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From: Pratik Sampat <psampat@linux.ibm.com>
To: Dennis Zhou <dennis@kernel.org>
Cc: Roman Gushchin <guro@fb.com>, Tejun Heo <tj@kernel.org>,
	Christoph Lameter <cl@linux.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	pratik.r.sampat@gmail.com
Subject: Re: [PATCH v3 0/6] percpu: partial chunk depopulation
Date: Sat, 17 Apr 2021 12:44:24 +0530	[thread overview]
Message-ID: <3b6724dd-e345-c730-ad18-492cfd6af885@linux.ibm.com> (raw)
In-Reply-To: <YHoF+XfC8Ul2/KPj@google.com>



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


  reply	other threads:[~2021-04-17  7:14 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-08  3:57 Roman Gushchin
2021-04-08  3:57 ` [PATCH v3 1/6] percpu: fix a comment about the chunks ordering Roman Gushchin
2021-04-16 21:06   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 2/6] percpu: split __pcpu_balance_workfn() Roman Gushchin
2021-04-16 21:06   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 3/6] percpu: make pcpu_nr_empty_pop_pages per chunk type Roman Gushchin
2021-04-16 21:08   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 4/6] percpu: generalize pcpu_balance_populated() Roman Gushchin
2021-04-16 21:09   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 5/6] percpu: factor out pcpu_check_chunk_hint() Roman Gushchin
2021-04-16 21:15   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 6/6] percpu: implement partial chunk depopulation Roman Gushchin
2021-04-16 12:56 ` [PATCH v3 0/6] percpu: " Pratik Sampat
2021-04-16 14:18   ` Dennis Zhou
2021-04-16 15:28     ` Pratik Sampat
2021-04-16 17:13       ` Roman Gushchin
2021-04-16 18:27         ` Pratik Sampat
2021-04-16 18:34           ` Roman Gushchin
2021-04-16 18:41             ` Pratik Sampat
2021-04-16 19:09               ` Roman Gushchin
2021-04-16 19:44                 ` Pratik Sampat
2021-04-16 20:03                   ` Roman Gushchin
2021-04-17  7:08                     ` Pratik Sampat
2021-04-16 21:47                   ` Dennis Zhou
2021-04-17  7:14                     ` Pratik Sampat [this message]
2021-04-16 16:21     ` Roman Gushchin

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