question concerning proper usage of kernel variables net.bpf.bufsize and vm_kmem_size_max

Jin Guojun [VFFS] jin at
Wed Jul 26 23:20:57 UTC 2006

R. B. Riddick wrote:

>--- Raymond Owens <owensr at> wrote:
>>Can VM_KMEM_SIZE_MAX be set manually with sysctl?
>No, but you could set it with this procedure:
>1. Insert the lines
>  vm.kmem_size=123456789
>  vm.kmem_size_max=1234567890
>  /boot/loader.conf
>2. reboot
>That should change those values...
>(see src/sys/kern/kern_malloc.c)
>I wonder, why your box needs such a big buffer? Do u have network traffic
>bursts or so?
Regardless what purpose is for, the net.bpf.bufsize should never
set above hardware cache size. The best (optimal size) is 50% - 80%
of the hardware cache size, unless original BPF is modified in some
way I do not know.
Such high bufsize will degrade performance.

------------ Jin Guojun ----------- v --- jin at ---
Distributed Systems Department
Lawrence Berkeley National Laboratory,	Berkeley, CA 94720

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