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[PATCH 0/3] Reduce system overhead of automatic NUMA balancing

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: [PATCH 0/3] Reduce system overhead of automatic NUMA balancing
From: Mel Gorman <mgorman@xxxxxxx>
Date: Mon, 23 Mar 2015 12:24:00 +0000
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Aneesh Kumar <aneesh.kumar@xxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Linux-MM <linux-mm@xxxxxxxxx>, xfs@xxxxxxxxxxx, linuxppc-dev@xxxxxxxxxxxxxxxx, Mel Gorman <mgorman@xxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
These are three follow-on patches based on the xfsrepair workload Dave
Chinner reported was problematic in 4.0-rc1 due to changes in page table
management -- https://lkml.org/lkml/2015/3/1/226.

Much of the problem was reduced by commit 53da3bc2ba9e ("mm: fix up numa
read-only thread grouping logic") and commit ba68bc0115eb ("mm: thp:
Return the correct value for change_huge_pmd"). It was known that the 
performance
in 3.19 was still better even if is far less safe. This series aims to
restore the performance without compromising on safety.

Dave, you already tested patch 1 on its own but it would be nice to test
patches 1+2 and 1+2+3 separately just to be certain.

For the test of this mail, I'm comparing 3.19 against 4.0-rc4 and the
three patches applied on top

autonumabench
                                              3.19.0             4.0.0-rc4      
       4.0.0-rc4             4.0.0-rc4             4.0.0-rc4
                                             vanilla               vanilla      
    vmwrite-v5r8         preserve-v5r8         slowscan-v5r8
Time System-NUMA01                  124.00 (  0.00%)      161.86 (-30.53%)      
107.13 ( 13.60%)      103.13 ( 16.83%)      145.01 (-16.94%)
Time System-NUMA01_THEADLOCAL       115.54 (  0.00%)      107.64 (  6.84%)      
131.87 (-14.13%)       83.30 ( 27.90%)       92.35 ( 20.07%)
Time System-NUMA02                    9.35 (  0.00%)       10.44 (-11.66%)      
  8.95 (  4.28%)       10.72 (-14.65%)        8.16 ( 12.73%)
Time System-NUMA02_SMT                3.87 (  0.00%)        4.63 (-19.64%)      
  4.57 (-18.09%)        3.99 ( -3.10%)        3.36 ( 13.18%)
Time Elapsed-NUMA01                 570.06 (  0.00%)      567.82 (  0.39%)      
515.78 (  9.52%)      517.26 (  9.26%)      543.80 (  4.61%)
Time Elapsed-NUMA01_THEADLOCAL      393.69 (  0.00%)      384.83 (  2.25%)      
384.10 (  2.44%)      384.31 (  2.38%)      380.73 (  3.29%)
Time Elapsed-NUMA02                  49.09 (  0.00%)       49.33 ( -0.49%)      
 48.86 (  0.47%)       48.78 (  0.63%)       50.94 ( -3.77%)
Time Elapsed-NUMA02_SMT              47.51 (  0.00%)       47.15 (  0.76%)      
 47.98 ( -0.99%)       48.12 ( -1.28%)       49.56 ( -4.31%)

              3.19.0   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4
             vanilla     vanillavmwrite-v5r8preserve-v5r8slowscan-v5r8
User        46334.60    46391.94    44383.95    43971.89    44372.12
System        252.84      284.66      252.61      201.24      249.00
Elapsed      1062.14     1050.96      998.68     1000.94     1026.78

Overall the system CPU usage is comparable and the test is naturally a bit 
variable. The
slowing of the scanner hurts numa01 but on this machine it is an adverse 
workload and
patches that dramatically help it often hurt absolutely everything else.

Due to patch 2, the fault activity is interesting

                                3.19.0   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4   
4.0.0-rc4
                               vanilla     
vanillavmwrite-v5r8preserve-v5r8slowscan-v5r8
Minor Faults                   2097811     2656646     2597249     1981230     
1636841
Major Faults                       362         450         365         364      
   365

Note the impact preserving the write bit across protection updates and fault 
reduces
faults.

NUMA alloc hit                 1229008     1217015     1191660     1178322     
1199681
NUMA alloc miss                      0           0           0           0      
     0
NUMA interleave hit                  0           0           0           0      
     0
NUMA alloc local               1228514     1216317     1190871     1177448     
1199021
NUMA base PTE updates        245706197   240041607   238195516   244704842   
115012800
NUMA huge PMD updates           479530      468448      464868      477573      
224487
NUMA page range updates      491225557   479886983   476207932   489222218   
229950144
NUMA hint faults                659753      656503      641678      656926      
294842
NUMA hint local faults          381604      373963      360478      337585      
186249
NUMA hint local percent             57          56          56          51      
    63
NUMA pages migrated            5412140     6374899     6266530     5277468     
5755096
AutoNUMA cost                    5121%       5083%       4994%       5097%      
 2388%

Here the impact of slowing the PTE scanner on migratrion failures is obvious as 
"NUMA base PTE updates" and
"NUMA huge PMD updates" are massively reduced even though the headline 
performance
is very similar.

As xfsrepair was the reported workload here is the impact of the series on it.

xfsrepair
                                       3.19.0             4.0.0-rc4             
4.0.0-rc4             4.0.0-rc4             4.0.0-rc4
                                      vanilla               vanilla          
vmwrite-v5r8         preserve-v5r8         slowscan-v5r8
Min      real-fsmark        1183.29 (  0.00%)     1165.73 (  1.48%)     1152.78 
(  2.58%)     1153.64 (  2.51%)     1177.62 (  0.48%)
Min      syst-fsmark        4107.85 (  0.00%)     4027.75 (  1.95%)     3986.74 
(  2.95%)     3979.16 (  3.13%)     4048.76 (  1.44%)
Min      real-xfsrepair      441.51 (  0.00%)      463.96 ( -5.08%)      449.50 
( -1.81%)      440.08 (  0.32%)      439.87 (  0.37%)
Min      syst-xfsrepair      195.76 (  0.00%)      278.47 (-42.25%)      262.34 
(-34.01%)      203.70 ( -4.06%)      143.64 ( 26.62%)
Amean    real-fsmark        1188.30 (  0.00%)     1177.34 (  0.92%)     1157.97 
(  2.55%)     1158.21 (  2.53%)     1182.22 (  0.51%)
Amean    syst-fsmark        4111.37 (  0.00%)     4055.70 (  1.35%)     3987.19 
(  3.02%)     3998.72 (  2.74%)     4061.69 (  1.21%)
Amean    real-xfsrepair      450.88 (  0.00%)      468.32 ( -3.87%)      454.14 
( -0.72%)      442.36 (  1.89%)      440.59 (  2.28%)
Amean    syst-xfsrepair      199.66 (  0.00%)      290.60 (-45.55%)      277.20 
(-38.84%)      204.68 ( -2.51%)      150.55 ( 24.60%)
Stddev   real-fsmark           4.12 (  0.00%)       10.82 (-162.29%)        
4.14 ( -0.28%)        5.98 (-45.05%)        4.60 (-11.53%)
Stddev   syst-fsmark           2.63 (  0.00%)       20.32 (-671.82%)        
0.37 ( 85.89%)       16.47 (-525.59%)       15.05 (-471.79%)
Stddev   real-xfsrepair        6.87 (  0.00%)        4.55 ( 33.75%)        3.46 
( 49.58%)        1.78 ( 74.12%)        0.52 ( 92.50%)
Stddev   syst-xfsrepair        3.02 (  0.00%)       10.30 (-241.37%)       
13.17 (-336.37%)        0.71 ( 76.63%)        5.00 (-65.61%)
CoeffVar real-fsmark           0.35 (  0.00%)        0.92 (-164.73%)        
0.36 ( -2.91%)        0.52 (-48.82%)        0.39 (-12.10%)
CoeffVar syst-fsmark           0.06 (  0.00%)        0.50 (-682.41%)        
0.01 ( 85.45%)        0.41 (-543.22%)        0.37 (-478.78%)
CoeffVar real-xfsrepair        1.52 (  0.00%)        0.97 ( 36.21%)        0.76 
( 49.94%)        0.40 ( 73.62%)        0.12 ( 92.33%)
CoeffVar syst-xfsrepair        1.51 (  0.00%)        3.54 (-134.54%)        
4.75 (-214.31%)        0.34 ( 77.20%)        3.32 (-119.63%)
Max      real-fsmark        1193.39 (  0.00%)     1191.77 (  0.14%)     1162.90 
(  2.55%)     1166.66 (  2.24%)     1188.50 (  0.41%)
Max      syst-fsmark        4114.18 (  0.00%)     4075.45 (  0.94%)     3987.65 
(  3.08%)     4019.45 (  2.30%)     4082.80 (  0.76%)
Max      real-xfsrepair      457.80 (  0.00%)      474.60 ( -3.67%)      457.82 
( -0.00%)      444.42 (  2.92%)      441.03 (  3.66%)
Max      syst-xfsrepair      203.11 (  0.00%)      303.65 (-49.50%)      294.35 
(-44.92%)      205.33 ( -1.09%)      155.28 ( 23.55%)

The really relevant lines as syst-xfsrepair which is the system CPU usage
when running xfsrepair. Note that on my machine the overhead was 45% higher
on 4.0-rc4 which may be part of what Dave is seeing. Once we preserve the
write bit across faults, it's only 2.51% higher on average. With the full
series applied, system CPU usage is 24.6% lower on average.

Again, the impact of preserving the write bit on minor faults is obvious
and the impact of slowing scanning after migration failures is obvious
on the PTE updates.  Note also that the number of pages migrated is much
reduced even though the headline performance is comparable.

                                3.19.0   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4   
4.0.0-rc4
                               vanilla     
vanillavmwrite-v5r8preserve-v5r8slowscan-v5r8
Minor Faults                 153466827   254507978   249163829   153501373   
105737890
Major Faults                       610         702         690         649      
   724
NUMA base PTE updates        217735049   210756527   217729596   216937111   
144344993
NUMA huge PMD updates           129294       85044      106921      127246      
 79887
NUMA pages migrated           21938995    29705270    28594162    22687324    
16258075

                      3.19.0   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4   4.0.0-rc4
                     vanilla     vanillavmwrite-v5r8preserve-v5r8slowscan-v5r8
Mean sdb-avgqusz       13.47        2.54        2.55        2.47        2.49
Mean sdb-avgrqsz      202.32      140.22      139.50      139.02      138.12
Mean sdb-await         25.92        5.09        5.33        5.02        5.22
Mean sdb-r_await        4.71        0.19        0.83        0.51        0.11
Mean sdb-w_await      104.13        5.21        5.38        5.05        5.32
Mean sdb-svctm          0.59        0.13        0.14        0.13        0.14
Mean sdb-rrqm           0.16        0.00        0.00        0.00        0.00
Mean sdb-wrqm           3.59     1799.43     1826.84     1812.21     1785.67
Max  sdb-avgqusz      111.06       12.13       14.05       11.66       15.60
Max  sdb-avgrqsz      255.60      190.34      190.01      187.33      191.78
Max  sdb-await        168.24       39.28       49.22       44.64       65.62
Max  sdb-r_await      660.00       52.00      280.00       76.00       12.00
Max  sdb-w_await     7804.00       39.28       49.22       44.64       65.62
Max  sdb-svctm          4.00        2.82        2.86        1.98        2.84
Max  sdb-rrqm           8.30        0.00        0.00        0.00        0.00
Max  sdb-wrqm          34.20     5372.80     5278.60     5386.60     5546.15

FWIW, I also checked SPECjbb in different configurations but it's similar 
observations -- minor faults lower,
PTE update activity lower and performance is roughly comparable against 3.19.

 include/linux/sched.h |  9 +++++----
 kernel/sched/fair.c   |  8 ++++++--
 mm/huge_memory.c      | 25 ++++++++++++-------------
 mm/memory.c           | 22 ++++++++++++----------
 mm/mprotect.c         |  3 +++
 5 files changed, 38 insertions(+), 29 deletions(-)

-- 
2.1.2

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