120b51af1SHuang YingWhat: /sys/kernel/mm/numa/ 220b51af1SHuang YingDate: June 2021 320b51af1SHuang YingContact: Linux memory management mailing list <linux-mm@kvack.org> 420b51af1SHuang YingDescription: Interface for NUMA 520b51af1SHuang Ying 620b51af1SHuang YingWhat: /sys/kernel/mm/numa/demotion_enabled 720b51af1SHuang YingDate: June 2021 820b51af1SHuang YingContact: Linux memory management mailing list <linux-mm@kvack.org> 920b51af1SHuang YingDescription: Enable/disable demoting pages during reclaim 1020b51af1SHuang Ying 1120b51af1SHuang Ying Page migration during reclaim is intended for systems 1220b51af1SHuang Ying with tiered memory configurations. These systems have 1320b51af1SHuang Ying multiple types of memory with varied performance 1420b51af1SHuang Ying characteristics instead of plain NUMA systems where 1520b51af1SHuang Ying the same kind of memory is found at varied distances. 1620b51af1SHuang Ying Allowing page migration during reclaim enables these 1720b51af1SHuang Ying systems to migrate pages from fast tiers to slow tiers 1820b51af1SHuang Ying when the fast tier is under pressure. This migration 19*7d709f49SGregory Price is performed before swap if an eligible numa node is 20*7d709f49SGregory Price present in cpuset.mems for the cgroup (or if cpuset v1 21*7d709f49SGregory Price is being used). If cpusets.mems changes at runtime, it 22*7d709f49SGregory Price may move data to a NUMA node that does not fall into the 23*7d709f49SGregory Price cpuset of the new cpusets.mems, which might be construed 24*7d709f49SGregory Price to violate the guarantees of cpusets. Shared memory, 25*7d709f49SGregory Price such as libraries, owned by another cgroup may still be 26*7d709f49SGregory Price demoted and result in memory use on a node not present 27*7d709f49SGregory Price in cpusets.mem. This should not be enabled on systems 28*7d709f49SGregory Price which need strict cpuset location guarantees. 29