Limiting the number of unicorns, memory usage and swapping

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I suspect htop is showing threads rather than processes - anyhow, I see the same on htop as you do, but only two unicorns according to

ps uaxf|egrep unicorn.?worker

Also my free is like yours:

# free -h
              total        used        free      shared  buff/cache   available
Mem:           985M        782M         61M         60M        141M         32M
Swap:          2.0G        992M        1.0G

BTW, to see some swap in use is not itself a problem. It’s the actual swapping (paging) which would matter. Try vmstat 5 5 and look at the si and so columns.

# vmstat 5 5
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0 1041832  63176   5716 127408  367  325   601   393    8   10  2  1 95  2  0
 0  0 1041576  60976   5724 127408  399    0   399    21  212  653  1  1 96  2  0
 0  0 1043544  77036   2296 120688  807  803   807   837  404 1144  1  2 94  3  0
 0  0 1043288  65040   3704 129476  254    0  2292     5  255  780  1  1 96  2  0
 0  0 1048736  81936   2916 119016  762 1499   919  1565  470 1171  3  2 90  5  0

I’d prefer not to see anything over 1000 but I’m not too worried. A second run showed a much calmer picture:

# vmstat 5 5
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0 1048452  82712   2532 120848  367  325   601   393    8   10  2  1 95  2  0
 0  0 1047684  74552   2548 124816  285    0  1049    10  230  655  2  1 95  2  0
 0  0 1046660  66556   3692 129008  196    0  1261    16  219  672  1  1 96  2  0
 1  0 1046404  65812   3700 129284   54    0    97    13  137  364  1  0 98  0  0
 0  0 1046148  65280   3700 129288   50    0    50     3  132  344  1  0 98  0  0

Edit: the H key in htop will switch from threads to processes:

  CPU[                                                       0.0%]   Tasks: 66; 1 running
  Mem[||||||||||||||||||||||||||||||||||||||||||||||||||824M/985M]   Load average: 0.19 0.12 0.05 
  Swp[||||||||||||||||||||||||||||||                  1015M/2.00G]   Uptime: 52 days, 00:50:42

  PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
13246 1000       20   0  966M  362M  6448 S  0.0 36.8 51:01.52 unicorn worker[0] -E production -c config/unicorn.conf.rb
13237 1000       25   5 1004M  194M  3780 S  0.0 19.8 22:38.19 sidekiq 6.5.9 discourse [0 of 5 busy]
13258 1000       20   0  919M 70176  3632 S  0.0  7.0  5:02.87 unicorn worker[1] -E production -c config/unicorn.conf.rb
12412 systemd-r  20   0  212M 60928 56916 S  0.0  6.0  0:00.23 postgres: 13/main: discourse discourse [local] idle
12818 systemd-r  20   0  212M 39228 34868 S  0.0  3.9  0:00.07 postgres: 13/main: discourse discourse [local] idle
12719 systemd-r  20   0  211M 28400 25336 S  0.0  2.8  0:00.03 postgres: 13/main: discourse discourse [local] idle
13117 1000       20   0  541M 13768  2048 S  0.0  1.4  1:08.11 unicorn master -E production -c config/unicorn.conf.rb

Edit: I set db_shared_buffers: "128MB" very early on, and haven’t seen any problem with that.