do not keep sorted contiguous free list

increase PHYSTOP

put an invalid page below the stack
have fork() handle invalid pages

passes all tests on two-processor smp

group locks into structs they protect.
few naming nits.

nits in comments

lots of cleanup

so fast interrupts overflow the kernel stack
fix: cli() before lapic_eoi()

nesting cli/sti: release shouldn't always enable interrupts
separate setup of lapic from starting of other cpus, so cpu() works earlier
flag to disable locking in console output
make locks work even when curproc==0
(still crashes in clock interrupt)

succeeds at usertests.c pipe test

usertest.c tests pre-emption
kill()

swtch idles on per-CPU stack, not on calling process's stack
fix pipe bugs
usertest.c tests pipes, fork, exit, close