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From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
To: Roland Dreier <rdreier@cisco.com>
Cc: Christoph Lameter <clameter@sgi.com>,
	Rik van Riel <riel@redhat.com>,
	steiner@sgi.com, Andrea Arcangeli <andrea@qumranet.com>,
	a.p.zijlstra@chello.nl, izike@qumranet.com,
	linux-kernel@vger.kernel.org, avi@qumranet.com,
	linux-mm@kvack.org, daniel.blueman@quadrics.com,
	Robin Holt <holt@sgi.com>,
	general@lists.openfabrics.org,
	Andrew Morton <akpm@linux-foundation.org>,
	kvm-devel@lists.sourceforge.net
Subject: Re: [ofa-general] Re: Demand paging for memory regions
Date: Tue, 12 Feb 2008 16:23:29 -0700	[thread overview]
Message-ID: <20080212232329.GC31435@obsidianresearch.com> (raw)
In-Reply-To: <adazlu5vlub.fsf@cisco.com>

On Tue, Feb 12, 2008 at 02:41:48PM -0800, Roland Dreier wrote:
>  > > Chelsio's T3 HW doesn't support this.
> 
>  > Not so far I guess but it could be equipped with these features right? 
> 
> I don't know anything about the T3 internals, but it's not clear that
> you could do this without a new chip design in general.  Lot's of RDMA
> devices were designed expecting that when a packet arrives, the HW can
> look up the bus address for a given memory region/offset and place
> the

Well, certainly today the memfree IB devices store the page tables in
host memory so they are already designed to hang onto packets during
the page lookup over PCIE, adding in faulting makes this time
larger.

But this is not a good thing at all, IB's congestion model is based on
the notion that end ports can always accept packets without making
input contigent on output. If you take a software interrupt to fill in
the page pointer then you could potentially deadlock on the
fabric. For example using this mechanism to allow swap-in of RDMA target
pages and then putting the storage over IB would be deadlock
prone. Even without deadlock slowing down the input path will cause
network congestion and poor performance for other nodes. It is not a
desirable thing to do..

I expect that iwarp running over flow controlled ethernet has similar
kinds of problems for similar reasons..

In general the best I think you can hope for with RDMA hardware is
page migration using some atomic operations with the adaptor and a cpu
page copy with retry sort of scheme - but is pure page migration
interesting at all?

Jason

  parent reply	other threads:[~2008-02-12 23:52 UTC|newest]

Thread overview: 81+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-08 22:06 [patch 0/6] MMU Notifiers V6 Christoph Lameter
2008-02-08 22:06 ` [patch 1/6] mmu_notifier: Core code Christoph Lameter
2008-02-08 22:06 ` [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges Christoph Lameter
2008-02-08 22:06 ` [patch 3/6] mmu_notifier: invalidate_page callbacks Christoph Lameter
2008-02-08 22:06 ` [patch 4/6] mmu_notifier: Skeleton driver for a simple mmu_notifier Christoph Lameter
2008-02-08 22:06 ` [patch 5/6] mmu_notifier: Support for drivers with revers maps (f.e. for XPmem) Christoph Lameter
2008-02-08 22:06 ` [patch 6/6] mmu_rmap_notifier: Skeleton for complex driver that uses its own rmaps Christoph Lameter
2008-02-08 22:23 ` [patch 0/6] MMU Notifiers V6 Andrew Morton
2008-02-08 23:32   ` Christoph Lameter
2008-02-08 23:36     ` Robin Holt
2008-02-08 23:41       ` Christoph Lameter
2008-02-08 23:43         ` Robin Holt
2008-02-08 23:56           ` Andrew Morton
2008-02-09  0:05             ` Christoph Lameter
2008-02-09  0:12               ` [ofa-general] " Roland Dreier
2008-02-09  0:16                 ` Christoph Lameter
2008-02-09  0:22                   ` Roland Dreier
2008-02-09  0:36                     ` Christoph Lameter
2008-02-09  1:24                       ` Andrea Arcangeli
2008-02-09  1:27                         ` Christoph Lameter
2008-02-09  1:56                           ` Andrea Arcangeli
2008-02-09  2:16                             ` Christoph Lameter
2008-02-09 12:55                               ` Rik van Riel
2008-02-09 21:46                                 ` Christoph Lameter
2008-02-11 22:40                                   ` Demand paging for memory regions (was Re: MMU Notifiers V6) Roland Dreier
2008-02-12 22:01                                     ` Steve Wise
2008-02-12 22:10                                       ` Christoph Lameter
2008-02-12 22:41                                         ` [ofa-general] Re: Demand paging for memory regions Roland Dreier
2008-02-12 23:14                                           ` Felix Marti
2008-02-13  0:57                                             ` Christoph Lameter
2008-02-14 15:09                                             ` Steve Wise
2008-02-14 15:53                                               ` Robin Holt
2008-02-14 16:23                                                 ` Steve Wise
2008-02-14 17:48                                                   ` Caitlin Bestler
2008-02-14 19:39                                               ` Christoph Lameter
2008-02-14 20:17                                                 ` Caitlin Bestler
2008-02-14 20:20                                                   ` Christoph Lameter
2008-02-14 22:43                                                     ` Caitlin Bestler
2008-02-14 22:48                                                       ` Christoph Lameter
2008-02-15  1:26                                                         ` Caitlin Bestler
2008-02-15  2:37                                                           ` Christoph Lameter
2008-02-15 18:09                                                             ` Caitlin Bestler
2008-02-15 18:45                                                               ` Christoph Lameter
2008-02-15 18:53                                                                 ` Caitlin Bestler
2008-02-15 20:02                                                                   ` Christoph Lameter
2008-02-15 20:14                                                                     ` Caitlin Bestler
2008-02-15 22:50                                                                       ` Christoph Lameter
2008-02-15 23:50                                                                         ` Caitlin Bestler
2008-02-12 23:23                                           ` Jason Gunthorpe [this message]
2008-02-13  1:01                                             ` Christoph Lameter
2008-02-13  1:26                                               ` Jason Gunthorpe
2008-02-13  1:45                                                 ` Steve Wise
2008-02-13  2:35                                                 ` Christoph Lameter
2008-02-13  3:25                                                   ` Jason Gunthorpe
2008-02-13  3:56                                                     ` Patrick Geoffray
2008-02-13  4:26                                                       ` Jason Gunthorpe
2008-02-13  4:47                                                         ` Patrick Geoffray
2008-02-13 18:51                                                     ` Christoph Lameter
2008-02-13 19:51                                                       ` Jason Gunthorpe
2008-02-13 20:36                                                         ` Christoph Lameter
2008-02-13  4:09                                                   ` Christian Bell
2008-02-13 19:00                                                     ` Christoph Lameter
2008-02-13 19:46                                                       ` Christian Bell
2008-02-13 20:32                                                         ` Christoph Lameter
2008-02-13 22:44                                                           ` Kanoj Sarcar
2008-02-13 23:02                                                             ` Christoph Lameter
2008-02-13 23:43                                                               ` Kanoj Sarcar
2008-02-13 23:48                                                                 ` Jesse Barnes
2008-02-14  0:56                                                                 ` [ofa-general] " Andrea Arcangeli
2008-02-14 19:35                                                                 ` Christoph Lameter
2008-02-13 23:23                                                     ` Pete Wyckoff
2008-02-14  0:01                                                       ` Jason Gunthorpe
2008-02-27 22:11                                                         ` Christoph Lameter
2008-02-13  1:55                                               ` Christian Bell
2008-02-13  2:19                                                 ` Christoph Lameter
2008-02-13  0:56                                           ` Christoph Lameter
2008-02-13 12:11                                           ` Christoph Raisch
2008-02-13 19:02                                             ` Christoph Lameter
2008-02-09  0:12               ` [patch 0/6] MMU Notifiers V6 Andrew Morton
2008-02-09  0:18                 ` Christoph Lameter
2008-02-13 14:31 ` Jack Steiner

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