Re: [PATCH v2] mm/slub: disable slab merging in the default configuration

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On Thu, 6 Jul 2023, David Rientjes wrote:

> On Mon, 3 Jul 2023, David Rientjes wrote:
> 
> > hackbench
> 
> Running hackbench on Skylake with v6.1.30 (A) and v6.1.30 + your patch 
> (B), for example:
> 
>               LABEL             | COUNT |    MIN     |    MAX     |    MEAN    |   MEDIAN   |  STDDEV   |   DIRECTION    
> --------------------------------+-------+------------+------------+------------+------------+-----------+----------------
>   SReclaimable                  |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 11    | 129480.000 | 233208.000 | 189936.364 | 204316.000 | 31465.625 |                
>   (B) <same sha>                | 11    | 139084.000 | 236772.000 | 198931.273 | 213672.000 | 30013.204 |                
>                                 |       | +7.42%     | +1.53%     | +4.74%     | +4.58%     | -4.62%    | <not defined>  
>   SUnreclaim                    |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 11    | 305400.000 | 538744.000 | 422148.000 | 449344.000 | 65005.045 |                
>   (B) <same sha>                | 11    | 305780.000 | 518300.000 | 422219.636 | 450252.000 | 61245.137 |                
>                                 |       | +0.12%     | -3.79%     | +0.02%     | +0.20%     | -5.78%    | <not defined>  
> 
> Amount of reclaimable slab significantly increases which is likely not a 
> problem because, well, it's reclaimable.  But I suspect we'll find other 
> interesting data points with the other suggested benchmarks.
> 
> And benchmark results:
> 
>               LABEL             | COUNT |    MIN     |    MAX     |    MEAN    |   MEDIAN   |  STDDEV   |   DIRECTION    
> --------------------------------+-------+------------+------------+------------+------------+-----------+----------------
>   hackbench_process_pipes_234   |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 7     | 1.735      | 1.979      | 1.831      | 1.835      | 0.086291  |                
>   (B) <same sha>                | 7     | 1.687      | 2.023      | 1.886      | 1.911      | 0.10276   |                
>                                 |       | -2.77%     | +2.22%     | +3.00%     | +4.14%     | +19.09%   | <not defined>  
>   hackbench_process_pipes_max   |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 7     | 1.735      | 1.979      | 1.831      | 1.835      | 0.086291  |                
>   (B) <same sha>                | 7     | 1.687      | 2.023      | 1.886      | 1.911      | 0.10276   |                
>                                 |       | -2.77%     | +2.22%     | +3.00%     | +4.14%     | +19.09%   | - is good      
>   hackbench_process_sockets_234 |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 7     | 7.883      | 7.909      | 7.899      | 7.899      | 0.0087808 |                
>   (B) <same sha>                | 7     | 7.872      | 7.961      | 7.907      | 7.904      | 0.028019  |                
>                                 |       | -0.14%     | +0.66%     | +0.10%     | +0.06%     | +219.09%  | <not defined>  
>   hackbench_process_sockets_max |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 7     | 7.883      | 7.909      | 7.899      | 7.899      | 0.0087808 |                
>   (B) <same sha>                | 7     | 7.872      | 7.961      | 7.907      | 7.904      | 0.028019  |                
>                                 |       | -0.14%     | +0.66%     | +0.10%     | +0.06%     | +219.09%  | - is good      
>   hackbench_thread_pipes_234    |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 7     | 2.146      | 2.677      | 2.410      | 2.418      | 0.18143   |                
>   (B) <same sha>                | 7     | 2.016      | 2.514      | 2.268      | 2.241      | 0.17474   |                
>                                 |       | -6.06%     | -6.09%     | -5.88%     | -7.32%     | -3.69%    | <not defined>  
>   hackbench_thread_pipes_max    |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 7     | 2.146      | 2.677      | 2.410      | 2.418      | 0.18143   |               
>   (B) <same sha>                | 7     | 2.016      | 2.514      | 2.268      | 2.241      | 0.17474   |                
>                                 |       | -6.06%     | -6.09%     | -5.88%     | -7.32%     | -3.69%    | - is good      
>   hackbench_thread_sockets_234  |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 7     | 8.025      | 8.127      | 8.084      | 8.085      | 0.029755  |                
>   (B) <same sha>                | 7     | 7.990      | 8.093      | 8.042      | 8.035      | 0.035152  |                
>                                 |       | -0.44%     | -0.42%     | -0.53%     | -0.62%     | +18.14%   | <not defined>  
>   hackbench_thread_sockets_max  |       |            |            |            |            |           |                
>   (A) v6.1.30                   | 7     | 8.025      | 8.127      | 8.084      | 8.085      | 0.029755  |                
>   (B) <same sha>                | 7     | 7.990      | 8.093      | 8.042      | 8.035      | 0.035152  |                
>                                 |       | -0.44%     | -0.42%     | -0.53%     | -0.62%     | +18.14%   | - is good    

My takeaway from running half a dozen benchmarks on Intel is that
performance is more impacted than slab memory usage.  There are slight
regressions in memory usage, but only measurable for SReclaimable which
would be the better form (as opposed to SUnreclaimable).

There are some substantial performance degradations, most notably 
context_switch1_per_thread_ops which regressed ~21%.  I'll need to repeat
that test to confirm it and can also try on cascadelake if it reproduces.

There are some more negligible redis, specjbb, and will-it-scale
regressions which don't look terribly concerning.

I'll try running performance tests on AMD Zen3 and also ARM with
PAGE_SIZE == 4KB and 64KB.

Unixbench memory usage and performance is within +/- 1% for every metric,
so it's not presented here.

Full results for Skylake, removing results where mean is +/- 1% of
baseline:

============================== MEMORY USAGE ==============================

hackbench
              LABEL             | COUNT |    MIN     |    MAX     |    MEAN    |   MEDIAN   |  STDDEV   |   DIRECTION    
--------------------------------+-------+------------+------------+------------+------------+-----------+----------------
  SReclaimable                  |       |            |            |            |            |           |                
  (A) v6.1.30                   | 11    | 129480.000 | 233208.000 | 189936.364 | 204316.000 | 31465.625 |                
  (B) v6.1.30 slab_nomerge      | 11    | 139084.000 | 236772.000 | 198931.273 | 213672.000 | 30013.204 |                
                                |       | +7.42%     | +1.53%     | +4.74%     | +4.58%     | -4.62%    | - is good

redis
             LABEL             | COUNT |    MIN     |    MAX     |    MEAN    |   MEDIAN   |  STDDEV   |   DIRECTION    
-------------------------------+-------+------------+------------+------------+------------+-----------+----------------
  SReclaimable                 |       |            |            |            |            |           |                
  (A) v6.1.30                  | 298   | 137056.000 | 238664.000 | 226005.477 | 226940.000 | 8109.328  |                
  (B) v6.1.30 slab_nomerge     | 302   | 139664.000 | 242664.000 | 229096.689 | 230098.000 | 8215.134  |                
                               |       | +1.90%     | +1.68%     | +1.37%     | +1.39%     | +1.30%    | - is good 

specjbb2015
               LABEL               | COUNT |    MIN     |    MAX     |    MEAN    |   MEDIAN   |  STDDEV  |   DIRECTION    
-----------------------------------+-------+------------+------------+------------+------------+----------+----------------
  SReclaimable                     |       |            |            |            |            |          |                
  (A) v6.1.30                      | 1602  | 118344.000 | 217932.000 | 203559.618 | 205372.000 | 5314.410 |                
  (B) v6.1.30 slab_nomerge         | 1655  | 128000.000 | 222536.000 | 208099.973 | 209396.000 | 4608.582 |                
                                   |       | +8.16%     | +2.11%     | +2.23%     | +1.96%     | -13.28%  | - is good 

============================== PERFORMANCE ==============================

hackbench
              LABEL             | COUNT |    MIN     |    MAX     |    MEAN    |   MEDIAN   |  STDDEV   |   DIRECTION    
--------------------------------+-------+------------+------------+------------+------------+-----------+----------------
  hackbench_process_pipes_234   |       |            |            |            |            |           |                
  (A) v6.1.30                   | 7     | 1.735      | 1.979      | 1.831      | 1.835      | 0.086291  |                
  (B) v6.1.30 slab_nomerge      | 7     | 1.687      | 2.023      | 1.886      | 1.911      | 0.10276   |                
                                |       | -2.77%     | +2.22%     | +3.00%     | +4.14%     | +19.09%   | - is good 
  hackbench_thread_pipes_234    |       |            |            |            |            |           |                
  (A) v6.1.30                   | 7     | 2.146      | 2.677      | 2.410      | 2.418      | 0.18143   |                
  (B) v6.1.30 slab_nomerge      | 7     | 2.016      | 2.514      | 2.268      | 2.241      | 0.17474   |                
                                |       | -6.06%     | -6.09%     | -5.88%     | -7.32%     | -3.69%    | - is good

redis
             LABEL             | COUNT |    MIN     |    MAX     |    MEAN    |   MEDIAN   |  STDDEV   |   DIRECTION    
-------------------------------+-------+------------+------------+------------+------------+-----------+----------------
  redis_medium_max_INCR        |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 108695.660 | 112637.980 | 110639.626 | 109757.440 | 1668.190  |                
  (B) v6.1.30 slab_nomerge     | 5     | 101853.740 | 106564.370 | 104166.478 | 104942.800 | 1833.377  |                
                               |       | -6.29%     | -5.39%     | -5.85%     | -4.39%     | +9.90%    | + is good      
  redis_medium_max_LPOP        |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 102944.200 | 108471.630 | 105572.750 | 106303.820 | 2016.986  |                
  (B) v6.1.30 slab_nomerge     | 5     | 101471.340 | 104231.810 | 103361.688 | 104090.770 | 1064.277  |                
                               |       | -1.43%     | -3.91%     | -2.09%     | -2.08%     | -47.23%   | + is good      
  redis_medium_max_LPUSH       |       |            |            |            |            |           |                
  (A) v6.1.30                  | 10    | 99255.590  | 108295.430 | 105960.440 | 106338.120 | 2553.802  |                
  (B) v6.1.30 slab_nomerge     | 10    | 100130.160 | 107032.000 | 104335.070 | 105091.705 | 2169.708  |                
                               |       | +0.88%     | -1.17%     | -1.53%     | -1.17%     | -15.04%   | + is good      
  redis_medium_max_LRANGE_100  |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 72427.030  | 73046.020  | 72671.814  | 72626.910  | 202.812   |                
  (B) v6.1.30 slab_nomerge     | 5     | 70811.500  | 72030.540  | 71519.286  | 71761.750  | 450.918   |                
                               |       | -2.23%     | -1.39%     | -1.59%     | -1.19%     | +122.33%  | + is good      
  redis_medium_max_MSET_10     |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 87642.420  | 89798.850  | 89044.390  | 89102.740  | 769.933   |                
  (B) v6.1.30 slab_nomerge     | 5     | 85287.840  | 89758.550  | 87876.598  | 88386.070  | 1641.608  |                
                               |       | -2.69%     | -0.04%     | -1.31%     | -0.80%     | +113.21%  | + is good      
  redis_medium_max_PING_BULK   |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 101729.400 | 108189.980 | 105003.228 | 105307.490 | 2171.756  |                
  (B) v6.1.30 slab_nomerge     | 5     | 100553.050 | 105340.770 | 102561.464 | 101947.190 | 1789.953  |                
                               |       | -1.16%     | -2.63%     | -2.33%     | -3.19%     | -17.58%   | + is good      
  redis_medium_max_PING_INLINE |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 102522.050 | 107503.770 | 105209.902 | 106033.300 | 1981.499  |                
  (B) v6.1.30 slab_nomerge     | 5     | 97541.950  | 107319.170 | 103729.414 | 104854.780 | 3304.256  |                
                               |       | -4.86%     | -0.17%     | -1.41%     | -1.11%     | +66.76%   | + is good      
  redis_medium_max_SET         |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 105663.570 | 112283.850 | 108917.118 | 109469.070 | 2663.234  |                
  (B) v6.1.30 slab_nomerge     | 5     | 103071.540 | 106723.590 | 105128.226 | 106179.660 | 1666.892  |                
                               |       | -2.45%     | -4.95%     | -3.48%     | -3.00%     | -37.41%   | + is good      
  redis_medium_max_SPOP        |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 104079.940 | 107238.610 | 105140.616 | 104964.840 | 1150.370  |                
  (B) v6.1.30 slab_nomerge     | 5     | 102637.790 | 103885.300 | 103343.934 | 103412.620 | 437.159   |                
                               |       | -1.39%     | -3.13%     | -1.71%     | -1.48%     | -62.00%   | + is good      
   redis_small_max_INCR        |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 98814.230  | 114942.530 | 107744.856 | 108813.920 | 6150.540  |                
  (B) v6.1.30 slab_nomerge     | 5     | 99800.400  | 109529.020 | 104451.708 | 104058.270 | 3732.461  |                
                               |       | +1.00%     | -4.71%     | -3.06%     | -4.37%     | -39.31%   | + is good      
  redis_small_max_LPOP         |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 104275.290 | 118764.840 | 108648.192 | 106951.880 | 5208.918  |                
  (B) v6.1.30 slab_nomerge     | 5     | 97560.980  | 115074.800 | 103120.496 | 99800.400  | 6353.203  |                
                               |       | -6.44%     | -3.11%     | -5.09%     | -6.69%     | +21.97%   | + is good      
  redis_small_max_LRANGE_100   |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 67980.970  | 72992.700  | 71589.644  | 72150.070  | 1832.810  |                
  (B) v6.1.30 slab_nomerge     | 5     | 64977.260  | 72046.110  | 70273.716  | 71684.590  | 2680.854  |                
                               |       | -4.42%     | -1.30%     | -1.84%     | -0.65%     | +46.27%   | + is good       
  redis_small_max_MSET_10      |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 90497.730  | 106044.540 | 100756.422 | 102880.660 | 5455.768  |                
  (B) v6.1.30 slab_nomerge     | 5     | 97276.270  | 106951.880 | 102818.856 | 102880.660 | 3293.135  |                
                               |       | +7.49%     | +0.86%     | +2.05%     | +0.00%     | -39.64%   | + is good        
  redis_small_max_PING_INLINE  |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 96153.850  | 108459.870 | 102493.414 | 102459.020 | 4995.757  |                
  (B) v6.1.30 slab_nomerge     | 5     | 84317.030  | 116144.020 | 99995.920  | 98039.220  | 11045.861 |                
                               |       | -12.31%    | +7.08%     | -2.44%     | -4.31%     | +121.10%  | + is good      
  redis_small_max_SADD         |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 106044.540 | 115606.940 | 109804.052 | 110375.270 | 3451.251  |                
  (B) v6.1.30 slab_nomerge     | 5     | 95693.780  | 109769.480 | 102329.518 | 102249.490 | 4602.161  |                
                               |       | -9.76%     | -5.05%     | -6.81%     | -7.36%     | +33.35%   | + is good      
  redis_small_max_SET          |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 91911.760  | 116686.120 | 104509.200 | 102354.150 | 8993.532  |                
  (B) v6.1.30 slab_nomerge     | 5     | 100502.520 | 113636.370 | 108815.700 | 109649.120 | 4750.002  |                
                               |       | +9.35%     | -2.61%     | +4.12%     | +7.13%     | -47.18%   | + is good      
  redis_small_max_SPOP         |       |            |            |            |            |           |                
  (A) v6.1.30                  | 5     | 96899.230  | 108695.650 | 103648.652 | 104931.800 | 3901.567  |                
  (B) v6.1.30 slab_nomerge     | 5     | 93457.940  | 108108.110 | 101680.560 | 101626.020 | 5096.944  |                
                               |       | -3.55%     | -0.54%     | -1.90%     | -3.15%     | +30.64%   | + is good 

specjbb2015
               LABEL               | COUNT |    MIN     |    MAX     |    MEAN    |   MEDIAN   |  STDDEV  |   DIRECTION    
-----------------------------------+-------+------------+------------+------------+------------+----------+----------------
  specjbb2015_single_Critical_JOPS |       |            |            |            |            |          |                
  (A) v6.1.30                      | 1     | 46294.000  | 46294.000  | 46294.000  | 46294.000  | 0        |                
  (B) v6.1.30 slab_nomerge         | 1     | 46167.000  | 46167.000  | 46167.000  | 46167.000  | 0        |                
                                   |       | -0.27%     | -0.27%     | -0.27%     | -0.27%     | ---      | + is good      
  specjbb2015_single_Max_JOPS      |       |            |            |            |            |          |                
  (A) v6.1.30                      | 1     | 68842.000  | 68842.000  | 68842.000  | 68842.000  | 0        |                
  (B) v6.1.30 slab_nomerge         | 1     | 67801.000  | 67801.000  | 67801.000  | 67801.000  | 0        |                
                                   |       | -1.51%     | -1.51%     | -1.51%     | -1.51%     | ---      | + is good   
                                   
vm-scalability
                 LABEL                 | COUNT |       MIN       |       MAX       |      MEAN       |     MEDIAN      |    STDDEV     | DIRECTION  
---------------------------------------+-------+-----------------+-----------------+-----------------+-----------------+---------------+------------
  300s_128G_truncate_throughput        |       |                 |                 |                 |                 |               |            
  (A) v6.1.30                          | 15    | 16398714804.000 | 17010339870.000 | 16772025703.867 | 16834675132.000 | 232697088.501 |            
  (B) v6.1.30 slab_nomerge             | 15    | 16704416343.000 | 17271437122.000 | 16948419991.200 | 16821799877.000 | 233146680.475 |            
                                       |       | +1.86%          | +1.53%          | +1.05%          | -0.08%          | +0.19%        | + is good  
  300s_512G_anon_wx_rand_mt_throughput |       |                 |                 |                 |                 |               |            
  (A) v6.1.30                          | 15    | 7198561.000     | 7359712.000     | 7263944.200     | 7259418.000     | 50394.115     |            
  (B) v6.1.30 slab_nomerge             | 15    | 7191842.000     | 7628158.000     | 7390629.000     | 7407204.000     | 171602.612    |            
                                       |       | -0.09%          | +3.65%          | +1.74%          | +2.04%          | +240.52%      | + is good  

will-it-scale
               LABEL               | COUNT |     MIN      |     MAX      |     MEAN     |    MEDIAN    |  STDDEV   |   DIRECTION    
-----------------------------------+-------+--------------+--------------+--------------+--------------+-----------+----------------
  context_switch1_per_thread_ops   |       |              |              |              |              |           |                
  (A) v6.1.30                      | 1     | 324721.000   | 324721.000   | 324721.000   | 324721.000   | 0         |                
  (B) v6.1.30 slab_nomerge         | 1     | 255999.000   | 255999.000   | 255999.000   | 255999.000   | 0         |                
    !! REGRESSED !!                |       | -21.16%      | -21.16%      | -21.16%      | -21.16%      | ---       | + is good      
  getppid1_scalability             |       |              |              |              |              |           |                
  (A) v6.1.30                      | 1     | 0.71943      | 0.71943      | 0.71943      | 0.71943      | 0         |                
  (B) v6.1.30 slab_nomerge         | 1     | 0.70923      | 0.70923      | 0.70923      | 0.70923      | 0         |                
                                   |       | -1.42%       | -1.42%       | -1.42%       | -1.42%       | ---       | + is good      
  mmap1_scalability                |       |              |              |              |              |           |                
  (A) v6.1.30                      | 1     | 0.18831      | 0.18831      | 0.18831      | 0.18831      | 0         |                
  (B) v6.1.30 slab_nomerge         | 1     | 0.18413      | 0.18413      | 0.18413      | 0.18413      | 0         |                
                                   |       | -2.22%       | -2.22%       | -2.22%       | -2.22%       | ---       | + is good      
  poll2_scalability                |       |              |              |              |              |           |                
  (A) v6.1.30                      | 1     | 0.45608      | 0.45608      | 0.45608      | 0.45608      | 0         |                
  (B) v6.1.30 slab_nomerge         | 1     | 0.44207      | 0.44207      | 0.44207      | 0.44207      | 0         |                
                                   |       | -3.07%       | -3.07%       | -3.07%       | -3.07%       | ---       | + is good      
  pthread_mutex1_scalability       |       |              |              |              |              |           |                
  (A) v6.1.30                      | 1     | 0.45207      | 0.45207      | 0.45207      | 0.45207      | 0         |                
  (B) v6.1.30 slab_nomerge         | 1     | 0.44194      | 0.44194      | 0.44194      | 0.44194      | 0         |                
                                   |       | -2.24%       | -2.24%       | -2.24%       | -2.24%       | ---       | + is good      
  pthread_mutex2_per_process_ops   |       |              |              |              |              |           |                
  (A) v6.1.30                      | 1     | 36292960.000 | 36292960.000 | 36292960.000 | 36292960.000 | 0         |                
  (B) <v6.1.30 slab_nomerge        | 1     | 35446930.000 | 35446930.000 | 35446930.000 | 35446930.000 | 0         |                
                                   |       | -2.33%       | -2.33%       | -2.33%       | -2.33%       | ---       | + is good      
  signal1_scalability              |       |              |              |              |              |           |                
  (A) v6.1.30                      | 1     | 0.55541      | 0.55541      | 0.55541      | 0.55541      | 0         |                
  (B) v6.1.30 slab_nomerge         | 1     | 0.54773      | 0.54773      | 0.54773      | 0.54773      | 0         |                
                                   |       | -1.38%       | -1.38%       | -1.38%       | -1.38%       | ---       | + is good      
  unix1_scalability                |       |              |              |              |              |           |                
  (A) v6.1.30                      | 1     | 0.55085      | 0.55085      | 0.55085      | 0.55085      | 0         |                
  (B) v6.1.30 slab_nomerge         | 1     | 0.53957      | 0.53957      | 0.53957      | 0.53957      | 0         |                
                                   |       | -2.05%       | -2.05%       | -2.05%       | -2.05%       | ---       | + is good   




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