GFP_ATOMIC overallocation

Trigger a failure or reclaim by allocating large amounts of memory from the
timer interrupt.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 kernel/timer.c |   30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

Index: linux-2.6/kernel/timer.c
===================================================================
--- linux-2.6.orig/kernel/timer.c	2007-08-13 21:28:43.000000000 -0700
+++ linux-2.6/kernel/timer.c	2007-08-13 22:04:39.000000000 -0700
@@ -817,6 +817,12 @@ unsigned long next_timer_interrupt(void)
 #endif
 
 /*
+ * Min freekbytes is 2m. 1000 pages give us 4M which is
+ * able to exhaust the reserves
+ */
+#define NR_TEST 3000
+
+/*
  * Called from the timer interrupt handler to charge one tick to the current 
  * process.  user_tick is 1 if the tick is user time, 0 for system.
  */
@@ -824,6 +830,9 @@ void update_process_times(int user_tick)
 {
 	struct task_struct *p = current;
 	int cpu = smp_processor_id();
+	struct page **base;
+	int i;
+	static unsigned long lasttime = 0;
 
 	/* Note: this timer irq context must be accounted for as well. */
 	if (user_tick)
@@ -835,6 +844,27 @@ void update_process_times(int user_tick)
 		rcu_check_callbacks(cpu, user_tick);
 	scheduler_tick();
 	run_posix_cpu_timers(p);
+
+	/* Every 2 minutes */
+	if (jiffies % (120 * HZ) == 0 && time_after(jiffies, lasttime)) {
+		printk(KERN_CRIT "Timer: Excesssive Atomic allocs\n");
+		/* Force memory to become exhausted */
+		base = kzalloc(NR_TEST * sizeof(void *), GFP_ATOMIC);
+
+		for (i = 0; i < NR_TEST; i++) {
+			base[i] = alloc_page(GFP_ATOMIC);
+			if (!base[i]) {
+				printk("Alloc failed at %d\n", i);
+				break;
+			}
+		}
+		for (i = 0; i < NR_TEST; i++)
+			if (base[i])
+				put_page(base[i]);
+		kfree(base);
+		printk(KERN_CRIT "Timer: Memory freed\n");
+		lasttime = jiffies;
+	}
 }
 
 /*