On Fri, Nov 17, 2023 at 8:23 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > On Thu, Nov 16, 2023 at 4:57 PM Chris Li <chrisl@xxxxxxxxxx> wrote: > > > > Hi Nhat, > > > > I want want to share the high level feedback we discussed here in the > > mailing list as well. > > > > It is my observation that each memcg LRU list can't compare the page > > time order with other memcg. > > It works great when the leaf level memcg hits the memory limit and you > > want to reclaim from that memcg. > > It works less well on the global memory pressure you need to reclaim > > from all memcg. You kind of have to > > scan each all child memcg to find out the best page to shrink from. It > > is less effective to get to the most desirable page quickly. > > > > This can benefit from a design similar to MGLRU. This idea is > > suggested by Yu Zhao, credit goes to him not me. > > In other words, the current patch is similar to the memcg page list > > pre MGLRU world. We can have a MRLRU > > like per memcg zswap shrink list. > > I was gonna summarize the points myself :P But thanks for doing this. > It's your idea so you're more qualified to explain this anyway ;) > > I absolutely agree that having a generation-aware cgroup-aware > NUMA-aware LRU is the future way to go. Currently, IIUC, the reclaim logic > selects cgroups in a round-robin-ish manner. It's "fair" in this perspective, > but I also think it's not ideal. As we have discussed, the current list_lru > infrastructure only take into account intra-cgroup relative recency, not > inter-cgroup relative recency. The recently proposed time-based zswap > reclaim mechanism will provide us with a source of information, but the > overhead of using this might be too high - and it's very zswap-specific. > > Maybe after this, we should improve zswap reclaim (and perhaps all > list_lru users) by adding generations to list_lru then take generations > into account in the vmscan code. This patch series could be merged > as-is, and once we make list_lru generation-aware, zswap shrinker > will automagically be improved (along with all other list_lru/shrinker > users). > > I don't know enough about the current design of MGLRU to comment > too much further, but let me know if this makes sense, and if you have > objections/other ideas. > > And if you have other documentations for MGLRU than its code, could > you please let me know? I'm struggling to find more details about this. > This could be a good place to start: https://www.youtube.com/watch?v=9HvJfN21H9Y
