kmem_map too small with ZFS and 8.2-RELEASE

[Adam McDougall]

On 03/04/11 04:48, Mickaël Canévet wrote:
>> I'd use vm.kmem_size="32G" (i.e. twice your RAM) and that's it.
>
> Should I also increase vfs.zfs.arc_max ?
>
> Do you have any idea why the kernel panicked at only 8GB allocated ?
>
> Thank you

I believe ARC allocations in kmem can become fragmented, so when it is 
searching for a place to store a new contiguous segment of memory, the 
remaining fragmented free spaces may all be too small.  I also set
vm.kmem_size to about twice the amount of ram to help it avoid this 
issue.  I suspect if kmem is badly fragmented then performance of ZFS 
can downgrade, so that is another reason to keep kmem bigger.