Updating discourse - node.js auto-bumped to 2G on a 1G machine

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Ed_S is experiencing issues with Discourse’s rebuild script on a machine with 1G RAM and 2G swap. The script sets --max-old-space-size to 2048MB for Node.js, which is higher than the machine’s total RAM, causing excessive swapping and suppressing garbage collection. This is not recommended, as suggested by Stack Exchange, which advises setting --max-old-space-size to about 1.5GB on a 2GB machine to avoid swapping. The rebuild completed successfully in about 30 minutes but caused significant swap activity during the process.

1

I’m running on the smallest supported config: 1G RAM and 2G swap. It looks to me like something in the rebuild script tells node.js to use more RAM than I have, which it seems suppresses garbage collection and causes a lot of swapping. Is this as it should be?

I noticed this in the console log:

I, [2024-06-14T15:19:15.613029 #1]  INFO -- : > cd /var/www/discourse && su discourse -c 'bundle exec rake assets:precompile:build'
Node.js heap_size_limit (504.75) is less than 2048MB. Setting --max-old-space-size=2048 and CHEAP_SOURCE_MAPS=1
...[ConfigLoader]
...[Babel: @embroider/macros > applyPatches]

Stack Exchange suggests this is not good:

The configured max-old-space-size had a higher limit than the total amount of RAM that the machine had.
…
In summary, on a machine with 2GB of memory I would probably set --max-old-space-size to about 1.5GB to leave some memory for other uses and avoid swapping.

Around this time I see there’s a huge amount of swap activity

# df -h / ; free ; uptime ; ps auxrc ; vmstat 5 5
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        25G   20G  4.7G  81% /

              total        used        free      shared  buff/cache   available
Mem:        1009140      860952       81820        1104       66368       43068
Swap:       2097144      707016     1390128

 15:21:53 up 155 days, 23:02,  2 users,  load average: 1.69, 1.85, 1.36

USER       PID %CPU %MEM      VSZ    RSS TTY      STAT START   TIME COMMAND
message+   920  0.0  0.1    50192   1872 ?        Rs   Jan10   5:57 dbus-daemon
root     16979  0.0  0.0        0      0 ?        R    14:14   0:02 kworker/u2:2
1000     24317 84.1 71.4 43775512 720984 ?        Rl   15:19   2:07 ember
root     24346  0.0  0.3    40100   3468 pts/0    R+   15:21   0:00 ps
procs -----------memory----------   ---swap-- -----io----  -system-- ------cpu-----
 r  b   swpd   free   buff  cache    si    so    bi    bo   in    cs us sy id wa st
 2  1 710656  79768   7712  60940   350   283   586   352    1     2  3  2 90  4  0
 1  5 798060  65440   3848  52544 21749 19198 23815 19247 3896 16477 30 17  0 52  1
 0  1 885676  73820   1256  37388 19674 18806 20887 18811 3851 16681 21 20  0 55  3
 1  0 704056 103080  11512  70892  8414  3910 17269  3914 1855  7618 64 11  0 25  1
 1  0 693816  95020  11520  70908  1589     0  1589    54  470  1032 95  1  0  4  0

(This is during a command line rebuild and update from approx 3.2.0.beta5-dev(bcb31f79ce) to (Latest) 3.3.0.beta3-dev(49fdccbb1d). The rebuild completed successfully in about 30mins.)