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
