On Tue 16-04-19 14:22:33, Dave Hansen wrote: > On 4/16/19 12:19 PM, Yang Shi wrote: > > would we prefer to try all the nodes in the fallback order to find the > > first less contended one (i.e. DRAM0 -> PMEM0 -> DRAM1 -> PMEM1 -> Swap)? > > Once a page went to DRAM1, how would we tell that it originated in DRAM0 > and is following the DRAM0 path rather than the DRAM1 path? > > Memory on DRAM0's path would be: > > DRAM0 -> PMEM0 -> DRAM1 -> PMEM1 -> Swap > > Memory on DRAM1's path would be: > > DRAM1 -> PMEM1 -> DRAM0 -> PMEM0 -> Swap > > Keith Busch had a set of patches to let you specify the demotion order > via sysfs for fun. The rules we came up with were: I am not a fan of any sysfs "fun" > 1. Pages keep no history of where they have been makes sense > 2. Each node can only demote to one other node Not really, see my other email. I do not really see any strong reason why not use the full zonelist to demote to > 3. The demotion path can not have cycles yes. This could be achieved by GFP_NOWAIT opportunistic allocation for the migration target. That should prevent from loops or artificial nodes exhausting quite naturaly AFAICS. Maybe we will need some tricks to raise the watermark but I am not convinced something like that is really necessary. -- Michal Hocko SUSE Labs
