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Message-ID: <7a001bf6-5708-fb04-4970-367d9845ccb9@linux.ibm.com>
Date: Fri, 16 Apr 2021 20:58:33 +0530
From: Pratik Sampat <psampat@...ux.ibm.com>
To: Dennis Zhou <dennis@...nel.org>
Cc: Roman Gushchin <guro@...com>, 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
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
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