FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_zeroidle.c

     /*-
      * Copyright (c) 1994 John Dyson
      * Copyright (c) 2001 Matt Dillon
      *
      * All rights reserved.  Terms for use and redistribution
      * are covered by the BSD Copyright as found in /usr/src/COPYRIGHT.
      *
      *      from: @(#)vm_machdep.c  7.3 (Berkeley) 5/13/91
      *      Utah $Hdr: vm_machdep.c 1.16.1.1 89/06/23$
     * $FreeBSD: releng/5.0/sys/vm/vm_zeroidle.c 104964 2002-10-12 05:32:24Z jeff $
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/proc.h>
    #include <sys/resourcevar.h>
    #include <sys/vmmeter.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/sched.h>
    #include <sys/sysctl.h>
    #include <sys/kthread.h>
    
    #include <vm/vm.h>
    #include <vm/vm_page.h>
    
    SYSCTL_DECL(_vm_stats_misc);
    
    static int cnt_prezero;
    SYSCTL_INT(_vm_stats_misc, OID_AUTO,
            cnt_prezero, CTLFLAG_RD, &cnt_prezero, 0, "");
    
    static int idlezero_enable = 1;
    SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &idlezero_enable, 0, "");
    TUNABLE_INT("vm.idlezero_enable", &idlezero_enable);
    
    static int idlezero_maxrun = 16;
    SYSCTL_INT(_vm, OID_AUTO, idlezero_maxrun, CTLFLAG_RW, &idlezero_maxrun, 0, "");
    TUNABLE_INT("vm.idlezero_maxrun", &idlezero_maxrun);
    
    /*
     * Implement the pre-zeroed page mechanism.
     */
    
    #define ZIDLE_LO(v)     ((v) * 2 / 3)
    #define ZIDLE_HI(v)     ((v) * 4 / 5)
    
    static int zero_state;
    
    static int
    vm_page_zero_check(void)
    {
    
            if (!idlezero_enable)
                    return 0;
            /*
             * Attempt to maintain approximately 1/2 of our free pages in a
             * PG_ZERO'd state.   Add some hysteresis to (attempt to) avoid
             * generally zeroing a page when the system is near steady-state.
             * Otherwise we might get 'flutter' during disk I/O / IPC or 
             * fast sleeps.  We also do not want to be continuously zeroing
             * pages because doing so may flush our L1 and L2 caches too much.
             */
            if (zero_state && vm_page_zero_count >= ZIDLE_LO(cnt.v_free_count))
                    return 0;
            if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
                    return 0;
            return 1;
    }
    
    static int
    vm_page_zero_idle(void)
    {
            static int free_rover;
            vm_page_t m;
    
            mtx_lock_spin(&vm_page_queue_free_mtx);
            zero_state = 0;
            m = vm_pageq_find(PQ_FREE, free_rover, FALSE);
            if (m != NULL && (m->flags & PG_ZERO) == 0) {
                    vm_pageq_remove_nowakeup(m);
                    mtx_unlock_spin(&vm_page_queue_free_mtx);
                    pmap_zero_page_idle(m);
                    mtx_lock_spin(&vm_page_queue_free_mtx);
                    m->flags |= PG_ZERO;
                    vm_pageq_enqueue(PQ_FREE + m->pc, m);
                    ++vm_page_zero_count;
                    ++cnt_prezero;
                    if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
                            zero_state = 1;
            }
            free_rover = (free_rover + PQ_PRIME2) & PQ_L2_MASK;
            mtx_unlock_spin(&vm_page_queue_free_mtx);
            return 1;
    }
    
    
    /* Called by vm_page_free to hint that a new page is available */
   void
   vm_page_zero_idle_wakeup(void)
   {
   
           if (idlezero_enable && vm_page_zero_check())
                   wakeup(&zero_state);
   }
   
   static void
   vm_pagezero(void)
   {
           struct thread *td;
           struct proc *p;
           struct rtprio rtp;
           int pages = 0;
           int pri;
   
           td = curthread;
           p = td->td_proc;
           rtp.prio = RTP_PRIO_MAX;
           rtp.type = RTP_PRIO_IDLE;
           mtx_lock_spin(&sched_lock);
           rtp_to_pri(&rtp, td->td_ksegrp);
           pri = td->td_priority;
           mtx_unlock_spin(&sched_lock);
           PROC_LOCK(p);
           p->p_flag |= P_NOLOAD;
           PROC_UNLOCK(p);
   
           for (;;) {
                   if (vm_page_zero_check()) {
                           pages += vm_page_zero_idle();
                           if (pages > idlezero_maxrun || sched_runnable()) {
                                   mtx_lock_spin(&sched_lock);
                                   td->td_proc->p_stats->p_ru.ru_nvcsw++;
                                   mi_switch();
                                   mtx_unlock_spin(&sched_lock);
                                   pages = 0;
                           }
                   } else {
                           tsleep(&zero_state, pri, "pgzero", hz * 300);
                           pages = 0;
                   }
           }
   }
   
   static struct proc *pagezero;
   static struct kproc_desc pagezero_kp = {
            "pagezero",
            vm_pagezero,
            &pagezero
   };
   SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start, &pagezero_kp)

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