On Tue 23-08-22 09:21:16, Suren Baghdasaryan wrote: > On Tue, Aug 23, 2022 at 4:51 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Tue 23-08-22 17:20:59, Zhaoyang Huang wrote: > > > On Tue, Aug 23, 2022 at 4:33 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > > > On Tue 23-08-22 14:03:04, Zhaoyang Huang wrote: > > > > > On Tue, Aug 23, 2022 at 1:21 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > > > > > > > On Tue 23-08-22 10:31:57, Zhaoyang Huang wrote: > > > > [...] > > > > > > > I would like to quote the comments from google side for more details > > > > > > > which can also be observed from different vendors. > > > > > > > "Also be advised that when you enable memcg v2 you will be using > > > > > > > per-app memcg configuration which implies noticeable overhead because > > > > > > > every app will have its own group. For example pagefault path will > > > > > > > regress by about 15%. And obviously there will be some memory overhead > > > > > > > as well. That's the reason we don't enable them in Android by > > > > > > > default." > > > > > > > > > > > > This should be reported and investigated. Because per-application memcg > > > > > > vs. memcg in general shouldn't make much of a difference from the > > > > > > performance side. I can see a potential performance impact for no-memcg > > > > > > vs. memcg case but even then 15% is quite a lot. > > > > > Less efficiency on memory reclaim caused by multi-LRU should be one of > > > > > the reason, which has been proved by comparing per-app memcg on/off. > > > > > Besides, theoretically workingset could also broken as LRU is too > > > > > short to compose workingset. > > > > > > > > Do you have any data to back these claims? Is this something that could > > > > be handled on the configuration level? E.g. by applying low limit > > > > protection to keep the workingset in the memory? > > > I don't think so. IMO, workingset works when there are pages evicted > > > from LRU and then refault which provide refault distance for pages. > > > Applying memcg's protection will have all LRU out of evicted which > > > make the mechanism fail. > > > > It is really hard to help you out without any actual data. The idea was > > though to use the low limit protection to adaptively configure > > respective memcgs to reduce refaults. You already have data about > > refaults ready so increasing the limit for often refaulting memcgs would > > reduce the trashing. > > Sorry for joining late. > A couple years ago I tested root-memcg vs per-app memcg configurations > on an Android phone. Here is a snapshot from my findings: > > Problem > ======= > We see tangible increase in major faults and workingset refaults when > transitioning from root-only memory cgroup to per-application cgroups > on Android. > > Test results > ============ > Results while running memory-demanding workload: > root memcg per-app memcg delta > workingset_refault 1771228 3874281 +118.73% > workingset_nodereclaim 4543 13928 +206.58% > pgpgin 13319208 20618944 +54.81% > pgpgout 1739552 3080664 +77.1% > pgpgoutclean 2616571 4805755 +83.67% > pswpin 359211 3918716 +990.92% > pswpout 1082238 5697463 +426.45% > pgfree 28978393 32531010 +12.26% > pgactivate 2586562 8731113 +237.56% > pgdeactivate 3811074 11670051 +206.21% > pgfault 38692510 46096963 +19.14% > pgmajfault 441288 4100020 +829.1% > pgrefill 4590451 12768165 +178.15% > > Results while running application cycle test (20 apps, 20 cycles): > root memcg per-app memcg delta > workingset_refault 10634691 11429223 +7.47% > workingset_nodereclaim 37477 59033 +57.52% > pgpgin 70662840 69569516 -1.55% > pgpgout 2605968 2695596 +3.44% > pgpgoutclean 13514955 14980610 +10.84% > pswpin 1489851 3780868 +153.77% > pswpout 4125547 8050819 +95.15% > pgfree 99823083 105104637 +5.29% > pgactivate 7685275 11647913 +51.56% > pgdeactivate 14193660 21459784 +51.19% > pgfault 89173166 100598528 +12.81% > pgmajfault 1856172 4227190 +127.74% > pgrefill 16643554 23203927 +39.42% Thanks! It would be interesting to see per memcg stats as well. Are there any outliers? Are there any signs of over-reclaim (more pages scanned & reclaimed by both kswapd and direct reclaim? > Tests were conducted on an Android phone with 4GB RAM. > Similar regression was reported a couple years ago here: > https://www.spinics.net/lists/linux-mm/msg121665.html > > I plan on checking the difference again on newer kernels (likely 5.15) > after LPC this September. Thanks, that would be useful! -- Michal Hocko SUSE Labs
