The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*-
    2  * Copyright (c) 1994 John Dyson
    3  * Copyright (c) 2001 Matt Dillon
    4  *
    5  * All Rights Reserved.
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice, this list of conditions and the following disclaimer.
   11  * 2. Redistributions in binary form must reproduce the above copyright
   12  *    notice, this list of conditions and the following disclaimer in the
   13  *    documentation and/or other materials provided with the distribution.
   14  * 4. Neither the name of the University nor the names of its contributors
   15  *    may be used to endorse or promote products derived from this software
   16  *    without specific prior written permission.
   17  *
   18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
   19  * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
   20  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
   22  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
   24  * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   25  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   26  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   27  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   28  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   29  *
   30  *      from: @(#)vm_machdep.c  7.3 (Berkeley) 5/13/91
   31  *      Utah $Hdr: vm_machdep.c 1.16.1.1 89/06/23$
   32  * from: FreeBSD: .../i386/vm_machdep.c,v 1.165 2001/07/04 23:27:04 dillon
   33  */
   34 
   35 #include <sys/cdefs.h>
   36 __FBSDID("$FreeBSD$");
   37 
   38 #include <opt_sched.h>
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/kernel.h>
   43 #include <sys/proc.h>
   44 #include <sys/vmmeter.h>
   45 #include <sys/lock.h>
   46 #include <sys/mutex.h>
   47 #include <sys/sched.h>
   48 #include <sys/sysctl.h>
   49 #include <sys/kthread.h>
   50 #include <sys/unistd.h>
   51 
   52 #include <vm/vm.h>
   53 #include <vm/vm_page.h>
   54 #include <vm/vm_phys.h>
   55 
   56 static int idlezero_enable_default = 0;
   57 TUNABLE_INT("vm.idlezero_enable", &idlezero_enable_default);
   58 /* Defer setting the enable flag until the kthread is running. */
   59 static int idlezero_enable = 0;
   60 SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &idlezero_enable, 0,
   61     "Allow the kernel to use idle cpu cycles to zero-out pages");
   62 /*
   63  * Implement the pre-zeroed page mechanism.
   64  */
   65 
   66 #define ZIDLE_LO(v)     ((v) * 2 / 3)
   67 #define ZIDLE_HI(v)     ((v) * 4 / 5)
   68 
   69 static boolean_t wakeup_needed = FALSE;
   70 static int zero_state;
   71 
   72 static int
   73 vm_page_zero_check(void)
   74 {
   75 
   76         if (!idlezero_enable)
   77                 return (0);
   78         /*
   79          * Attempt to maintain approximately 1/2 of our free pages in a
   80          * PG_ZERO'd state.   Add some hysteresis to (attempt to) avoid
   81          * generally zeroing a page when the system is near steady-state.
   82          * Otherwise we might get 'flutter' during disk I/O / IPC or 
   83          * fast sleeps.  We also do not want to be continuously zeroing
   84          * pages because doing so may flush our L1 and L2 caches too much.
   85          */
   86         if (zero_state && vm_page_zero_count >= ZIDLE_LO(cnt.v_free_count))
   87                 return (0);
   88         if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
   89                 return (0);
   90         return (1);
   91 }
   92 
   93 static void
   94 vm_page_zero_idle(void)
   95 {
   96 
   97         mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
   98         zero_state = 0;
   99         if (vm_phys_zero_pages_idle()) {
  100                 if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
  101                         zero_state = 1;
  102         }
  103 }
  104 
  105 /* Called by vm_page_free to hint that a new page is available. */
  106 void
  107 vm_page_zero_idle_wakeup(void)
  108 {
  109 
  110         mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
  111         if (wakeup_needed && vm_page_zero_check()) {
  112                 wakeup_needed = FALSE;
  113                 wakeup(&zero_state);
  114         }
  115 }
  116 
  117 static void
  118 vm_pagezero(void __unused *arg)
  119 {
  120 
  121         idlezero_enable = idlezero_enable_default;
  122 
  123         mtx_lock(&vm_page_queue_free_mtx);
  124         for (;;) {
  125                 if (vm_page_zero_check()) {
  126                         vm_page_zero_idle();
  127 #ifndef PREEMPTION
  128                         if (sched_runnable()) {
  129                                 thread_lock(curthread);
  130                                 mi_switch(SW_VOL | SWT_IDLE, NULL);
  131                                 thread_unlock(curthread);
  132                         }
  133 #endif
  134                 } else {
  135                         wakeup_needed = TRUE;
  136                         msleep(&zero_state, &vm_page_queue_free_mtx, 0,
  137                             "pgzero", hz * 300);
  138                 }
  139         }
  140 }
  141 
  142 static void
  143 pagezero_start(void __unused *arg)
  144 {
  145         int error;
  146         struct proc *p;
  147         struct thread *td;
  148 
  149         error = kproc_create(vm_pagezero, NULL, &p, RFSTOPPED, 0, "pagezero");
  150         if (error)
  151                 panic("pagezero_start: error %d\n", error);
  152         td = FIRST_THREAD_IN_PROC(p);
  153         thread_lock(td);
  154 
  155         /* We're an idle task, don't count us in the load. */
  156         td->td_flags |= TDF_NOLOAD;
  157         sched_class(td, PRI_IDLE);
  158         sched_prio(td, PRI_MAX_IDLE);
  159         sched_add(td, SRQ_BORING);
  160         thread_unlock(td);
  161 }
  162 SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, pagezero_start, NULL);

Cache object: 397f88f95fa3a3fb732e9824d0c6ba29


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