On 4/14/21 9:07 PM, Wei Xu wrote: > On Wed, Apr 14, 2021 at 1:08 AM Oscar Salvador <osalva...@suse.de> wrote: >> Fast class/memory are pictured as those nodes with CPUs, while Slow >> class/memory >> are PMEM, right? >> Then, what stands for medium class/memory? > > That is Dave's example. I think David's guess makes sense (HBM - fast, DRAM - > medium, PMEM - slow). It may also be possible that we have DDR5 as fast, > CXL-DDR4 as medium, and CXL-PMEM as slow. But the most likely use cases for > now should be just two tiers: DRAM vs PMEM or other types of slower > memory devices.
Yes, it would be nice to apply this to fancier tiering systems. But DRAM/PMEM combos are out in the wild today and it's where I expect this to be used first. > This can help enable more flexible demotion policies to be > configured, such as to allow a cgroup to allocate from all fast tier > nodes, but only demote to a local slow tier node. Such a policy can > reduce memory stranding at the fast tier (compared to if memory > hardwall is used) and still allow demotion from all fast tier nodes > without incurring the expensive random accesses to the demoted pages > if they were demoted to remote slow tier nodes. Could you explain this stranding effect in a bit more detail? I'm not quite following.
