Patch: lwbuf page limits

[Venkatesh Srinivas]

Hi,This patch adds a sysctl (kern.ipc.lwbuf_max_pages), a per-CPU limit on the number of pages of KVA that can be allocated by lwbufs. It is currently set at 8MB. It'd be nice for lwbuf_alloc to not keep requesting pages from the system; in a test, I got a webserver to hit a 256 page limit fairly readily, serving tarballs of /usr/src, to a few (4) clients concurrently. 

http://endeavour.zapto.org/dfly/lwbuf_limit4.diff-- vs