linux-kernel - Re: [ofa-general] Re: Demand paging for memory regions

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Date:	Thu, 14 Feb 2008 10:23:23 -0600
From:	Steve Wise <swise@...ngridcomputing.com>
To:	Robin Holt <holt@....com>
CC:	Felix Marti <felix@...lsio.com>, Roland Dreier <rdreier@...co.com>,
	Christoph Lameter <clameter@....com>,
	Rik van Riel <riel@...hat.com>, steiner@....com,
	Andrea Arcangeli <andrea@...ranet.com>, a.p.zijlstra@...llo.nl,
	izike@...ranet.com, linux-kernel@...r.kernel.org, avi@...ranet.com,
	linux-mm@...ck.org, daniel.blueman@...drics.com,
	general@...ts.openfabrics.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	kvm-devel@...ts.sourceforge.net
Subject: Re: [ofa-general] Re: Demand paging for memory regions

Robin Holt wrote:
> On Thu, Feb 14, 2008 at 09:09:08AM -0600, Steve Wise wrote:
>> Note that for T3, this involves suspending _all_ rdma connections that are 
>> in the same PD as the MR being remapped.  This is because the driver 
>> doesn't know who the application advertised the rkey/stag to.  So without 
> 
> Is there a reason the driver can not track these.
> 

Because advertising of a MR (ie telling the peer about your rkey/stag, 
offset and length) is application-specific and can be done out of band, 
or in band as simple SEND/RECV payload. Either way, the driver has no 
way of tracking this because the protocol used is application-specific.

>> Point being, it will stop probably all connections that an application is 
>> using (assuming the application uses a single PD).
> 
> It seems like the need to not stop all would be a compelling enough reason
> to modify the driver to track which processes have received the rkey/stag.
> 

Yes, _if_ the driver could track this.

And _if_ the rdma API and paradigm was such that the kernel/driver could 
keep track, then remote revokations of MR tags could be supported.

Stevo
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