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Message-ID: <2a0d371d-79f6-e7aa-6dcd-3b29264e1feb@linux.ibm.com>
Date: Sat, 17 Apr 2021 01:14:03 +0530
From: Pratik Sampat <psampat@...ux.ibm.com>
To: Roman Gushchin <guro@...com>
Cc: Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
Christoph Lameter <cl@...ux.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, pratik.r.sampat@...il.com
Subject: Re: [PATCH v3 0/6] percpu: partial chunk depopulation
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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