linux-kernel - Re: [PATCH] drivers/base: export gpl (un)register_memory

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Message-Id: <1203010575.12312.6.camel@dyn9047017100.beaverton.ibm.com>
Date:	Thu, 14 Feb 2008 09:36:15 -0800
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	Christoph Raisch <RAISCH@...ibm.com>, ossthema@...ux.vnet.ibm.com,
	apw <apw@...ibm.com>, Greg KH <greg@...ah.com>,
	Jan-Bernd Themann <THEMANN@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...abs.org, netdev <netdev@...r.kernel.org>,
	Thomas Q Klein <TKLEIN@...ibm.com>, tklein@...ux.ibm.com
Subject: Re: [PATCH] drivers/base: export gpl (un)register_memory_notifier

On Thu, 2008-02-14 at 09:12 -0800, Dave Hansen wrote:
..
> > > > - Use currently other not exported functions in kernel/resource.c, like
> > > >   walk_memory_resource (where we would still need the maximum
> > > possible number
> > > >   of pages NR_MEM_SECTIONS)
> > >
> > > It isn't the act of exporting that's the problem.  It's making sure that
> > > the exports won't be prone to abuse and that people are using them
> > > properly.  You should assume that you can export and use
> > > walk_memory_resource().
> > 
> > So this seems to come down to a basic question:
> > New hardware seems to have a tendency to get "private MMUs",
> > which need private mappings from the kernel address space into a
> > "HW defined address space with potentially unique characteristics"
> > RDMA in Openfabrics with global MR is the most prominent example heading
> > there
> 
> That's not a question. ;)
> 
> Please explain to me why walk_memory_resource() is insufficient for your
> needs.  I've now pointed it out to you at least 3 times.  

I am not sure what you are trying to do with walk_memory_resource(). The
behavior is different on ppc64. Hotplug memory usage assumes that all
the memory resources (all system memory, not just IOMEM) are represented
in /proc/iomem. Its the case with i386 and ia64. But on ppc64 is
contains ONLY iomem related. Paulus didn't want to export all the system
memory into /proc/iomem on ppc64. So I had to workaround by providing
arch-specific walk_memory_resource() function for ppc64.

Thanks,
Badari

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