witness_lock_list_get: witness exhausted

[Michael Jung]

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
***@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.


Thanks!
--mikej

[John Baldwin]

Post by Michael Jung
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
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.

[Mateusz Guzik]

Post by John Baldwin

Post by Michael Jung
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
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
/*
* 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.

Thank you for you explanation. We are expanding our ESXi cluster and even
though with standard edition I can only assign 64 vCPU's to a guest and as
much
RAM as I want, I do like to help with edge cases if I can make them occur
pushing
boundaries as I can towards additianional improvements in FreeBSD.

Can you apply this and re-run the test?

https://people.freebsd.org/~mjg/witness.diff

It bumps the counters to be "high enough" but also starts tracking usage.
If you get
the message again, bump the values even higher.

Once you get a complete poudriere run which did not result in the problem,
do:
$ sysctl debug.witness.list_used debug.witness.list_max_used

to dump the actual usage.