linux-kernel - Re: Interacting with coherent memory on external devices

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Date:	Fri, 24 Apr 2015 22:32:33 -0400
From:	Rik van Riel <riel@...hat.com>
To:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
CC:	jglisse@...hat.com, mgorman@...e.de, aarcange@...hat.com,
	airlied@...hat.com, benh@...nel.crashing.org,
	aneesh.kumar@...ux.vnet.ibm.com,
	Cameron Buschardt <cabuschardt@...dia.com>,
	Mark Hairgrove <mhairgrove@...dia.com>,
	Geoffrey Gerfin <ggerfin@...dia.com>,
	John McKenna <jmckenna@...dia.com>, akpm@...ux-foundation.org
Subject: Re: Interacting with coherent memory on external devices

On 04/21/2015 05:44 PM, Paul E. McKenney wrote:

> AUTONUMA
> 
> 	The Linux kernel's autonuma facility supports migrating both
> 	memory and processes to promote NUMA memory locality.  It was
> 	accepted into 3.13 and is available in RHEL 7.0 and SLES 12.
> 	It is enabled by the Kconfig variable CONFIG_NUMA_BALANCING.
> 
> 	This approach uses a kernel thread "knuma_scand" that periodically
> 	marks pages inaccessible.  The page-fault handler notes any
> 	mismatches between the NUMA node that the process is running on
> 	and the NUMA node on which the page resides.

Minor nit: marking pages inaccessible is done from task_work
nowadays, there no longer is a kernel thread.

> 	The result would be that the kernel would allocate only migratable
> 	pages within the CCAD device's memory, and even then only if
> 	memory was otherwise exhausted.

Does it make sense to allocate the device's page tables in memory
belonging to the device?

Is this a necessary thing with some devices? Jerome's HMM comes
to mind...

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