/* * 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); }