Re: [PATCH v6 5/6] nouveau: use new mmu interval notifiers
From: Ralph Campbell
Date: Wed Feb 19 2020 - 20:10:54 EST
On 1/16/20 12:21 PM, Jason Gunthorpe wrote:
On Thu, Jan 16, 2020 at 12:16:30PM -0800, Ralph Campbell wrote:
Thanks for the information, Jason.
Can you point me to the latest ODP code? Seems like my understanding is
Look for the word 'implicit'
mlx5_ib_invalidate_range() releases the interval_notifier when there are
no populated shadow PTEs in its leaf
pagefault_implicit_mr() creates an interval_notifier that covers the
level in the page table that needs population. Notice it just uses an
unlocked xa_load to find the page table level.
The locking is pretty tricky as it relies on RCU, but the fault flow
is fairly lightweight.
I'm still interested in finding a way to support range based hints to device drivers.
madvise() looks like it only sets a bit in vma->vm_flags or acts on the
advice immediately. mbind() and set_mempolicy() only work with CPUs and memory
with NUMA a node number. What I'm looking for is a way for the device to know
whether to migrate pages to device private memory on a fault, whether to duplicate
read-only pages in device private memory, or remote map/access a page instead of migrating it.
For example, there is a working draft extension to OpenCL,
that could provide a way to specify this sort of advice.
C++ is also looking at extentions for specifying affinity attributes.
In any case, these are probably a long ways off before being finalized and implemented.
I also have some changes to support THP migration to device private memory but that
will require updating nouveau to use 2MB TLB mappings.
In the mean time, I can update the HMM self tests to do something like ODP without
changing mm/mmu_notifier.c but I don't think I can easily change nouveau to that model.