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. > > > Chris > > On Wed, Nov 8, 2023 at 6:10 PM Chris Li <chrisl@xxxxxxxxxx> wrote: > > > > On Wed, Nov 8, 2023 at 4:28 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > > > > > Hmm my guess is that I probably sent this out based on an outdated > > > mm-unstable. There has since been a new zswap selftest merged > > > to mm-unstable (written by no other than myself - oh the irony), so > > > maybe it does not apply cleanly anymore with git am. > > > > $ git am -3 patches/zswap-pool-lru/0005 > > Applying: selftests: cgroup: update per-memcg zswap writeback selftest > > Using index info to reconstruct a base tree... > > M tools/testing/selftests/cgroup/test_zswap.c > > Falling back to patching base and 3-way merge... > > Auto-merging tools/testing/selftests/cgroup/test_zswap.c > > $ git am -3 patches/zswap-pool-lru/0006 > > Applying: zswap: shrinks zswap pool based on memory pressure > > error: sha1 information is lacking or useless (mm/zswap.c). > > error: could not build fake ancestor > > Patch failed at 0001 zswap: shrinks zswap pool based on memory pressure > > hint: Use 'git am --show-current-patch=diff' to see the failed patch > > When you have resolved this problem, run "git am --continue". > > If you prefer to skip this patch, run "git am --skip" instead. > > To restore the original branch and stop patching, run "git am --abort". > > > > I was able to resolve the conflict on patch 6 by hand though. So I am good now. > > > > Thanks > > > > Chris
