Messages in this thread | | | Subject | Re: [PATCH v3 0/6] percpu: partial chunk depopulation | From | Pratik Sampat <> | Date | Sat, 17 Apr 2021 01:14:03 +0530 |
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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
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