/* * 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);}