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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: Fri, 16 Apr 2021 20:58:33 +0530	[thread overview]
Message-ID: <7a001bf6-5708-fb04-4970-367d9845ccb9@linux.ibm.com> (raw)
In-Reply-To: <YHmcorqNE5NpAN3G@google.com>

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:
----------------------------------------
   unit_size           :       655360
   static_size         :       608920
   reserved_size       :            0
   dyn_size            :        46440
   atom_size           :        65536
   alloc_size          :       655360

Global Stats:
----------------------------------------
   nr_alloc            :         9040
   nr_dealloc          :         6994
   nr_cur_alloc        :         2046
   nr_max_alloc        :         2208
   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            :          859
   max_alloc_size      :         1072
   empty_pop_pages     :            0
   first_bit           :        16384
   free_bytes          :            0
   contig_bytes        :            0
   sum_frag            :            0
   max_frag            :            0
   cur_min_alloc       :            4
   cur_med_alloc       :            8
   cur_max_alloc       :         1072
   memcg_aware         :            0

Chunk:
   nr_alloc            :          827
   max_alloc_size      :          992
   empty_pop_pages     :            8
   first_bit           :          692
   free_bytes          :       645012
   contig_bytes        :       460096
   sum_frag            :       466420
   max_frag            :       460096
   cur_min_alloc       :            4
   cur_med_alloc       :            8
   cur_max_alloc       :          152
   memcg_aware         :            0

Chunk:
   nr_alloc            :          360
   max_alloc_size      :         1072
   empty_pop_pages     :            4
   first_bit           :        29207
   free_bytes          :       506640
   contig_bytes        :       506556
   sum_frag            :           84
   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            :        97048
   nr_dealloc          :        95002
   nr_cur_alloc        :         2046
   nr_max_alloc        :        90054
   nr_chunks           :           48
   nr_max_chunks       :           48
   min_alloc_size      :            4
   max_alloc_size      :         1072
   empty_pop_pages     :           61

Per Chunk Stats:
----------------------------------------
Chunk: <- First Chunk
   nr_alloc            :          859
   max_alloc_size      :         1072
   empty_pop_pages     :            0
   first_bit           :        16384
   free_bytes          :            0
   contig_bytes        :            0
   sum_frag            :            0
   max_frag            :            0
   cur_min_alloc       :            4
   cur_med_alloc       :            8
   cur_max_alloc       :         1072
   memcg_aware         :            0

Chunk:
   nr_alloc            :          827
   max_alloc_size      :         1072
   empty_pop_pages     :            8
   first_bit           :          692
   free_bytes          :       645012
   contig_bytes        :       460096
   sum_frag            :       466420
   max_frag            :       460096
   cur_min_alloc       :            4
   cur_med_alloc       :            8
   cur_max_alloc       :          152
   memcg_aware         :            0

Chunk:
   nr_alloc            :            0
   max_alloc_size      :            0
   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         :            0

Chunk:
   nr_alloc            :          360
   max_alloc_size      :         1072
   empty_pop_pages     :            7
   first_bit           :        29207
   free_bytes          :       506640
   contig_bytes        :       506556
   sum_frag            :           84
   max_frag            :           32
   cur_min_alloc       :            4
   cur_med_alloc       :          156
   cur_max_alloc       :         1072
   memcg_aware         :            1

Chunk:
   nr_alloc            :            0
   max_alloc_size      :         1072
   empty_pop_pages     :            0
   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


I'm also pasting the logs before and after in a vanilla kernel too
There are considerably higher number of chunks in the vanilla kernel, than with
the patches though.

5.12-rc6 vanilla
-----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        :         2178
   nr_chunks           :            3
   nr_max_chunks       :            3
   min_alloc_size      :            4
   max_alloc_size      :         1072
   empty_pop_pages     :            5

Per Chunk Stats:
----------------------------------------
Chunk: <- First Chunk
   nr_alloc            :         1088
   max_alloc_size      :         1072
   empty_pop_pages     :            0
   first_bit           :        16384
   free_bytes          :            0
   contig_bytes        :            0
   sum_frag            :            0
   max_frag            :            0
   cur_min_alloc       :            4
   cur_med_alloc       :            8
   cur_max_alloc       :         1072
   memcg_aware         :            0

Chunk:
   nr_alloc            :          598
   max_alloc_size      :          992
   empty_pop_pages     :            5
   first_bit           :          642
   free_bytes          :       645012
   contig_bytes        :       504292
   sum_frag            :       140720
   max_frag            :       116456
   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     :            0
   first_bit           :        27909
   free_bytes          :       506640
   contig_bytes        :       506556
   sum_frag            :           84
   max_frag            :           36
   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          :        94237
   nr_cur_alloc        :         2809
   nr_max_alloc        :        90054
   nr_chunks           :           11
   nr_max_chunks       :           47
   min_alloc_size      :            4
   max_alloc_size      :         1072
   empty_pop_pages     :           29

Per Chunk Stats:
----------------------------------------
Chunk: <- First Chunk
   nr_alloc            :         1088
   max_alloc_size      :         1072
   empty_pop_pages     :            0
   first_bit           :        16384
   free_bytes          :            0
   contig_bytes        :            0
   sum_frag            :            0
   max_frag            :            0
   cur_min_alloc       :            4
   cur_med_alloc       :            8
   cur_max_alloc       :         1072
   memcg_aware         :            0

Chunk:
   nr_alloc            :          865
   max_alloc_size      :         1072
   empty_pop_pages     :            6
   first_bit           :          789
   free_bytes          :       640296
   contig_bytes        :       290672
   sum_frag            :       349624
   max_frag            :       169956
   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            :           90
   max_alloc_size      :         1072
   empty_pop_pages     :            0
   first_bit           :            0
   free_bytes          :       595752
   contig_bytes        :        26164
   sum_frag            :       577748
   max_frag            :        26164
   cur_min_alloc       :          156
   cur_med_alloc       :         1072
   cur_max_alloc       :         1072
   memcg_aware         :            1

Chunk:
   nr_alloc            :           30
   max_alloc_size      :         1072
   empty_pop_pages     :            6
   first_bit           :            0
   free_bytes          :       636608
   contig_bytes        :       397944
   sum_frag            :       636500
   max_frag            :       426720
   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           :        27909
   free_bytes          :       506640
   contig_bytes        :       506556
   sum_frag            :           84
   max_frag            :           36
   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     :            0
   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     :           10
   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

>> I will also look through the code to find the reason why POWER isn't
>> depopulating pages.
>>
>> Thank you,
>> Pratik
>>
>> On 08/04/21 9:27 am, Roman Gushchin wrote:
>>> In our production experience the percpu memory allocator is sometimes struggling
>>> with returning the memory to the system. A typical example is a creation of
>>> several thousands memory cgroups (each has several chunks of the percpu data
>>> used for vmstats, vmevents, ref counters etc). Deletion and complete releasing
>>> of these cgroups doesn't always lead to a shrinkage of the percpu memory,
>>> so that sometimes there are several GB's of memory wasted.
>>>
>>> The underlying problem is the fragmentation: to release an underlying chunk
>>> all percpu allocations should be released first. The percpu allocator tends
>>> to top up chunks to improve the utilization. It means new small-ish allocations
>>> (e.g. percpu ref counters) are placed onto almost filled old-ish chunks,
>>> effectively pinning them in memory.
>>>
>>> This patchset solves this problem by implementing a partial depopulation
>>> of percpu chunks: chunks with many empty pages are being asynchronously
>>> depopulated and the pages are returned to the system.
>>>
>>> To illustrate the problem the following script can be used:
>>>
>>> --
>>> #!/bin/bash
>>>
>>> cd /sys/fs/cgroup
>>>
>>> mkdir percpu_test
>>> echo "+memory" > percpu_test/cgroup.subtree_control
>>>
>>> cat /proc/meminfo | grep Percpu
>>>
>>> for i in `seq 1 1000`; do
>>>       mkdir percpu_test/cg_"${i}"
>>>       for j in `seq 1 10`; do
>>> 	mkdir percpu_test/cg_"${i}"_"${j}"
>>>       done
>>> done
>>>
>>> cat /proc/meminfo | grep Percpu
>>>
>>> for i in `seq 1 1000`; do
>>>       for j in `seq 1 10`; do
>>> 	rmdir percpu_test/cg_"${i}"_"${j}"
>>>       done
>>> done
>>>
>>> sleep 10
>>>
>>> cat /proc/meminfo | grep Percpu
>>>
>>> for i in `seq 1 1000`; do
>>>       rmdir percpu_test/cg_"${i}"
>>> done
>>>
>>> rmdir percpu_test
>>> --
>>>
>>> It creates 11000 memory cgroups and removes every 10 out of 11.
>>> It prints the initial size of the percpu memory, the size after
>>> creating all cgroups and the size after deleting most of them.
>>>
>>> Results:
>>>     vanilla:
>>>       ./percpu_test.sh
>>>       Percpu:             7488 kB
>>>       Percpu:           481152 kB
>>>       Percpu:           481152 kB
>>>
>>>     with this patchset applied:
>>>       ./percpu_test.sh
>>>       Percpu:             7488 kB
>>>       Percpu:           481408 kB
>>>       Percpu:           135552 kB
>>>
>>> So the total size of the percpu memory was reduced by more than 3.5 times.
>>>
>>> v3:
>>>     - introduced pcpu_check_chunk_hint()
>>>     - fixed a bug related to the hint check
>>>     - minor cosmetic changes
>>>     - s/pretends/fixes (cc Vlastimil)
>>>
>>> v2:
>>>     - depopulated chunks are sidelined
>>>     - depopulation happens in the reverse order
>>>     - depopulate list made per-chunk type
>>>     - better results due to better heuristics
>>>
>>> v1:
>>>     - depopulation heuristics changed and optimized
>>>     - chunks are put into a separate list, depopulation scan this list
>>>     - chunk->isolated is introduced, chunk->depopulate is dropped
>>>     - rearranged patches a bit
>>>     - fixed a panic discovered by krobot
>>>     - made pcpu_nr_empty_pop_pages per chunk type
>>>     - minor fixes
>>>
>>> rfc:
>>>     https://lwn.net/Articles/850508/
>>>
>>>
>>> Roman Gushchin (6):
>>>     percpu: fix a comment about the chunks ordering
>>>     percpu: split __pcpu_balance_workfn()
>>>     percpu: make pcpu_nr_empty_pop_pages per chunk type
>>>     percpu: generalize pcpu_balance_populated()
>>>     percpu: factor out pcpu_check_chunk_hint()
>>>     percpu: implement partial chunk depopulation
>>>
>>>    mm/percpu-internal.h |   4 +-
>>>    mm/percpu-stats.c    |   9 +-
>>>    mm/percpu.c          | 306 +++++++++++++++++++++++++++++++++++--------
>>>    3 files changed, 261 insertions(+), 58 deletions(-)
>>>
> Roman, sorry for the delay. I'm looking to apply this today to for-5.14.
>
> Thanks,
> Dennis
Thanks
Pratik

  reply	other threads:[~2021-04-16 15:29 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 [this message]
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
2021-04-16 16:21     ` Roman Gushchin

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