Is there any way to increase the KVM?

John Baldwin jhb at
Sat May 31 16:52:51 UTC 2008

On Saturday 31 May 2008 01:52:56 am Tz-Huan Huang wrote:
> Hi,
> Our nfs server is running 7-stable/amd64 with 8G ram, the size of zfs
> pool is 12T. We have set vm.kmem_size and vm.kmem_size_max to
> 1.5G, but the kernel still panics by "kmem_map too small" often.
> According to [1], the limitation is not only by the loader (is it fixed
> now?) but also by the default layout of KVM. [2] points a way to increase
> the KVM, but we get the similar linking error.
> Is there any standard way to modify the layout of KVM? For example, we
> may want to set KVM to 6G and leave the 2G for user space usage.

On i386 you only have 4GB of virtual address space period.  For amd64 you can 
jack up KVM just fine AFAIK.  The mcmodel=kernel stuff should only affect 
global variables (so .data and .bss) and not malloc'd stuff.  Have you tried 
increasing the KVM size and seeing what happens?

John Baldwin

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