On Mon, 2022-04-25 at 16:45 +0530, Jagdish Gediya wrote: > On Sun, Apr 24, 2022 at 11:19:53AM +0800, ying.huang@xxxxxxxxx wrote: > > On Sat, 2022-04-23 at 01:25 +0530, Jagdish Gediya wrote: > > > Some systems(e.g. PowerVM) can have both DRAM(fast memory) only > > > NUMA node which are N_MEMORY and slow memory(persistent memory) > > > only NUMA node which are also N_MEMORY. As the current demotion > > > target finding algorithm works based on N_MEMORY and best distance, > > > it will choose DRAM only NUMA node as demotion target instead of > > > persistent memory node on such systems. If DRAM only NUMA node is > > > filled with demoted pages then at some point new allocations can > > > start falling to persistent memory, so basically cold pages are in > > > fast memor (due to demotion) and new pages are in slow memory, this > > > is why persistent memory nodes should be utilized for demotion and > > > dram node should be avoided for demotion so that they can be used > > > for new allocations. > > > > > > Current implementation can work fine on the system where the memory > > > only numa nodes are possible only for persistent/slow memory but it > > > is not suitable for the like of systems mentioned above. > > > > Can you share the NUMA topology information of your machine? And the > > demotion order before and after your change? > > > > Whether it's good to use the PMEM nodes as the demotion targets of the > > DRAM-only node too? > > $ numactl -H > available: 2 nodes (0-1) > node 0 cpus: 0 1 2 3 4 5 6 7 > node 0 size: 14272 MB > node 0 free: 13392 MB > node 1 cpus: > node 1 size: 2028 MB > node 1 free: 1971 MB > node distances: > node 0 1 > 0: 10 40 > 1: 40 10 > > 1) without N_DEMOTION_TARGETS patch series, 1 is demotion target > for 0 even when 1 is DRAM node and there is no demotion targets for 1. > > $ cat /sys/bus/nd/devices/dax0.0/target_node > 2 > $ > # cd /sys/bus/dax/drivers/ > :/sys/bus/dax/drivers# ls > device_dax kmem > :/sys/bus/dax/drivers# cd device_dax/ > :/sys/bus/dax/drivers/device_dax# echo dax0.0 > unbind > :/sys/bus/dax/drivers/device_dax# echo dax0.0 > ../kmem/new_id > :/sys/bus/dax/drivers/device_dax# numactl -H > available: 3 nodes (0-2) > node 0 cpus: 0 1 2 3 4 5 6 7 > node 0 size: 14272 MB > node 0 free: 13380 MB > node 1 cpus: > node 1 size: 2028 MB > node 1 free: 1961 MB > node 2 cpus: > node 2 size: 0 MB > node 2 free: 0 MB > node distances: > node 0 1 2 > 0: 10 40 80 > 1: 40 10 80 > 2: 80 80 10 > This looks like a virtual machine, not a real machine. That's unfortunate. I am looking forward to a real issue, not a theoritical possible issue. > 2) Once this new node brought online, without N_DEMOTION_TARGETS > patch series, 1 is demotion target for 0 and 2 is demotion target > for 1. > > With this patch series applied, > 1) No demotion target for either 0 or 1 before dax device is online > 2) 2 is demotion target for both 0 and 1 after dax device is online. > So with your change, if a node hasn't N_DEMOTION_TARGETS, it will become a top-level demotion source even if it hasn't N_CPU? If so, I cannot clear N_DEMOTION_TARGETS for a node in middle or bottom level? Best Regards, Huang, Ying > > [snip]
