FreeBSD 7.2-RC1 - ZFS related kernel panic "kmem_map too small"

[Ivan Voras]

Gary Jennejohn wrote:
> On Wed, 22 Apr 2009 00:34:00 +0200
> Kai Gallasch <gallasch at free.de> wrote:
> 
> [snip a lot of stuff]
>> In /usr/src/UPDATING I read:
>>
>> [..]
>>
>> 20090207:
>>         ZFS users on amd64 machines with 4GB or more of RAM should
>>         reevaluate their need for setting vm.kmem_size_max and
>>         vm.kmem_size manually.  In fact, after recent changes to the
>>         kernel, the default value of vm.kmem_size is larger than the
>>         suggested manual setting in most ZFS/FreeBSD tuning guides.
>>
>> So I understood this as "vm.kmem_size is set unnecessary large by
>> default. You should think about decreasing it to save some RAM"
>>
>> On my amd64 server the default values of kmem_size are
>>
>> vm.kmem_size_scale: 3
>> vm.kmem_size_max: 3865468109
>> vm.kmem_size_min: 0
>> vm.kmem_size: 1201446912
>>
>> Can someone give me a hint how to debug this problem further, or how to
>> find some reasonable values for setting vm.kmem_size_max and
>> vm.kmem_size with 16G of RAM?
>>
> 
> Hmm, I wonder whether this applies to 7.2-RC1.  I don't know whether
> the kernel changes have been committed to 7.2 or whether they were
> already present when we started work on 7.2 because I haven't been
> paying much attention.

7.2 was branched last Friday - quick browsing of commit messages doesn't
find any relevant new development between Friday and now.

> On my 8-current amd64 machine with only 4GB of RAM I see larger values
> than you see with 16GB:
> 
> sysctl vm.kmem_size_max
> vm.kmem_size_max: 4509713203
> sysctl vm.kmem_size
> vm.kmem_size: 1335824384

Ok, but remember that ZFS in -CURRENT is very different from ZFS in -STABLE.

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