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Re: More puzzing nmbclusters

Konrad Neuwirth <> writes:

> | pinie# sysctl -w kern.mbuf.nmbclusters=32768
> | sysctl: kern.mbuf.nmbclusters: Invalid argument
> No. The only result that doesn't produce an Invalid argument is … 16384. 
> What can I do? 
> This is a NetBSD/i386 machine with 2GB physical RAM. 

Probably you are hitting hard limits in the code.   I would look through
the kernel source.  Beware that just increasing the NMBCLUSTERS without
also increasing kernel virtual address space is likely to lead to KVA
exhaustion, which is not pretty, and manifests itself as a machine which
is not quite crashed but won't do much.

See kern/uipc_mbuf.c:nmbclusters_limit().
You can add printfs; probably that is called infrequently.

It is quite possible that this code can be improved on for various
situations.   But it's also quite likely that changes made without
thorough understanding will cause trouble.

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