Re: [PATCH v3 0/6] percpu: partial chunk depopulation
From: Pratik Sampat
Date: Fri Apr 16 2021 - 15:44:24 EST
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