On Sat, Apr 17, 2021 at 01:14:03AM +0530, Pratik Sampat wrote: > > > On 17/04/21 12:39 am, Roman Gushchin wrote: > > On Sat, Apr 17, 2021 at 12:11:37AM +0530, Pratik Sampat wrote: > > > > > > On 17/04/21 12:04 am, Roman Gushchin wrote: > > > > On Fri, Apr 16, 2021 at 11:57:03PM +0530, Pratik Sampat wrote: > > > > > On 16/04/21 10:43 pm, Roman Gushchin wrote: > > > > > > On Fri, Apr 16, 2021 at 08:58:33PM +0530, Pratik Sampat wrote: > > > > > > > Hello Dennis, > > > > > > > > > > > > > > I apologize for the clutter of logs before, I'm pasting the logs > > > > > > > of before and > > > > > > > after the percpu test in the case of the patchset being applied > > > > > > > on 5.12-rc6 and > > > > > > > the vanilla kernel 5.12-rc6. > > > > > > > > > > > > > > On 16/04/21 7:48 pm, Dennis Zhou wrote: > > > > > > > > Hello, > > > > > > > > > > > > > > > > On Fri, Apr 16, 2021 at 06:26:15PM +0530, Pratik Sampat wrote: > > > > > > > > > Hello Roman, > > > > > > > > > > > > > > > > > > I've tried the v3 patch series on a POWER9 and an x86 KVM > > > > > > > > > setup. > > > > > > > > > > > > > > > > > > My results of the percpu_test are as follows: > > > > > > > > > Intel KVM 4CPU:4G > > > > > > > > > Vanilla 5.12-rc6 > > > > > > > > > # ./percpu_test.sh > > > > > > > > > Percpu: 1952 kB > > > > > > > > > Percpu: 219648 kB > > > > > > > > > Percpu: 219648 kB > > > > > > > > > > > > > > > > > > 5.12-rc6 + with patchset applied > > > > > > > > > # ./percpu_test.sh > > > > > > > > > Percpu: 2080 kB > > > > > > > > > Percpu: 219712 kB > > > > > > > > > Percpu: 72672 kB > > > > > > > > > > > > > > > > > > I'm able to see improvement comparable to that of what you're > > > > > > > > > see too. > > > > > > > > > > > > > > > > > > However, on POWERPC I'm unable to reproduce these > > > > > > > > > improvements with the patchset in the same configuration > > > > > > > > > > > > > > > > > > POWER9 KVM 4CPU:4G > > > > > > > > > Vanilla 5.12-rc6 > > > > > > > > > # ./percpu_test.sh > > > > > > > > > Percpu: 5888 kB > > > > > > > > > Percpu: 118272 kB > > > > > > > > > Percpu: 118272 kB > > > > > > > > > > > > > > > > > > 5.12-rc6 + with patchset applied > > > > > > > > > # ./percpu_test.sh > > > > > > > > > Percpu: 6144 kB > > > > > > > > > Percpu: 119040 kB > > > > > > > > > Percpu: 119040 kB > > > > > > > > > > > > > > > > > > I'm wondering if there's any architectural specific code that > > > > > > > > > needs plumbing > > > > > > > > > here? > > > > > > > > > > > > > > > > > There shouldn't be. Can you send me the percpu_stats debug > > > > > > > > output before > > > > > > > > and after? > > > > > > > I'll paste the whole debug stats before and after here. > > > > > > > 5.12-rc6 + patchset > > > > > > > -----BEFORE----- > > > > > > > Percpu Memory Statistics > > > > > > > Allocation Info: > > > > > > Hm, this looks highly suspicious. Here is your stats in a more > > > > > > compact form: > > > > > > > > > > > > Vanilla > > > > > > > > > > > > nr_alloc : 9038 nr_alloc : > > > > > > 97046 > > > > > > nr_dealloc : 6992 nr_dealloc : > > > > > > 94237 > > > > > > nr_cur_alloc : 2046 nr_cur_alloc : > > > > > > 2809 > > > > > > nr_max_alloc : 2178 nr_max_alloc : > > > > > > 90054 > > > > > > nr_chunks : 3 nr_chunks : > > > > > > 11 > > > > > > nr_max_chunks : 3 nr_max_chunks : > > > > > > 47 > > > > > > min_alloc_size : 4 min_alloc_size : > > > > > > 4 > > > > > > max_alloc_size : 1072 max_alloc_size : > > > > > > 1072 > > > > > > empty_pop_pages : 5 empty_pop_pages : > > > > > > 29 > > > > > > > > > > > > > > > > > > Patched > > > > > > > > > > > > nr_alloc : 9040 nr_alloc : > > > > > > 97048 > > > > > > nr_dealloc : 6994 nr_dealloc : > > > > > > 95002 > > > > > > nr_cur_alloc : 2046 nr_cur_alloc : > > > > > > 2046 > > > > > > nr_max_alloc : 2208 nr_max_alloc : > > > > > > 90054 > > > > > > nr_chunks : 3 nr_chunks : > > > > > > 48 > > > > > > nr_max_chunks : 3 nr_max_chunks : > > > > > > 48 > > > > > > min_alloc_size : 4 min_alloc_size : > > > > > > 4 > > > > > > max_alloc_size : 1072 max_alloc_size : > > > > > > 1072 > > > > > > empty_pop_pages : 12 empty_pop_pages : > > > > > > 61 > > > > > > > > > > > > > > > > > > So it looks like the number of chunks got bigger, as well as the > > > > > > number of > > > > > > empty_pop_pages? This contradicts to what you wrote, so can you, > > > > > > please, make > > > > > > sure that the data is correct and we're not messing two cases? > > > > > > > > > > > > So it looks like for some reason sidelined (depopulated) chunks are > > > > > > not getting > > > > > > freed completely. But I struggle to explain why the initial > > > > > > empty_pop_pages is > > > > > > bigger with the same amount of chunks. > > > > > > > > > > > > So, can you, please, apply the following patch and provide an > > > > > > updated statistics? > > > > > Unfortunately, I'm not completely well versed in this area, but yes > > > > > the empty > > > > > pop pages number doesn't make sense to me either. > > > > > > > > > > I re-ran the numbers trying to make sure my experiment setup is sane > > > > > but > > > > > results remain the same. > > > > > > > > > > Vanilla > > > > > nr_alloc : 9040 nr_alloc : > > > > > 97048 > > > > > nr_dealloc : 6994 nr_dealloc : > > > > > 94404 > > > > > nr_cur_alloc : 2046 nr_cur_alloc : > > > > > 2644 > > > > > nr_max_alloc : 2169 nr_max_alloc : > > > > > 90054 > > > > > nr_chunks : 3 nr_chunks : > > > > > 10 > > > > > nr_max_chunks : 3 nr_max_chunks : > > > > > 47 > > > > > min_alloc_size : 4 min_alloc_size : > > > > > 4 > > > > > max_alloc_size : 1072 max_alloc_size : > > > > > 1072 > > > > > empty_pop_pages : 4 empty_pop_pages : > > > > > 32 > > > > > > > > > > With the patchset + debug patch the results are as follows: > > > > > Patched > > > > > > > > > > nr_alloc : 9040 nr_alloc : > > > > > 97048 > > > > > nr_dealloc : 6994 nr_dealloc : > > > > > 94349 > > > > > nr_cur_alloc : 2046 nr_cur_alloc : > > > > > 2699 > > > > > nr_max_alloc : 2194 nr_max_alloc : > > > > > 90054 > > > > > nr_chunks : 3 nr_chunks : > > > > > 48 > > > > > nr_max_chunks : 3 nr_max_chunks : > > > > > 48 > > > > > min_alloc_size : 4 min_alloc_size : > > > > > 4 > > > > > max_alloc_size : 1072 max_alloc_size : > > > > > 1072 > > > > > empty_pop_pages : 12 empty_pop_pages : > > > > > 54 > > > > > > > > > > With the extra tracing I can see 39 entries of "Chunk (sidelined)" > > > > > after the test was run. I don't see any entries for "Chunk (to > > > > > depopulate)" > > > > > > > > > > I've snipped the results of slidelined chunks because they went on > > > > > for ~600 > > > > > lines, if you need the full logs let me know. > > > > Yes, please! That's the most interesting part! > > > Got it. Pasting the full logs of after the percpu experiment was completed > > Thanks! > > > > Would you mind to apply the following patch and test again? > > > > -- > > > > diff --git a/mm/percpu.c b/mm/percpu.c > > index ded3a7541cb2..532c6a7ebdfd 100644 > > --- a/mm/percpu.c > > +++ b/mm/percpu.c > > @@ -2296,6 +2296,9 @@ void free_percpu(void __percpu *ptr) > > need_balance = true; > > break; > > } > > + > > + chunk->depopulated = false; > > + pcpu_chunk_relocate(chunk, -1); > > } else if (chunk != pcpu_first_chunk && chunk != > > pcpu_reserved_chunk && > > !chunk->isolated && > > (pcpu_nr_empty_pop_pages[pcpu_chunk_type(chunk)] > > > > Sure thing. > > I see much lower sideline chunks. In one such test run I saw zero occurrences > of slidelined chunks > So looking at the stats it now works properly. Do you see any savings in comparison to vanilla? The size of savings can significanlty depend on the exact size of cgroup-related objects, how many of them fit into a single chunk, etc. So you might want to play with numbers in the test...
Anyway, thank you very much for the report and your work on testing follow-up patches! It helped to reveal a serious bug in the implementation (completely empty sidelined chunks were not released in some cases), which by pure coincidence wasn't triggered on x86. Thanks!
