On Mon, 25 Apr 2022 20:23:56 +0530 Aneesh Kumar K V <aneesh.kumar@xxxxxxxxxxxxx> wrote: > On 4/25/22 7:27 PM, Jonathan Cameron wrote: > > On Mon, 25 Apr 2022 16:45:38 +0530 > > Jagdish Gediya <jvgediya@xxxxxxxxxxxxx> wrote: > > > > .... > > >> $ 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. > > > > I'm not convinced the distinction between DRAM and persistent memory is > > valid. There will definitely be systems with a large pool > > of remote DRAM (and potentially no NV memory) where the right choice > > is to demote to that DRAM pool. > > > > Basing the decision on whether the memory is from kmem or > > normal DRAM doesn't provide sufficient information to make the decision. > > > >> > >> $ 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 > >> > >> 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 > > > > I'd argue that is wrong. At this state you have a tiered memory system > > be it one with just DRAM. Using it as such is correct behavior that > > we should not be preventing. Sure some usecases wouldn't want that > > arrangement but some do want it. > > > > I missed this in my earlier reply. Are you suggesting that we would want > Node 1 (DRAM only memory numa node) to act as demotion target for Node > 0? Any reason why we would want to do that? That is clearly opposite of > what we are trying to do here. IMHO node using Node1 as demotion target > for Node0 is a better default? In this case, because of the small size that probably wouldn't make sense. But, if that were a CXL memory pool with multiple TB of DDR then yes we would want the default case to use that memory for the demotion path. So I don't think DDR vs NV via kmem alone is the right basis for a decision on the default behavior. Sure we can make this all a userspace problem. Jonathan > > > > -aneesh
