Light summary of LPC discussions on io page table

Can these people please raise their voice here? Or maybe LPC's IOMMU discussions were summarized somewhere in an email sent to the IOMMU ML, where we could discuss that, instead of this thread.

Quoted 3 lines · Boris Brezillon

Can these people please raise their voice here? Or maybe LPC's IOMMU discussions were summarized somewhere in an email sent to the IOMMU ML, where we could discuss that, instead of this thread.

I think we are using session recordings mostly these days? I have a bunch of people interested - I'm going to work to launch another group project to tackle this. Maybe in Jan.

The recordings are not broken up yet, but here is the master:

https://www.youtube.com/live/vO2mAM8wOvU

Pasha's talk is first at 2:21, and there was some discussion in the room that may be hard to hear including the use of RCU and the refcount. Pasha is interested in solving the memory waste his VFIO application causes which is basically an algorithmic problem inside the io page table. There was also some side discussion about optimizations. mm implements a batch free technique that could apply here too, and a batch alloc is also potentially interesting.

My talk starts at 3:11 and we have another discussion later around this issue in the context of dirty tracking optimization. Joao has written and shared some code for what is concerning there in an earlier email Sean C is the voice at the back sharing the KVM learnings that getting to a common implementation is highly recommended

I had an interesting hallway discussion about a use case for bringing back the old VFIO type 1.0 huge page split behavior and implementing it in every enterprise iommu.

Then we have this DRM need, which I've come to think of as a guarenteed map without a table level allocate.

These need touching all the "enterprise" focused page table formats. There are so many now, doing the algorithm work 5-7 times is not reasonable. A common radix algorithm and a more complex shared implementation relying on RCU is the direction I want to head in. mm shows a template how to achieve this, and I have some rough ideas to explore.