kmem_map too small with ZFS and 8.2-RELEASE

[Kai Gallasch]

Am 04.03.2011 um 09:23 schrieb Mickaël Canévet:

> Hello,
> 
> I know there is a lot of threads about "kmem_map too small" problems on
> former versions of FreeBSD with ZFS, but on the wiki
> (http://wiki.freebsd.org/ZFSTuningGuide) it is said that "FreeBSD 7.2+
> has improved kernel memory allocation strategy and no tuning may be
> necessary on systems with more than 2 GB of RAM."
> 
> I have a 64bits machine with 16GB of RAM with FreeBSD 8.2-RELEASE and no
> tuning:
> 
> # sysctl -a | grep -e "vm.kmem_size_max:" -e "vm.kmem_size:" -e
> "vfs.zfs.arc_max:"
> vm.kmem_size_max: 329853485875
> vm.kmem_size: 16624558080
> vfs.zfs.arc_max: 15550816256
> 
> This morning this server crashed with:
> 
> panic: kmem_malloc(1048576): kmem_map too small: 8658309120 total
> allocated

Hi, Mickaël.

If you want to "get a picture" on how setting ZFS tunables in loader.conf affect the different cache sizes and cache hit ratios, I can recommend installing the freebsd port sysutils/munin-node together with sysutils/zfs-stats and the following munin ZFS plugins:

http://exchange.munin-monitoring.org/plugins/search?keyword=FreeBSD

Regards,
Kai.