[PATCH] Root reservations for strict overcommit

This was on my TODO list for a while and it turns out someone already fixed
the armwaving overcommit mode for the same problem.  It is easy to get into
a situation where you have no overcommit and nothing can be done because
there is no memory to clean up the stable but non-useful state of the
machine.

The fix is trivial and duplicated from the armwaving overcommit code path. 
The last 3% of the memory can be claimed by root processes only.  It isn't
a cure but it does seem to solve the real world problems - at least
providing you have enough memory for 3% to be useful 8).
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

security/commoncap.c

@@ -357,6 +357,11 @@ int cap_vm_enough_memory(long pages)
 
 	allowed = (totalram_pages - hugetlb_total_pages())
 	       	* sysctl_overcommit_ratio / 100;
+	/*
+	 * Leave the last 3% for root
+	 */
+	if (!capable(CAP_SYS_ADMIN))
+		allowed -= allowed / 32;
 	allowed += total_swap_pages;
 
 	if (atomic_read(&vm_committed_space) < allowed)