Messages in this thread | | | Date | Wed, 1 May 2019 14:43:36 +0800 | From | Fengguang Wu <> | Subject | Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node |
| |
On Wed, Apr 17, 2019 at 11:17:48AM +0200, Michal Hocko wrote: >On Tue 16-04-19 12:19:21, Yang Shi wrote: >> >> >> On 4/16/19 12:47 AM, Michal Hocko wrote: >[...] >> > Why cannot we simply demote in the proximity order? Why do you make >> > cpuless nodes so special? If other close nodes are vacant then just use >> > them. >> >> We could. But, this raises another question, would we prefer to just demote >> to the next fallback node (just try once), if it is contended, then just >> swap (i.e. DRAM0 -> PMEM0 -> Swap); or 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)? > >I would go with the later. Why, because it is more natural. Because that >is the natural allocation path so I do not see why this shouldn't be the >natural demotion path.
"Demotion" should be more performance wise by "demoting to the next-level (cheaper/slower) memory". Otherwise something like this may happen.
DRAM0 pressured => demote cold pages to DRAM1 DRAM1 pressured => demote cold pages to DRAM0
Kind of DRAM0/DRAM1 exchanged a fraction of the demoted cold pages, which looks not helpful for overall system performance.
Over time, it's even possible some cold pages get "demoted" in path DRAM0=>DRAM1=>DRAM0=>DRAM1=>...
Thanks, Fengguang
| |