linux-kernel - Re: [PATCH]IB/ehca:reject dynamic memory add/remove

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Message-Id: <1223987353.29877.40.camel@nimitz>
Date:	Tue, 14 Oct 2008 05:29:13 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Stefan Roscher <stefan.roscher@...t.de.ibm.com>
Cc:	Stefan Roscher <ossrosch@...ux.vnet.ibm.com>,
	Roland Dreier <rolandd@...co.com>,
	general@...ts.openfabrics.org,
	LinuxPPC-Dev <linuxppc-dev@...abs.org>,
	LKML <linux-kernel@...r.kernel.org>, hnguyen@...ibm.com
Subject: Re: [PATCH]IB/ehca:reject dynamic memory add/remove

On Tue, 2008-10-14 at 14:23 +0200, Stefan Roscher wrote:
> On Monday 13 October 2008 07:09:26 pm Dave Hansen wrote:
> > On Mon, 2008-10-13 at 13:10 +0200, Stefan Roscher wrote:
> > > Since the ehca device driver does not support dynamic memory add and remove
> > > operations, the driver must explicitly reject such requests in order to prevent
> > > unpredictable behaviors related to memory regions already occupied and being
> > > used by InfiniBand applications.
> > > The solution is to add a memory notifier to the ehca device driver and if a request
> > > for dynamic memory add or remove comes in, ehca will always reject it.
> > 
> > Why doesn't the driver support it?
> > 
> > This seems like an awfully extreme action to take.  Do you have plans to
> > support this in the driver soon?
> > 
> There is currently a slight incompatibility how openfabrics uses MRs
> and how System p does DMEM add/remove, which basically disables this
> support.
> If you want to talk to the firmware developpers, I can give you the right contacts.

I wish I knew what an 'MR' is. :(

Could you be a bit more specific so we can get a better changelog?
Perhaps if we understand the situation better, we can come up with a
better solution.

Does this have anything in common with the problems with 16GB pages?

-- Dave

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