On 1/28/21 8:33 AM, Zi Yan wrote: >> One of the many lasting (as we don't coalesce back) sources for >> huge page splits is tracing as the granular page >> attribute/permission changes would force the kernel to split code >> segments mapped to huge pages to smaller ones thereby increasing >> the probability of TLB miss/reload even after tracing has been >> stopped. > It is interesting to see this statement saying splitting kernel > direct mappings causes performance loss, when Zhengjun (cc’d) from > Intel recently posted a kernel direct mapping performance report[1] > saying 1GB mappings are good but not much better than 2MB and 4KB > mappings. No, that's not what the report said. *Overall*, there is no clear winner between 4k, 2M and 1G. In other words, no one page size is best for *ALL* workloads. There were *ABSOLUTELY* individual workloads in those tests that saw significant deltas between the direct map sizes. There are also real-world workloads that feel the impact here.
