A typical nfsd call trace is
 nfsd -> svc_process -> nfsd_dispatch -> nfsd3_proc_write ->
   nfsd_write ->nfsd_vfs_write -> vfs_writev

These add up to over 300 bytes on the stack.
Looking at each of these, I see that nfsd_write (which includes
 nfsd_vfs_write) contributes 0x8c to stack usage itself!!

It turns out this is because it puts a 'struct iattr' on the stack so
it can kill suid if needed.  The following patch saves about 50 bytes
off the stack in this call path.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>