vm_privilege for swapin thread

[Michael Kelly <mike@weatherwax.co.uk>]

Memory allocation is suspended when free memory is low in a memory 
segment. I observed a number of occasions during recent stress testing 
when the kernel effectively froze because a different thread could not 
be swapped in. The swapin thread was suspended awaiting memory for stack 
allocation.

I didn't think it was unreasonable to promote the swapin_thread to 
having vm_privilege to help overcome those situations but perhaps there 
is a reason not to?

Mike.

diff --git a/kern/thread_swap.c b/kern/thread_swap.c
index bfb39239..7bf734f8 100644
--- a/kern/thread_swap.c
+++ b/kern/thread_swap.c
@@ -193,6 +193,7 @@ static void __attribute__((noreturn)) 
swapin_thread_continue(void)

 void swapin_thread(void)
 {
+       current_thread()->vm_privilege = 1;
        stack_privilege(current_thread());

        swapin_thread_continue();