On Tue, 7 May 2024, Michal Hocko wrote: > On Mon 06-05-24 20:37:19, David Rientjes wrote: > > Hi all, > > > > I think it would be very worthwhile to have a block set aside for > > discussion on locally attached memory tiering extensions at LSF/MM/BPF > > 2024. > > > > Primarily interested in discussing Linux enlightenment for CXL 1.1 and > > later type-3 memory expansion devices (CXL.mem). I think we could touch > > on CXL 2.0 and later memory pooling architectures if we have time and > > there is interest, but the primary focus here would be local attached. > > > > Based on the premise for a Memory Tiering Working Group[1], there is > > widespread interest in the foundational topics for generally useful Linux > > enlightenment: > > > > - Decoupling CPU balancing from memory balancing (or obsoleting CPU > > balancing entirely) > > > > + John Hubbard notes this would be useful for GPUs: > > > > a) GPUs have their own processors that are invisible to the kernel's > > NUMA "which tasks are active on which NUMA nodes" calculations, > > and > > > > b) Similar to where CXL is generally going, we have already built > > fully memory-coherent hardware, which include memory-only NUMA > > nodes. > > > > - In-kernel hot memory abstraction, informed by hardware hinting drivers > > (incl some architectures like Power10), usable as a NUMA Balancing > > backend for promotion and other areas of the kernel like transparent > > hugepage utilization > > > > - NUMA and memory tiering enlightenment for accelerators, such as for > > optimal use of GPU memory, extremely important for a cloud provider > > (hint hint :) > > > > - Asynchronous memory promotion independent of task_numa_fault() while > > considering the cost of page migration (due to identifying cold memory) > > > > - What the role of userspace plays in this decision-making and how we can > > extend the default policy and mechanisms in the kernel to allow for it > > if necessary > > > > Additional topics that you find interesting are also very helpful! > > > > I'm biased toward a generally useful solution that would leverage the > > kernel as the ultimate source of truth for page hotness that can be > > extended for multiple use caes, one of which is memory tiering support. > > But certainly if there are other approaches, we can discuss that as well. > > > > A few main goals from this discussion: > > > > - Ensure that proposals address, or can be extended to address, the > > emerging needs of the various use cases that users may have > > > > - Surface any constraints that stakeholders may find to be prohibitive > > for support in the core MM subsystem > > > > - Alignment and division of work for developers who are actively looking > > to contribute to this area > > Do you think having 2 contigious slots would be sufficient for these > topics? > Yes, I think that makes perfect sense. > > As I'm just one of many stakeholders for this discussion, I'd nominate > > Michal Hocko to moderate it if he's willing to do so. > > Sure I can help out with that. > Thank you Michal! All: if there are additional topics that we discuss in this block beyond what is listed above, that would be great feedback. We can make sure that it is all covered in session, so please expand upon the above for things that we should cover. Thanks!
