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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000439, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/23/2025 11:25 AM, Shivank Garg wrote: > Hi all, > > Zi Yan and I would like to propose the topic: Enhancements to Page > Migration with Multi-threading and Batch Offloading to DMA. > > Page migration is a critical operation in NUMA systems that can incur > significant overheads, affecting memory management performance across > various workloads. For example, copying folios between DRAM NUMA nodes > can take ~25% of the total migration cost for migrating 256MB of data. > > Modern systems are equipped with powerful DMA engines for bulk data > copying, GPUs, and high CPU core counts. Leveraging these hardware > capabilities becomes essential for systems where frequent page promotion > and demotion occur - from large-scale tiered-memory systems with CXL nodes > to CPU-GPU coherent system with GPU memory exposed as NUMA nodes. > > Existing page migration performs sequential page copying, underutilizing > modern CPU architectures and high-bandwidth memory subsystems. > > We have proposed and posted RFCs to enhance page migration through three > key techniques: > 1. Batching migration operations for bulk copying data [1] > 2. Multi-threaded folio copying [2] > 3. DMA offloading to hardware accelerators [1] > > By employing batching and multi-threaded folio copying, we are able to > achieve significant improvements in page migration throughput for large > pages. > > Discussion points: > 1. Performance: > a. Policy decision for DMA and CPU selection > b. Platform-specific scheduling of folio-copy worker threads for better > bandwidth utilization > c. Using Non-temporal instructions for CPU-based memcpy > d. Upscaling/downscaling worker threads based on migration size, CPU > availability (system load), bandwidth saturation, etc. > 2. Interface requirements with DMA hardware: > a. Standardizing APIs for DMA drivers and support for different DMA > drivers > b. Enhancing DMA drivers for bulk copying (e.g., SDXi Engine) > 3. Resources Accounting: > a. CPU cgroups accounting and fairness [3] > b. Who bears migration cost? - (Migration cost attribution) > Hi all, For reference, here is the link to the latest RFC v2: https://lore.kernel.org/linux-mm/20250319192211.10092-1-shivankg@amd.com This version combines the ideas discussed in [1] and [2] and includes details on performance improvements and experimental findings to provide more context for discussion. > References: > [1] https://lore.kernel.org/all/20240614221525.19170-1-shivankg@amd.com > [2] https://lore.kernel.org/all/20250103172419.4148674-1-ziy@nvidia.com > [3] https://lore.kernel.org/all/CAHbLzkpoKP0fVZP5b10wdzAMDLWysDy7oH0qaUssiUXj80R6bw@mail.gmail.com Looking forward to your feedback! Thanks, Shivank