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

     /*-
      * Copyright (c) 1991, 1993
      *      The Regents of the University of California.  All rights reserved.
      *
      * This code is derived from software contributed to Berkeley by
      * The Mach Operating System project at Carnegie-Mellon University.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      from: @(#)vm_glue.c     8.6 (Berkeley) 1/5/94
     *
     *
     * Copyright (c) 1987, 1990 Carnegie-Mellon University.
     * All rights reserved.
     *
     * Permission to use, copy, modify and distribute this software and
     * its documentation is hereby granted, provided that both the copyright
     * notice and this permission notice appear in all copies of the
     * software, derivative works or modified versions, and any portions
     * thereof, and that both notices appear in supporting documentation.
     *
     * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
     * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
     * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
     *
     * Carnegie Mellon requests users of this software to return to
     *
     *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
     *  School of Computer Science
     *  Carnegie Mellon University
     *  Pittsburgh PA 15213-3890
     *
     * any improvements or extensions that they make and grant Carnegie the
     * rights to redistribute these changes.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/7.4/sys/vm/vm_glue.c 182976 2008-09-12 21:00:11Z jhb $");
    
    #include "opt_vm.h"
    #include "opt_kstack_pages.h"
    #include "opt_kstack_max_pages.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/limits.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/proc.h>
    #include <sys/resourcevar.h>
    #include <sys/sched.h>
    #include <sys/sf_buf.h>
    #include <sys/shm.h>
    #include <sys/vmmeter.h>
    #include <sys/sx.h>
    #include <sys/sysctl.h>
    
    #include <sys/kernel.h>
    #include <sys/ktr.h>
    #include <sys/unistd.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/pmap.h>
    #include <vm/vm_map.h>
    #include <vm/vm_page.h>
    #include <vm/vm_pageout.h>
    #include <vm/vm_object.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_pager.h>
    #include <vm/swap_pager.h>
    
    extern int maxslp;
    
    /*
     * System initialization
    *
    * Note: proc0 from proc.h
    */
   static void vm_init_limits(void *);
   SYSINIT(vm_limits, SI_SUB_VM_CONF, SI_ORDER_FIRST, vm_init_limits, &proc0);
   
   /*
    * THIS MUST BE THE LAST INITIALIZATION ITEM!!!
    *
    * Note: run scheduling should be divorced from the vm system.
    */
   static void scheduler(void *);
   SYSINIT(scheduler, SI_SUB_RUN_SCHEDULER, SI_ORDER_ANY, scheduler, NULL);
   
   #ifndef NO_SWAPPING
   static int swapout(struct proc *);
   static void swapclear(struct proc *);
   #endif
   
   /*
    * MPSAFE
    *
    * WARNING!  This code calls vm_map_check_protection() which only checks
    * the associated vm_map_entry range.  It does not determine whether the
    * contents of the memory is actually readable or writable.  In most cases
    * just checking the vm_map_entry is sufficient within the kernel's address
    * space.
    */
   int
   kernacc(addr, len, rw)
           void *addr;
           int len, rw;
   {
           boolean_t rv;
           vm_offset_t saddr, eaddr;
           vm_prot_t prot;
   
           KASSERT((rw & ~VM_PROT_ALL) == 0,
               ("illegal ``rw'' argument to kernacc (%x)\n", rw));
   
           if ((vm_offset_t)addr + len > kernel_map->max_offset ||
               (vm_offset_t)addr + len < (vm_offset_t)addr)
                   return (FALSE);
   
           prot = rw;
           saddr = trunc_page((vm_offset_t)addr);
           eaddr = round_page((vm_offset_t)addr + len);
           vm_map_lock_read(kernel_map);
           rv = vm_map_check_protection(kernel_map, saddr, eaddr, prot);
           vm_map_unlock_read(kernel_map);
           return (rv == TRUE);
   }
   
   /*
    * MPSAFE
    *
    * WARNING!  This code calls vm_map_check_protection() which only checks
    * the associated vm_map_entry range.  It does not determine whether the
    * contents of the memory is actually readable or writable.  vmapbuf(),
    * vm_fault_quick(), or copyin()/copout()/su*()/fu*() functions should be
    * used in conjuction with this call.
    */
   int
   useracc(addr, len, rw)
           void *addr;
           int len, rw;
   {
           boolean_t rv;
           vm_prot_t prot;
           vm_map_t map;
   
           KASSERT((rw & ~VM_PROT_ALL) == 0,
               ("illegal ``rw'' argument to useracc (%x)\n", rw));
           prot = rw;
           map = &curproc->p_vmspace->vm_map;
           if ((vm_offset_t)addr + len > vm_map_max(map) ||
               (vm_offset_t)addr + len < (vm_offset_t)addr) {
                   return (FALSE);
           }
           vm_map_lock_read(map);
           rv = vm_map_check_protection(map, trunc_page((vm_offset_t)addr),
               round_page((vm_offset_t)addr + len), prot);
           vm_map_unlock_read(map);
           return (rv == TRUE);
   }
   
   int
   vslock(void *addr, size_t len)
   {
           vm_offset_t end, last, start;
           vm_size_t npages;
           int error;
   
           last = (vm_offset_t)addr + len;
           start = trunc_page((vm_offset_t)addr);
           end = round_page(last);
           if (last < (vm_offset_t)addr || end < (vm_offset_t)addr)
                   return (EINVAL);
           npages = atop(end - start);
           if (npages > vm_page_max_wired)
                   return (ENOMEM);
           PROC_LOCK(curproc);
           if (ptoa(npages +
               pmap_wired_count(vm_map_pmap(&curproc->p_vmspace->vm_map))) >
               lim_cur(curproc, RLIMIT_MEMLOCK)) {
                   PROC_UNLOCK(curproc);
                   return (ENOMEM);
           }
           PROC_UNLOCK(curproc);
   #if 0
           /*
            * XXX - not yet
            *
            * The limit for transient usage of wired pages should be
            * larger than for "permanent" wired pages (mlock()).
            *
            * Also, the sysctl code, which is the only present user
            * of vslock(), does a hard loop on EAGAIN.
            */
           if (npages + cnt.v_wire_count > vm_page_max_wired)
                   return (EAGAIN);
   #endif
           error = vm_map_wire(&curproc->p_vmspace->vm_map, start, end,
               VM_MAP_WIRE_SYSTEM | VM_MAP_WIRE_NOHOLES);
           /*
            * Return EFAULT on error to match copy{in,out}() behaviour
            * rather than returning ENOMEM like mlock() would.
            */
           return (error == KERN_SUCCESS ? 0 : EFAULT);
   }
   
   void
   vsunlock(void *addr, size_t len)
   {
   
           /* Rely on the parameter sanity checks performed by vslock(). */
           (void)vm_map_unwire(&curproc->p_vmspace->vm_map,
               trunc_page((vm_offset_t)addr), round_page((vm_offset_t)addr + len),
               VM_MAP_WIRE_SYSTEM | VM_MAP_WIRE_NOHOLES);
   }
   
   /*
    * Pin the page contained within the given object at the given offset.  If the
    * page is not resident, allocate and load it using the given object's pager.
    * Return the pinned page if successful; otherwise, return NULL.
    */
   static vm_page_t
   vm_imgact_hold_page(vm_object_t object, vm_ooffset_t offset)
   {
           vm_page_t m, ma[1];
           vm_pindex_t pindex;
           int rv;
   
           VM_OBJECT_LOCK(object);
           pindex = OFF_TO_IDX(offset);
           m = vm_page_grab(object, pindex, VM_ALLOC_NORMAL | VM_ALLOC_RETRY);
           if ((m->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) {
                   ma[0] = m;
                   rv = vm_pager_get_pages(object, ma, 1, 0);
                   m = vm_page_lookup(object, pindex);
                   if (m == NULL)
                           goto out;
                   if (m->valid == 0 || rv != VM_PAGER_OK) {
                           vm_page_lock_queues();
                           vm_page_free(m);
                           vm_page_unlock_queues();
                           m = NULL;
                           goto out;
                   }
           }
           vm_page_lock_queues();
           vm_page_hold(m);
           vm_page_unlock_queues();
           vm_page_wakeup(m);
   out:
           VM_OBJECT_UNLOCK(object);
           return (m);
   }
   
   /*
    * Return a CPU private mapping to the page at the given offset within the
    * given object.  The page is pinned before it is mapped.
    */
   struct sf_buf *
   vm_imgact_map_page(vm_object_t object, vm_ooffset_t offset)
   {
           vm_page_t m;
   
           m = vm_imgact_hold_page(object, offset);
           if (m == NULL)
                   return (NULL);
           sched_pin();
           return (sf_buf_alloc(m, SFB_CPUPRIVATE));
   }
   
   /*
    * Destroy the given CPU private mapping and unpin the page that it mapped.
    */
   void
   vm_imgact_unmap_page(struct sf_buf *sf)
   {
           vm_page_t m;
   
           m = sf_buf_page(sf);
           sf_buf_free(sf);
           sched_unpin();
           vm_page_lock_queues();
           vm_page_unhold(m);
           vm_page_unlock_queues();
   }
   
   #ifndef KSTACK_MAX_PAGES
   #define KSTACK_MAX_PAGES 32
   #endif
   
   /*
    * Create the kernel stack (including pcb for i386) for a new thread.
    * This routine directly affects the fork perf for a process and
    * create performance for a thread.
    */
   int
   vm_thread_new(struct thread *td, int pages)
   {
           vm_object_t ksobj;
           vm_offset_t ks;
           vm_page_t m, ma[KSTACK_MAX_PAGES];
           int i;
   
           /* Bounds check */
           if (pages <= 1)
                   pages = KSTACK_PAGES;
           else if (pages > KSTACK_MAX_PAGES)
                   pages = KSTACK_MAX_PAGES;
           /*
            * Allocate an object for the kstack.
            */
           ksobj = vm_object_allocate(OBJT_DEFAULT, pages);
           /*
            * Get a kernel virtual address for this thread's kstack.
            */
           ks = kmem_alloc_nofault(kernel_map,
              (pages + KSTACK_GUARD_PAGES) * PAGE_SIZE);
           if (ks == 0) {
                   printf("vm_thread_new: kstack allocation failed\n");
                   vm_object_deallocate(ksobj);
                   return (0);
           }
           
           if (KSTACK_GUARD_PAGES != 0) {
                   pmap_qremove(ks, KSTACK_GUARD_PAGES);
                   ks += KSTACK_GUARD_PAGES * PAGE_SIZE;
           }
           td->td_kstack_obj = ksobj;
           td->td_kstack = ks;
           /*
            * Knowing the number of pages allocated is useful when you
            * want to deallocate them.
            */
           td->td_kstack_pages = pages;
           /* 
            * For the length of the stack, link in a real page of ram for each
            * page of stack.
            */
           VM_OBJECT_LOCK(ksobj);
           for (i = 0; i < pages; i++) {
                   /*
                    * Get a kernel stack page.
                    */
                   m = vm_page_grab(ksobj, i, VM_ALLOC_NOBUSY |
                       VM_ALLOC_NORMAL | VM_ALLOC_RETRY | VM_ALLOC_WIRED);
                   ma[i] = m;
                   m->valid = VM_PAGE_BITS_ALL;
           }
           VM_OBJECT_UNLOCK(ksobj);
           pmap_qenter(ks, ma, pages);
           return (1);
   }
   
   /*
    * Dispose of a thread's kernel stack.
    */
   void
   vm_thread_dispose(struct thread *td)
   {
           vm_object_t ksobj;
           vm_offset_t ks;
           vm_page_t m;
           int i, pages;
   
           pages = td->td_kstack_pages;
           ksobj = td->td_kstack_obj;
           ks = td->td_kstack;
           pmap_qremove(ks, pages);
           VM_OBJECT_LOCK(ksobj);
           for (i = 0; i < pages; i++) {
                   m = vm_page_lookup(ksobj, i);
                   if (m == NULL)
                           panic("vm_thread_dispose: kstack already missing?");
                   vm_page_lock_queues();
                   vm_page_unwire(m, 0);
                   vm_page_free(m);
                   vm_page_unlock_queues();
           }
           VM_OBJECT_UNLOCK(ksobj);
           vm_object_deallocate(ksobj);
           kmem_free(kernel_map, ks - (KSTACK_GUARD_PAGES * PAGE_SIZE),
               (pages + KSTACK_GUARD_PAGES) * PAGE_SIZE);
           td->td_kstack = 0;
   }
   
   /*
    * Allow a thread's kernel stack to be paged out.
    */
   void
   vm_thread_swapout(struct thread *td)
   {
           vm_object_t ksobj;
           vm_page_t m;
           int i, pages;
   
           cpu_thread_swapout(td);
           pages = td->td_kstack_pages;
           ksobj = td->td_kstack_obj;
           pmap_qremove(td->td_kstack, pages);
           VM_OBJECT_LOCK(ksobj);
           for (i = 0; i < pages; i++) {
                   m = vm_page_lookup(ksobj, i);
                   if (m == NULL)
                           panic("vm_thread_swapout: kstack already missing?");
                   vm_page_lock_queues();
                   vm_page_dirty(m);
                   vm_page_unwire(m, 0);
                   vm_page_unlock_queues();
           }
           VM_OBJECT_UNLOCK(ksobj);
   }
   
   /*
    * Bring the kernel stack for a specified thread back in.
    */
   void
   vm_thread_swapin(struct thread *td)
   {
           vm_object_t ksobj;
           vm_page_t m, ma[KSTACK_MAX_PAGES];
           int i, pages, rv;
   
           pages = td->td_kstack_pages;
           ksobj = td->td_kstack_obj;
           VM_OBJECT_LOCK(ksobj);
           for (i = 0; i < pages; i++) {
                   m = vm_page_grab(ksobj, i, VM_ALLOC_NORMAL | VM_ALLOC_RETRY);
                   if (m->valid != VM_PAGE_BITS_ALL) {
                           rv = vm_pager_get_pages(ksobj, &m, 1, 0);
                           if (rv != VM_PAGER_OK)
                                   panic("vm_thread_swapin: cannot get kstack for proc: %d", td->td_proc->p_pid);
                           m = vm_page_lookup(ksobj, i);
                           m->valid = VM_PAGE_BITS_ALL;
                   }
                   ma[i] = m;
                   vm_page_lock_queues();
                   vm_page_wire(m);
                   vm_page_unlock_queues();
                   vm_page_wakeup(m);
           }
           VM_OBJECT_UNLOCK(ksobj);
           pmap_qenter(td->td_kstack, ma, pages);
           cpu_thread_swapin(td);
   }
   
   /*
    * Set up a variable-sized alternate kstack.
    */
   int
   vm_thread_new_altkstack(struct thread *td, int pages)
   {
   
           td->td_altkstack = td->td_kstack;
           td->td_altkstack_obj = td->td_kstack_obj;
           td->td_altkstack_pages = td->td_kstack_pages;
   
           return (vm_thread_new(td, pages));
   }
   
   /*
    * Restore the original kstack.
    */
   void
   vm_thread_dispose_altkstack(struct thread *td)
   {
   
           vm_thread_dispose(td);
   
           td->td_kstack = td->td_altkstack;
           td->td_kstack_obj = td->td_altkstack_obj;
           td->td_kstack_pages = td->td_altkstack_pages;
           td->td_altkstack = 0;
           td->td_altkstack_obj = NULL;
           td->td_altkstack_pages = 0;
   }
   
   /*
    * Implement fork's actions on an address space.
    * Here we arrange for the address space to be copied or referenced,
    * allocate a user struct (pcb and kernel stack), then call the
    * machine-dependent layer to fill those in and make the new process
    * ready to run.  The new process is set up so that it returns directly
    * to user mode to avoid stack copying and relocation problems.
    */
   int
   vm_forkproc(td, p2, td2, vm2, flags)
           struct thread *td;
           struct proc *p2;
           struct thread *td2;
           struct vmspace *vm2;
           int flags;
   {
           struct proc *p1 = td->td_proc;
           int error;
   
           if ((flags & RFPROC) == 0) {
                   /*
                    * Divorce the memory, if it is shared, essentially
                    * this changes shared memory amongst threads, into
                    * COW locally.
                    */
                   if ((flags & RFMEM) == 0) {
                           if (p1->p_vmspace->vm_refcnt > 1) {
                                   error = vmspace_unshare(p1);
                                   if (error)
                                           return (error);
                           }
                   }
                   cpu_fork(td, p2, td2, flags);
                   return (0);
           }
   
           if (flags & RFMEM) {
                   p2->p_vmspace = p1->p_vmspace;
                   atomic_add_int(&p1->p_vmspace->vm_refcnt, 1);
           }
   
           while (vm_page_count_severe()) {
                   VM_WAIT;
           }
   
           if ((flags & RFMEM) == 0) {
                   p2->p_vmspace = vm2;
                   if (p1->p_vmspace->vm_shm)
                           shmfork(p1, p2);
           }
   
           /*
            * cpu_fork will copy and update the pcb, set up the kernel stack,
            * and make the child ready to run.
            */
           cpu_fork(td, p2, td2, flags);
           return (0);
   }
   
   /*
    * Called after process has been wait(2)'ed apon and is being reaped.
    * The idea is to reclaim resources that we could not reclaim while
    * the process was still executing.
    */
   void
   vm_waitproc(p)
           struct proc *p;
   {
   
           vmspace_exitfree(p);            /* and clean-out the vmspace */
   }
   
   /*
    * Set default limits for VM system.
    * Called for proc 0, and then inherited by all others.
    *
    * XXX should probably act directly on proc0.
    */
   static void
   vm_init_limits(udata)
           void *udata;
   {
           struct proc *p = udata;
           struct plimit *limp;
           int rss_limit;
   
           /*
            * Set up the initial limits on process VM. Set the maximum resident
            * set size to be half of (reasonably) available memory.  Since this
            * is a soft limit, it comes into effect only when the system is out
            * of memory - half of main memory helps to favor smaller processes,
            * and reduces thrashing of the object cache.
            */
           limp = p->p_limit;
           limp->pl_rlimit[RLIMIT_STACK].rlim_cur = dflssiz;
           limp->pl_rlimit[RLIMIT_STACK].rlim_max = maxssiz;
           limp->pl_rlimit[RLIMIT_DATA].rlim_cur = dfldsiz;
           limp->pl_rlimit[RLIMIT_DATA].rlim_max = maxdsiz;
           /* limit the limit to no less than 2MB */
           rss_limit = max(cnt.v_free_count, 512);
           limp->pl_rlimit[RLIMIT_RSS].rlim_cur = ptoa(rss_limit);
           limp->pl_rlimit[RLIMIT_RSS].rlim_max = RLIM_INFINITY;
   }
   
   void
   faultin(p)
           struct proc *p;
   {
   #ifdef NO_SWAPPING
   
           PROC_LOCK_ASSERT(p, MA_OWNED);
           if ((p->p_flag & P_INMEM) == 0)
                   panic("faultin: proc swapped out with NO_SWAPPING!");
   #else /* !NO_SWAPPING */
           struct thread *td;
   
           PROC_LOCK_ASSERT(p, MA_OWNED);
           /*
            * If another process is swapping in this process,
            * just wait until it finishes.
            */
           if (p->p_flag & P_SWAPPINGIN) {
                   while (p->p_flag & P_SWAPPINGIN)
                           msleep(&p->p_flag, &p->p_mtx, PVM, "faultin", 0);
                   return;
           }
           if ((p->p_flag & P_INMEM) == 0) {
                   /*
                    * Don't let another thread swap process p out while we are
                    * busy swapping it in.
                    */
                   ++p->p_lock;
                   p->p_flag |= P_SWAPPINGIN;
                   PROC_UNLOCK(p);
   
                   /*
                    * We hold no lock here because the list of threads
                    * can not change while all threads in the process are
                    * swapped out.
                    */
                   FOREACH_THREAD_IN_PROC(p, td)
                           vm_thread_swapin(td);
                   PROC_LOCK(p);
                   PROC_SLOCK(p);
                   swapclear(p);
                   p->p_swtick = ticks;
                   PROC_SUNLOCK(p);
   
                   wakeup(&p->p_flag);
   
                   /* Allow other threads to swap p out now. */
                   --p->p_lock;
           }
   #endif /* NO_SWAPPING */
   }
   
   /*
    * This swapin algorithm attempts to swap-in processes only if there
    * is enough space for them.  Of course, if a process waits for a long
    * time, it will be swapped in anyway.
    *
    *  XXXKSE - process with the thread with highest priority counts..
    *
    * Giant is held on entry.
    */
   /* ARGSUSED*/
   static void
   scheduler(dummy)
           void *dummy;
   {
           struct proc *p;
           struct thread *td;
           struct proc *pp;
           int slptime;
           int swtime;
           int ppri;
           int pri;
   
           mtx_assert(&Giant, MA_OWNED | MA_NOTRECURSED);
           mtx_unlock(&Giant);
   
   loop:
           if (vm_page_count_min()) {
                   VM_WAIT;
                   goto loop;
           }
   
           pp = NULL;
           ppri = INT_MIN;
           sx_slock(&allproc_lock);
           FOREACH_PROC_IN_SYSTEM(p) {
                   PROC_LOCK(p);
                   if (p->p_flag & (P_SWAPPINGOUT | P_SWAPPINGIN | P_INMEM)) {
                           PROC_UNLOCK(p);
                           continue;
                   }
                   swtime = (ticks - p->p_swtick) / hz;
                   PROC_SLOCK(p);
                   FOREACH_THREAD_IN_PROC(p, td) {
                           /*
                            * An otherwise runnable thread of a process
                            * swapped out has only the TDI_SWAPPED bit set.
                            * 
                            */
                           thread_lock(td);
                           if (td->td_inhibitors == TDI_SWAPPED) {
                                   slptime = (ticks - td->td_slptick) / hz;
                                   pri = swtime + slptime;
                                   if ((td->td_flags & TDF_SWAPINREQ) == 0)
                                           pri -= p->p_nice * 8;
                                   /*
                                    * if this thread is higher priority
                                    * and there is enough space, then select
                                    * this process instead of the previous
                                    * selection.
                                    */
                                   if (pri > ppri) {
                                           pp = p;
                                           ppri = pri;
                                   }
                           }
                           thread_unlock(td);
                   }
                   PROC_SUNLOCK(p);
                   PROC_UNLOCK(p);
           }
           sx_sunlock(&allproc_lock);
   
           /*
            * Nothing to do, back to sleep.
            */
           if ((p = pp) == NULL) {
                   tsleep(&proc0, PVM, "sched", maxslp * hz / 2);
                   goto loop;
           }
           PROC_LOCK(p);
   
           /*
            * Another process may be bringing or may have already
            * brought this process in while we traverse all threads.
            * Or, this process may even be being swapped out again.
            */
           if (p->p_flag & (P_INMEM | P_SWAPPINGOUT | P_SWAPPINGIN)) {
                   PROC_UNLOCK(p);
                   goto loop;
           }
   
           /*
            * We would like to bring someone in. (only if there is space).
            * [What checks the space? ]
            */
           faultin(p);
           PROC_UNLOCK(p);
           goto loop;
   }
   
   void
   kick_proc0(void)
   {
   
           wakeup(&proc0);
   }
   
   #ifndef NO_SWAPPING
   
   /*
    * Swap_idle_threshold1 is the guaranteed swapped in time for a process
    */
   static int swap_idle_threshold1 = 2;
   SYSCTL_INT(_vm, OID_AUTO, swap_idle_threshold1, CTLFLAG_RW,
       &swap_idle_threshold1, 0, "Guaranteed swapped in time for a process");
   
   /*
    * Swap_idle_threshold2 is the time that a process can be idle before
    * it will be swapped out, if idle swapping is enabled.
    */
   static int swap_idle_threshold2 = 10;
   SYSCTL_INT(_vm, OID_AUTO, swap_idle_threshold2, CTLFLAG_RW,
       &swap_idle_threshold2, 0, "Time before a process will be swapped out");
   
   /*
    * Swapout is driven by the pageout daemon.  Very simple, we find eligible
    * procs and swap out their stacks.  We try to always "swap" at least one
    * process in case we need the room for a swapin.
    * If any procs have been sleeping/stopped for at least maxslp seconds,
    * they are swapped.  Else, we swap the longest-sleeping or stopped process,
    * if any, otherwise the longest-resident process.
    */
   void
   swapout_procs(action)
   int action;
   {
           struct proc *p;
           struct thread *td;
           int didswap = 0;
   
   retry:
           sx_slock(&allproc_lock);
           FOREACH_PROC_IN_SYSTEM(p) {
                   struct vmspace *vm;
                   int minslptime = 100000;
                   int slptime;
                   
                   /*
                    * Watch out for a process in
                    * creation.  It may have no
                    * address space or lock yet.
                    */
                   if (p->p_state == PRS_NEW)
                           continue;
                   /*
                    * An aio daemon switches its
                    * address space while running.
                    * Perform a quick check whether
                    * a process has P_SYSTEM.
                    */
                   if ((p->p_flag & P_SYSTEM) != 0)
                           continue;
                   /*
                    * Do not swapout a process that
                    * is waiting for VM data
                    * structures as there is a possible
                    * deadlock.  Test this first as
                    * this may block.
                    *
                    * Lock the map until swapout
                    * finishes, or a thread of this
                    * process may attempt to alter
                    * the map.
                    */
                   vm = vmspace_acquire_ref(p);
                   if (vm == NULL)
                           continue;
                   if (!vm_map_trylock(&vm->vm_map))
                           goto nextproc1;
   
                   PROC_LOCK(p);
                   if (p->p_lock != 0 ||
                       (p->p_flag & (P_STOPPED_SINGLE|P_TRACED|P_SYSTEM|P_WEXIT)
                       ) != 0) {
                           goto nextproc2;
                   }
                   /*
                    * only aiod changes vmspace, however it will be
                    * skipped because of the if statement above checking 
                    * for P_SYSTEM
                    */
                   if ((p->p_flag & (P_INMEM|P_SWAPPINGOUT|P_SWAPPINGIN)) != P_INMEM)
                           goto nextproc2;
   
                   switch (p->p_state) {
                   default:
                           /* Don't swap out processes in any sort
                            * of 'special' state. */
                           break;
   
                   case PRS_NORMAL:
                           PROC_SLOCK(p);
                           /*
                            * do not swapout a realtime process
                            * Check all the thread groups..
                            */
                           FOREACH_THREAD_IN_PROC(p, td) {
                                   thread_lock(td);
                                   if (PRI_IS_REALTIME(td->td_pri_class)) {
                                           thread_unlock(td);
                                           goto nextproc;
                                   }
                                   slptime = (ticks - td->td_slptick) / hz;
                                   /*
                                    * Guarantee swap_idle_threshold1
                                    * time in memory.
                                    */
                                   if (slptime < swap_idle_threshold1) {
                                           thread_unlock(td);
                                           goto nextproc;
                                   }
   
                                   /*
                                    * Do not swapout a process if it is
                                    * waiting on a critical event of some
                                    * kind or there is a thread whose
                                    * pageable memory may be accessed.
                                    *
                                    * This could be refined to support
                                    * swapping out a thread.
                                    */
                                   if ((td->td_priority) < PSOCK ||
                                       !thread_safetoswapout(td)) {
                                           thread_unlock(td);
                                           goto nextproc;
                                   }
                                   /*
                                    * If the system is under memory stress,
                                    * or if we are swapping
                                    * idle processes >= swap_idle_threshold2,
                                    * then swap the process out.
                                    */
                                   if (((action & VM_SWAP_NORMAL) == 0) &&
                                       (((action & VM_SWAP_IDLE) == 0) ||
                                       (slptime < swap_idle_threshold2))) {
                                           thread_unlock(td);
                                           goto nextproc;
                                   }
   
                                   if (minslptime > slptime)
                                           minslptime = slptime;
                                   thread_unlock(td);
                           }
   
                           /*
                            * If the pageout daemon didn't free enough pages,
                            * or if this process is idle and the system is
                            * configured to swap proactively, swap it out.
                            */
                           if ((action & VM_SWAP_NORMAL) ||
                                   ((action & VM_SWAP_IDLE) &&
                                    (minslptime > swap_idle_threshold2))) {
                                   if (swapout(p) == 0)
                                           didswap++;
                                   PROC_SUNLOCK(p);
                                   PROC_UNLOCK(p);
                                   vm_map_unlock(&vm->vm_map);
                                   vmspace_free(vm);
                                   sx_sunlock(&allproc_lock);
                                   goto retry;
                           }
   nextproc:                       
                           PROC_SUNLOCK(p);
                   }
   nextproc2:
                   PROC_UNLOCK(p);
                   vm_map_unlock(&vm->vm_map);
   nextproc1:
                   vmspace_free(vm);
                   continue;
           }
           sx_sunlock(&allproc_lock);
           /*
            * If we swapped something out, and another process needed memory,
            * then wakeup the sched process.
            */
           if (didswap)
                   wakeup(&proc0);
   }
   
   static void
   swapclear(p)
           struct proc *p;
   {
           struct thread *td;
   
           PROC_LOCK_ASSERT(p, MA_OWNED);
           PROC_SLOCK_ASSERT(p, MA_OWNED);
   
           FOREACH_THREAD_IN_PROC(p, td) {
                   thread_lock(td);
                   td->td_flags |= TDF_INMEM;
                   td->td_flags &= ~TDF_SWAPINREQ;
                   TD_CLR_SWAPPED(td);
                   if (TD_CAN_RUN(td))
                           if (setrunnable(td)) {
   #ifdef INVARIANTS
                                   /*
                                    * XXX: We just cleared TDI_SWAPPED
                                    * above and set TDF_INMEM, so this
                                    * should never happen.
                                    */
                                   panic("not waking up swapper");
   #endif
                           }
                   thread_unlock(td);
           }
           p->p_flag &= ~(P_SWAPPINGIN|P_SWAPPINGOUT);
           p->p_flag |= P_INMEM;
   }
   
   static int
   swapout(p)
           struct proc *p;
   {
           struct thread *td;
   
           PROC_LOCK_ASSERT(p, MA_OWNED);
           PROC_SLOCK_ASSERT(p, MA_OWNED | MA_NOTRECURSED);
   #if defined(SWAP_DEBUG)
           printf("swapping out %d\n", p->p_pid);
   #endif
   
           /*
            * The states of this process and its threads may have changed
            * by now.  Assuming that there is only one pageout daemon thread,
            * this process should still be in memory.
            */
           KASSERT((p->p_flag & (P_INMEM|P_SWAPPINGOUT|P_SWAPPINGIN)) == P_INMEM,
                   ("swapout: lost a swapout race?"));
   
           /*
            * remember the process resident count
           */
          p->p_vmspace->vm_swrss = vmspace_resident_count(p->p_vmspace);
          /*
           * Check and mark all threads before we proceed.
           */
          p->p_flag &= ~P_INMEM;
          p->p_flag |= P_SWAPPINGOUT;
          FOREACH_THREAD_IN_PROC(p, td) {
                  thread_lock(td);
                  if (!thread_safetoswapout(td)) {
                          thread_unlock(td);
                          swapclear(p);
                          return (EBUSY);
                  }
                  td->td_flags &= ~TDF_INMEM;
                  TD_SET_SWAPPED(td);
                  thread_unlock(td);
          }
          td = FIRST_THREAD_IN_PROC(p);
          ++td->td_ru.ru_nswap;
          PROC_SUNLOCK(p);
          PROC_UNLOCK(p);
  
          /*
           * This list is stable because all threads are now prevented from
           * running.  The list is only modified in the context of a running
           * thread in this process.
           */
          FOREACH_THREAD_IN_PROC(p, td)
                  vm_thread_swapout(td);
  
          PROC_LOCK(p);
          p->p_flag &= ~P_SWAPPINGOUT;
          PROC_SLOCK(p);
          p->p_swtick = ticks;
          return (0);
  }
  #endif /* !NO_SWAPPING */

Cache object: 9fad1e33a69ad135983a25e3025e7262