Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes: > On 3/29/2022 10:04 PM, Jagdish Gediya wrote: >> On Tue, Mar 29, 2022 at 08:26:05PM +0800, Baolin Wang wrote: >> Hi Baolin, >>> Hi Jagdish, >>> >>> On 3/29/2022 7:52 PM, Jagdish Gediya wrote: >>>> The current implementation to identify the demotion >>>> targets limits some of the opportunities to share >>>> the demotion targets between multiple source nodes. >>>> >>>> Implement a logic to identify the loop in the demotion >>>> targets such that all the possibilities of demotion can >>>> be utilized. Don't share the used targets between all >>>> the nodes, instead create the used targets from scratch >>>> for each individual node based on for what all node this >>>> node is a demotion target. This helps to share the demotion >>>> targets without missing any possible way of demotion. >>>> >>>> e.g. with below NUMA topology, where node 0 & 1 are >>>> cpu + dram nodes, node 2 & 3 are equally slower memory >>>> only nodes, and node 4 is slowest memory only node, >>>> >>>> available: 5 nodes (0-4) >>>> node 0 cpus: 0 1 >>>> node 0 size: n MB >>>> node 0 free: n MB >>>> node 1 cpus: 2 3 >>>> node 1 size: n MB >>>> node 1 free: n MB >>>> node 2 cpus: >>>> node 2 size: n MB >>>> node 2 free: n MB >>>> node 3 cpus: >>>> node 3 size: n MB >>>> node 3 free: n MB >>>> node 4 cpus: >>>> node 4 size: n MB >>>> node 4 free: n MB >>>> node distances: >>>> node 0 1 2 3 4 >>>> 0: 10 20 40 40 80 >>>> 1: 20 10 40 40 80 >>>> 2: 40 40 10 40 80 >>>> 3: 40 40 40 10 80 >>>> 4: 80 80 80 80 10 >>>> >>>> The existing implementation gives below demotion targets, >>>> >>>> node demotion_target >>>> 0 3, 2 >>>> 1 4 >>>> 2 X >>>> 3 X >>>> 4 X >>>> >>>> With this patch applied, below are the demotion targets, >>>> >>>> node demotion_target >>>> 0 3, 2 >>>> 1 3, 2 >>>> 2 3 >>>> 3 4 >>>> 4 X >>> >>> Node 2 and node 3 both are slow memory and have same distance, why node 2 >>> should demote cold memory to node 3? They should have the same target >>> demotion node 4, which is the slowest memory node, right? >>> >> Current demotion target finding algorithm works based on best distance, as distance between node 2 & 3 is 40 and distance between node 2 & 4 is 80, node 2 demotes to node 3. > > If node 2 can demote to node 3, which means node 3's memory is colder > than node 2, right? The accessing time of node 3 should be larger than > node 2, then we can demote colder memory to node 3 from node 2. > > But node 2 and node 3 are same memory type and have same distance, the > accessing time of node 2 and node 3 should be same too, so why add so > many page migration between node 2 and node 3? I'm still not sure the > benefits. > > Huang Ying and Dave, how do you think about this demotion targets? Yes. I think the demotion target of 2 should be 4, as in my another email in this thread. Demoting from 2 to 3 makes no sense. Best Regards, Huang, Ying [snip]
