Messages in this thread | | | Subject | Re: [PATCH v3 0/6] percpu: partial chunk depopulation | From | Pratik Sampat <> | Date | Sat, 17 Apr 2021 12:44:24 +0530 |
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On 17/04/21 3:17 am, Dennis Zhou wrote: > Hello, > > 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 >> >> Pasting the full logs as an example: >> >> BEFORE >> Percpu Memory Statistics >> Allocation Info: >> ---------------------------------------- >> unit_size : 655360 >> static_size : 608920 >> reserved_size : 0 >> dyn_size : 46440 >> atom_size : 65536 >> alloc_size : 655360 >> >> Global Stats: >> ---------------------------------------- >> nr_alloc : 9038 >> nr_dealloc : 6992 >> nr_cur_alloc : 2046 >> nr_max_alloc : 2200 >> nr_chunks : 3 >> nr_max_chunks : 3 >> min_alloc_size : 4 >> max_alloc_size : 1072 >> empty_pop_pages : 12 >> >> Per Chunk Stats: >> ---------------------------------------- >> Chunk: <- First Chunk >> nr_alloc : 1092 >> max_alloc_size : 1072 >> empty_pop_pages : 0 >> first_bit : 16247 >> free_bytes : 4 >> contig_bytes : 4 >> sum_frag : 4 >> max_frag : 4 >> cur_min_alloc : 4 >> cur_med_alloc : 8 >> cur_max_alloc : 1072 >> memcg_aware : 0 >> >> Chunk: >> nr_alloc : 594 >> max_alloc_size : 992 >> empty_pop_pages : 8 >> first_bit : 456 >> free_bytes : 645008 >> contig_bytes : 319984 >> sum_frag : 325024 >> max_frag : 318680 >> cur_min_alloc : 4 >> cur_med_alloc : 8 >> cur_max_alloc : 424 >> memcg_aware : 0 >> >> Chunk: >> nr_alloc : 360 >> max_alloc_size : 1072 >> empty_pop_pages : 4 >> first_bit : 26595 >> free_bytes : 506640 >> contig_bytes : 506540 >> sum_frag : 100 >> max_frag : 32 >> cur_min_alloc : 4 >> cur_med_alloc : 156 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> >> AFTER >> Percpu Memory Statistics >> Allocation Info: >> ---------------------------------------- >> unit_size : 655360 >> static_size : 608920 >> reserved_size : 0 >> dyn_size : 46440 >> atom_size : 65536 >> alloc_size : 655360 >> >> Global Stats: >> ---------------------------------------- >> nr_alloc : 97046 >> nr_dealloc : 94304 >> nr_cur_alloc : 2742 >> nr_max_alloc : 90054 >> nr_chunks : 11 >> nr_max_chunks : 47 >> min_alloc_size : 4 >> max_alloc_size : 1072 >> empty_pop_pages : 18 >> >> Per Chunk Stats: >> ---------------------------------------- >> Chunk: <- First Chunk >> nr_alloc : 1092 >> max_alloc_size : 1072 >> empty_pop_pages : 0 >> first_bit : 16247 >> free_bytes : 4 >> contig_bytes : 4 >> sum_frag : 4 >> max_frag : 4 >> cur_min_alloc : 4 >> cur_med_alloc : 8 >> cur_max_alloc : 1072 >> memcg_aware : 0 >> >> Chunk: >> nr_alloc : 838 >> max_alloc_size : 1072 >> empty_pop_pages : 7 >> first_bit : 464 >> free_bytes : 640476 >> contig_bytes : 290672 >> sum_frag : 349804 >> max_frag : 304344 >> cur_min_alloc : 4 >> cur_med_alloc : 8 >> cur_max_alloc : 1072 >> memcg_aware : 0 >> >> Chunk: >> nr_alloc : 90 >> max_alloc_size : 1072 >> empty_pop_pages : 0 >> first_bit : 536 >> free_bytes : 595752 >> contig_bytes : 26164 >> sum_frag : 575132 >> max_frag : 26164 >> cur_min_alloc : 156 >> cur_med_alloc : 1072 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> Chunk: >> nr_alloc : 90 >> max_alloc_size : 1072 >> empty_pop_pages : 0 >> first_bit : 0 >> free_bytes : 597428 >> contig_bytes : 26164 >> sum_frag : 596848 >> max_frag : 26164 >> cur_min_alloc : 156 >> cur_med_alloc : 312 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> Chunk: >> nr_alloc : 92 >> max_alloc_size : 1072 >> empty_pop_pages : 0 >> first_bit : 0 >> free_bytes : 595284 >> contig_bytes : 26164 >> sum_frag : 590360 >> max_frag : 26164 >> cur_min_alloc : 156 >> cur_med_alloc : 312 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> Chunk: >> nr_alloc : 92 >> max_alloc_size : 1072 >> empty_pop_pages : 0 >> first_bit : 0 >> free_bytes : 595284 >> contig_bytes : 26164 >> sum_frag : 583768 >> max_frag : 26164 >> cur_min_alloc : 156 >> cur_med_alloc : 312 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> Chunk: >> nr_alloc : 360 >> max_alloc_size : 1072 >> empty_pop_pages : 7 >> first_bit : 26595 >> free_bytes : 506640 >> contig_bytes : 506540 >> sum_frag : 100 >> max_frag : 32 >> cur_min_alloc : 4 >> cur_med_alloc : 156 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> Chunk: >> nr_alloc : 12 >> max_alloc_size : 1072 >> empty_pop_pages : 3 >> first_bit : 0 >> free_bytes : 647524 >> contig_bytes : 563492 >> sum_frag : 57872 >> max_frag : 26164 >> cur_min_alloc : 156 >> cur_med_alloc : 312 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> Chunk: >> nr_alloc : 0 >> max_alloc_size : 1072 >> empty_pop_pages : 1 >> first_bit : 0 >> free_bytes : 655360 >> contig_bytes : 655360 >> sum_frag : 0 >> max_frag : 0 >> cur_min_alloc : 0 >> cur_med_alloc : 0 >> cur_max_alloc : 0 >> memcg_aware : 1 >> >> Chunk (sidelined): >> nr_alloc : 72 >> max_alloc_size : 1072 >> empty_pop_pages : 0 >> first_bit : 0 >> free_bytes : 608344 >> contig_bytes : 145552 >> sum_frag : 590340 >> max_frag : 145552 >> cur_min_alloc : 156 >> cur_med_alloc : 312 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> Chunk (sidelined): >> nr_alloc : 4 >> max_alloc_size : 1072 >> empty_pop_pages : 0 >> first_bit : 0 >> free_bytes : 652748 >> contig_bytes : 426720 >> sum_frag : 426720 >> max_frag : 426720 >> cur_min_alloc : 156 >> cur_med_alloc : 312 >> cur_max_alloc : 1072 >> memcg_aware : 1 >> >> > > Thank you Pratik for testing this and working with us to resolve this. I > greatly appreciate it! > > Thanks, > Dennis
No worries at all, glad I could be of some help!
Thank you, Pratik
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