS_TO_PFN((start+end) != PHYS_TO_PFN(start)) should be
> safe in all cases?

Just move away from discontigmem completely.  Sparsemem can do everything
we need on ARM at a lesser cost.  As I say above, discontigmem is really
for NUMA platforms, and ARM is not a NUMA platform.  No one on ARM should
be going anywhere near discontigmem.