[Bug 229670] ZFS ARC limit vfs.zfs.arc_max from /boot/loader.conf is not respected

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=229670

--- Comment #13 from Leif Pedersen <leif at ofWilsonCreek.com> ---
So I looked back at this today, and I found that even after having returned
maxvnodes to the default, I still see it overrunning arc_max persistently by
almost 2x. I can lower maxvnodes below the default (179499), and then arc_max
is respected. Below are stats on the same system which has 6GB of RAM with
arc_max set to 256MB, starting with maxvnodes at the default and then lowering
it.

Granted, one can reasonably argue that anyone capable of tinkering with arc_max
should be capable of tinkering with maxvnodes also. However, it is rather
astonishing since there are suggestions to crank up maxvnodes to improve
performance [wiki/ZFSTuningGuide] and to lower arc_max for small systems, but
no mention of one affecting the other. So I'm adding this data to be of help if
this is considered a significant bug.


$ sysctl vfs.zfs.arc_max
vfs.zfs.arc_max: 268435456
$ sysctl kern.maxvnodes
kern.maxvnodes: 179499
$ top
last pid: 95789;  load averages:  0.14,  0.16,  0.11                           
                                                    up 8+21:45:16  10:27:57
40 processes:  2 running, 38 sleeping
CPU:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
Mem: 20M Active, 251M Inact, 2769M Wired, 2856M Free
ARC: 456M Total, 87M MFU, 105M MRU, 1600K Anon, 8149K Header, 255M Other
     40M Compressed, 154M Uncompressed, 3.87:1 Ratio
Swap: 

Lowering kern.maxvnodes below the default:

$ sysctl kern.maxvnodes=10240
kern.maxvnodes: 179499 -> 10240
$ top
last pid: 96130;  load averages:  0.06,  0.12,  0.09                           
                                                    up 8+21:50:03  10:32:44
42 processes:  1 running, 41 sleeping
CPU:  0.4% user,  0.0% nice,  0.4% system,  0.0% interrupt, 99.2% idle
Mem: 21M Active, 233M Inact, 2773M Wired, 2868M Free
ARC: 148M Total, 43M MFU, 29M MRU, 1600K Anon, 7678K Header, 66M Other
     40M Compressed, 154M Uncompressed, 3.86:1 Ratio
Swap:

-- 
You are receiving this mail because:
You are the assignee for the bug.