On Wed 02-11-22 16:02:54, Huang, Ying wrote: > Michal Hocko <mhocko@xxxxxxxx> writes: > > > On Wed 02-11-22 08:39:49, Huang, Ying wrote: > >> Michal Hocko <mhocko@xxxxxxxx> writes: > >> > >> > On Mon 31-10-22 09:33:49, Huang, Ying wrote: > >> > [...] > >> >> In the upstream implementation, 4 tiers are possible below DRAM. That's > >> >> enough for now. But in the long run, it may be better to define more. > >> >> 100 possible tiers below DRAM may be too extreme. > >> > > >> > I am just curious. Is any configurations with more than couple of tiers > >> > even manageable? I mean applications have been struggling even with > >> > regular NUMA systems for years and vast majority of them is largerly > >> > NUMA unaware. How are they going to configure for a more complex system > >> > when a) there is no resource access control so whatever you aim for > >> > might not be available and b) in which situations there is going to be a > >> > demand only for subset of tears (GPU memory?) ? > >> > >> Sorry for confusing. I think that there are only several (less than 10) > >> tiers in a system in practice. Yes, here, I suggested to define 100 (10 > >> in the later text) POSSIBLE tiers below DRAM. My intention isn't to > >> manage a system with tens memory tiers. Instead, my intention is to > >> avoid to put 2 memory types into one memory tier by accident via make > >> the abstract distance range of each memory tier as small as possible. > >> More possible memory tiers, smaller abstract distance range of each > >> memory tier. > > > > TBH I do not really understand how tweaking ranges helps anything. > > IIUC drivers are free to assign any abstract distance so they will clash > > without any higher level coordination. > > Yes. That's possible. Each memory tier corresponds to one abstract > distance range. The larger the range is, the higher the possibility of > clashing is. So I suggest to make the abstract distance range smaller > to reduce the possibility of clashing. I am sorry but I really do not understand how the size of the range actually addresses a fundamental issue that each driver simply picks what it wants. Is there any enumeration defining basic characteristic of each tier? How does a driver developer knows which tear to assign its driver to? -- Michal Hocko SUSE Labs
