witness_lock_list_get: witness exhausted

[John Baldwin]

On Tuesday, November 28, 2017 02:46:03 PM Michael Jung wrote:
> Hi!
> 
> I've recently up'd my processor count on our poudriere box and have 
> started noticing the error
> "witness_lock_list_get: witness exhausted" on the console.  The kernel 
> *DOES NOT* crash but I
> thought the report may be useful to someone.
> 
> $ uname -a
> FreeBSD poudriere 12.0-CURRENT FreeBSD 12.0-CURRENT #1 r325999: Sun Nov 
> 19 18:41:20 EST 2017
> mikej at poudriere:/usr/obj/usr/src/amd64.amd64/sys/GENERIC  amd64
> 
> The machine is pretty busy running four poudriere build instances.
> 
> last pid: 76584;  load averages: 115.07, 115.96, 98.30                   
>                                                                           
>                                       up 6+07:32:59  14:44:03
> 763 processes: 117 running, 581 sleeping, 2 zombie, 63 lock
> CPU: 59.0% user,  0.0% nice, 40.7% system,  0.1% interrupt,  0.1% idle
> Mem: 12G Active, 2003M Inact, 44G Wired, 29G Free
> ARC: 28G Total, 11G MFU, 16G MRU, 122M Anon, 359M Header, 1184M Other
>       25G Compressed, 32G Uncompressed, 1.24:1 Ratio
> 
> Let me know what additional information I might supply.

This just means that WITNESS stopped working because it ran out of
pre-allocated objects.  In particular the objects used to track how
many locks are held by how many threads:

/*
 * XXX: This is somewhat bogus, as we assume here that at most 2048 threads
 * will hold LOCK_NCHILDREN locks.  We handle failure ok, and we should
 * probably be safe for the most part, but it's still a SWAG.
 */
#define LOCK_NCHILDREN  5
#define LOCK_CHILDCOUNT 2048

Probably the '2048' (max number of concurrent threads) needs to scale with
MAXCPU.  2048 threads is probably a bit low on big x86 boxes.

-- 
John Baldwin