1 files changed, 79 insertions, 0 deletions
diff --git a/mm/thrash.c b/mm/thrash.c
new file mode 100644
index 0000000..c4c5205
--- /dev/null
+++ b/mm/thrash.c
@@ -0,0 +1,79 @@
+/*
+ * mm/thrash.c
+ *
+ * Copyright (C) 2004, Red Hat, Inc.
+ * Copyright (C) 2004, Rik van Riel <riel@redhat.com>
+ * Released under the GPL, see the file COPYING for details.
+ *
+ * Simple token based thrashing protection, using the algorithm
+ * described in:  http://www.cs.wm.edu/~sjiang/token.pdf
+ *
+ * Sep 2006, Ashwin Chaugule <ashwin.chaugule@celunite.com>
+ * Improved algorithm to pass token:
+ * Each task has a priority which is incremented if it contended
+ * for the token in an interval less than its previous attempt.
+ * If the token is acquired, that task's priority is boosted to prevent
+ * the token from bouncing around too often and to let the task make
+ * some progress in its execution.
+ */
+
+#include <linux/jiffies.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/swap.h>
+
+static DEFINE_SPINLOCK(swap_token_lock);
+struct mm_struct *swap_token_mm;
+static unsigned int global_faults;
+
+void grab_swap_token(void)
+{
+	int current_interval;
+
+	global_faults++;
+
+	current_interval = global_faults - current->mm->faultstamp;
+
+	if (!spin_trylock(&swap_token_lock))
+		return;
+
+	/* First come first served */
+	if (swap_token_mm == NULL) {
+		current->mm->token_priority = current->mm->token_priority + 2;
+		swap_token_mm = current->mm;
+		goto out;
+	}
+
+	if (current->mm != swap_token_mm) {
+		if (current_interval < current->mm->last_interval)
+			current->mm->token_priority++;
+		else {
+			if (likely(current->mm->token_priority > 0))
+				current->mm->token_priority--;
+		}
+		/* Check if we deserve the token */
+		if (current->mm->token_priority >
+				swap_token_mm->token_priority) {
+			current->mm->token_priority += 2;
+			swap_token_mm = current->mm;
+		}
+	} else {
+		/* Token holder came in again! */
+		current->mm->token_priority += 2;
+	}
+
+out:
+	current->mm->faultstamp = global_faults;
+	current->mm->last_interval = current_interval;
+	spin_unlock(&swap_token_lock);
+return;
+}
+
+/* Called on process exit. */
+void __put_swap_token(struct mm_struct *mm)
+{
+	spin_lock(&swap_token_lock);
+	if (likely(mm == swap_token_mm))
+		swap_token_mm = NULL;
+	spin_unlock(&swap_token_lock);
+}