MAXBSIZE increase

[Alexander Motin]

Hi.

Experimenting with NFS and ZFS I found an inter-operation issue: ZFS by
default uses block of 128KB, while FreeBSD NFS (both client and server)
is limited to 64KB requests by the value of MAXBSIZE. On file rewrite
that limitation makes ZFS to do slow read-modify-write cycles for every
write operation, instead of just writing the new data.  Trivial iozone
test show major difference between initial write and rewrite speeds
because of this issue.

Looking through the sources I've found and in r280347 fixed number of
improper MAXBSIZE use cases in device drivers. After that I see no any
reason why MAXBSIZE can not be increased to at least 128KB to match ZFS
default (ZFS now supports block up to 1MB, but that is not default and
so far rare). I've made a test build and also successfully created UFS
file system with 128KB block -- not sure it is needed, but seems it
survives this change well too.

Is there anything I am missing, or it is safe to rise this limit now?

-- 
Alexander Motin