Re: Interacting with coherent memory on external devices

From: Rik van Riel
Date: Fri Apr 24 2015 - 22:33:32 EST

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

> 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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