lightly loaded system eats swap space

[David Fullard]

I've noticed you've got a rather large ZFS ARC. You could try limiting the ZFS max ARC size by setting the vfs.zfs.arc_max sysctl.

On Sun, Jun 17, 2018, at 6:19 PM, tech-lists wrote:
> Hello list,
> 
> context is (server)
> freebsd-11-stable r333874, ZFS raidz1-0 (3x4TB disks), 128GB RAM, 
> E5-2630 @2.3GHz, generic kernel.
> 
> There's one bhyve guest on this server (using 4x cpu and 16GB RAM, also 
> freebsd-11-stable)
> 
> There have been no special options for zfs configuration on the server, 
> apart from several datasets having the compressed property set (lz4).
> 
> The server runs nothing else really apart from sshd and it uses ntpd to 
> sync local time.
> 
> How come such a lightly loaded server with plenty of resources is eating 
> up swap? If I run two bhyve instances, i.e. two of the same size as 
> indicated above, so 32GB used for the bhyves, I'll get out-of-swapspace 
> errors in the daily logs:
> 
> +swap_pager_getswapspace(24): failed
> +swap_pager_getswapspace(24): failed
> +swap_pager_getswapspace(24): failed
> 
> Here's top, with one bhyve instance running:
> 
> last pid: 49494;  load averages:  0.12,  0.13,  0.88 
>  
>  
>                               up 29+11:36:06  22:52:45
> 54 processes:  1 running, 53 sleeping
> CPU:  0.4% user,  0.0% nice,  0.4% system,  0.3% interrupt, 98.9% idle
> Mem: 8664K Active, 52M Inact, 4797M Laundry, 116G Wired, 1391M Buf, 
> 4123M Free
> ARC: 108G Total, 1653M MFU, 105G MRU, 32K Anon, 382M Header, 632M Other
>       103G Compressed, 104G Uncompressed, 1.00:1 Ratio
> Swap: 4096M Total, 3502M Used, 594M Free, 85% Inuse
> 
>    PID USERNAME    THR PRI NICE   SIZE    RES STATE   C   TIME    WCPU 
> COMMAND
> 49491 root          1   4    0 16444K 12024K select  9   0:12   6.49% ssh
> 32868 root         12  20    0  9241M  4038M kqread  2  23.2H   1.30% bhyve
> 49490 root          1  20    0 10812K  6192K sbwait  5   0:02   0.88% sftp
> 
>  From the looks of it, a huge amount of ram is wired. Why is that, and 
> how would I debug it?
> 
> A server of similar spec which is running freebsd-current with seven 
> bhyve instances doesn't have this issue:
> 
> last pid: 41904;  load averages:  0.26,  0.19,  0.15 
>  
>  
>                               up 17+01:06:11  23:14:13
> 27 processes:  1 running, 26 sleeping
> CPU:  0.1% user,  0.0% nice,  0.3% system,  0.0% interrupt, 99.6% idle
> Mem: 17G Active, 6951M Inact, 41G Laundry, 59G Wired, 1573M Buf, 1315M Free
> ARC: 53G Total, 700M MFU, 52G MRU, 512K Anon, 182M Header, 958K Other
>       53G Compressed, 69G Uncompressed, 1.30:1 Ratio, 122M Overhead
> Swap: 35G Total, 2163M Used, 33G Free, 6% Inuse
> 
> thanks,
> -- 
> J.
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