FreeBSD/Linux Kernel Cross Reference
sys/uvm/uvm_glue.c

     /*      $NetBSD: uvm_glue.c,v 1.133.6.1 2009/04/01 00:25:23 snj Exp $   */
     
     /*
      * Copyright (c) 1997 Charles D. Cranor and Washington University.
      * 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.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by Charles D. Cranor,
     *      Washington University, the University of California, Berkeley and
     *      its contributors.
     * 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.
     *
     *      @(#)vm_glue.c   8.6 (Berkeley) 1/5/94
     * from: Id: uvm_glue.c,v 1.1.2.8 1998/02/07 01:16:54 chs Exp
     *
     *
     * 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>
    __KERNEL_RCSID(0, "$NetBSD: uvm_glue.c,v 1.133.6.1 2009/04/01 00:25:23 snj Exp $");
    
    #include "opt_coredump.h"
    #include "opt_kgdb.h"
    #include "opt_kstack.h"
    #include "opt_uvmhist.h"
    
    /*
     * uvm_glue.c: glue functions
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/proc.h>
    #include <sys/resourcevar.h>
    #include <sys/buf.h>
    #include <sys/user.h>
    #include <sys/syncobj.h>
    #include <sys/cpu.h>
    #include <sys/atomic.h>
    
    #include <uvm/uvm.h>
    
    /*
     * local prototypes
     */
    
    static void uvm_swapout(struct lwp *);
    static int uarea_swapin(vaddr_t);
    
   /*
    * XXXCDC: do these really belong here?
    */
   
   /*
    * uvm_kernacc: can the kernel access a region of memory
    *
    * - used only by /dev/kmem driver (mem.c)
    */
   
   bool
   uvm_kernacc(void *addr, size_t len, int rw)
   {
           bool rv;
           vaddr_t saddr, eaddr;
           vm_prot_t prot = rw == B_READ ? VM_PROT_READ : VM_PROT_WRITE;
   
           saddr = trunc_page((vaddr_t)addr);
           eaddr = round_page((vaddr_t)addr + len);
           vm_map_lock_read(kernel_map);
           rv = uvm_map_checkprot(kernel_map, saddr, eaddr, prot);
           vm_map_unlock_read(kernel_map);
   
           return(rv);
   }
   
   #ifdef KGDB
   /*
    * Change protections on kernel pages from addr to addr+len
    * (presumably so debugger can plant a breakpoint).
    *
    * We force the protection change at the pmap level.  If we were
    * to use vm_map_protect a change to allow writing would be lazily-
    * applied meaning we would still take a protection fault, something
    * we really don't want to do.  It would also fragment the kernel
    * map unnecessarily.  We cannot use pmap_protect since it also won't
    * enforce a write-enable request.  Using pmap_enter is the only way
    * we can ensure the change takes place properly.
    */
   void
   uvm_chgkprot(void *addr, size_t len, int rw)
   {
           vm_prot_t prot;
           paddr_t pa;
           vaddr_t sva, eva;
   
           prot = rw == B_READ ? VM_PROT_READ : VM_PROT_READ|VM_PROT_WRITE;
           eva = round_page((vaddr_t)addr + len);
           for (sva = trunc_page((vaddr_t)addr); sva < eva; sva += PAGE_SIZE) {
                   /*
                    * Extract physical address for the page.
                    */
                   if (pmap_extract(pmap_kernel(), sva, &pa) == false)
                           panic("%s: invalid page", __func__);
                   pmap_enter(pmap_kernel(), sva, pa, prot, PMAP_WIRED);
           }
           pmap_update(pmap_kernel());
   }
   #endif
   
   /*
    * uvm_vslock: wire user memory for I/O
    *
    * - called from physio and sys___sysctl
    * - XXXCDC: consider nuking this (or making it a macro?)
    */
   
   int
   uvm_vslock(struct vmspace *vs, void *addr, size_t len, vm_prot_t access_type)
   {
           struct vm_map *map;
           vaddr_t start, end;
           int error;
   
           map = &vs->vm_map;
           start = trunc_page((vaddr_t)addr);
           end = round_page((vaddr_t)addr + len);
           error = uvm_fault_wire(map, start, end, access_type, 0);
           return error;
   }
   
   /*
    * uvm_vsunlock: unwire user memory wired by uvm_vslock()
    *
    * - called from physio and sys___sysctl
    * - XXXCDC: consider nuking this (or making it a macro?)
    */
   
   void
   uvm_vsunlock(struct vmspace *vs, void *addr, size_t len)
   {
           uvm_fault_unwire(&vs->vm_map, trunc_page((vaddr_t)addr),
                   round_page((vaddr_t)addr + len));
   }
   
   /*
    * uvm_proc_fork: fork a virtual address space
    *
    * - the address space is copied as per parent map's inherit values
    */
   void
   uvm_proc_fork(struct proc *p1, struct proc *p2, bool shared)
   {
   
           if (shared == true) {
                   p2->p_vmspace = NULL;
                   uvmspace_share(p1, p2);
           } else {
                   p2->p_vmspace = uvmspace_fork(p1->p_vmspace);
           }
   
           cpu_proc_fork(p1, p2);
   }
   
   
   /*
    * uvm_lwp_fork: fork a thread
    *
    * - a new "user" structure is allocated for the child process
    *      [filled in by MD layer...]
    * - if specified, the child gets a new user stack described by
    *      stack and stacksize
    * - NOTE: the kernel stack may be at a different location in the child
    *      process, and thus addresses of automatic variables may be invalid
    *      after cpu_lwp_fork returns in the child process.  We do nothing here
    *      after cpu_lwp_fork returns.
    * - XXXCDC: we need a way for this to return a failure value rather
    *   than just hang
    */
   void
   uvm_lwp_fork(struct lwp *l1, struct lwp *l2, void *stack, size_t stacksize,
       void (*func)(void *), void *arg)
   {
           int error;
   
           /*
            * Wire down the U-area for the process, which contains the PCB
            * and the kernel stack.  Wired state is stored in l->l_flag's
            * L_INMEM bit rather than in the vm_map_entry's wired count
            * to prevent kernel_map fragmentation.  If we reused a cached U-area,
            * L_INMEM will already be set and we don't need to do anything.
            *
            * Note the kernel stack gets read/write accesses right off the bat.
            */
   
           if ((l2->l_flag & LW_INMEM) == 0) {
                   vaddr_t uarea = USER_TO_UAREA(l2->l_addr);
   
                   if ((error = uarea_swapin(uarea)) != 0)
                           panic("%s: uvm_fault_wire failed: %d", __func__, error);
   #ifdef PMAP_UAREA
                   /* Tell the pmap this is a u-area mapping */
                   PMAP_UAREA(uarea);
   #endif
                   l2->l_flag |= LW_INMEM;
           }
   
   #ifdef KSTACK_CHECK_MAGIC
           /*
            * fill stack with magic number
            */
           kstack_setup_magic(l2);
   #endif
   
           /*
            * cpu_lwp_fork() copy and update the pcb, and make the child ready
            * to run.  If this is a normal user fork, the child will exit
            * directly to user mode via child_return() on its first time
            * slice and will not return here.  If this is a kernel thread,
            * the specified entry point will be executed.
            */
           cpu_lwp_fork(l1, l2, stack, stacksize, func, arg);
   }
   
   static int
   uarea_swapin(vaddr_t addr)
   {
   
           return uvm_fault_wire(kernel_map, addr, addr + USPACE,
               VM_PROT_READ | VM_PROT_WRITE, 0);
   }
   
   static void
   uarea_swapout(vaddr_t addr)
   {
   
           uvm_fault_unwire(kernel_map, addr, addr + USPACE);
   }
   
   #ifndef USPACE_ALIGN
   #define USPACE_ALIGN    0
   #endif
   
   static pool_cache_t uvm_uarea_cache;
   
   static int
   uarea_ctor(void *arg, void *obj, int flags)
   {
   
           KASSERT((flags & PR_WAITOK) != 0);
           return uarea_swapin((vaddr_t)obj);
   }
   
   static void *
   uarea_poolpage_alloc(struct pool *pp, int flags)
   {
   
           return (void *)uvm_km_alloc(kernel_map, pp->pr_alloc->pa_pagesz,
               USPACE_ALIGN, UVM_KMF_PAGEABLE |
               ((flags & PR_WAITOK) != 0 ? UVM_KMF_WAITVA :
               (UVM_KMF_NOWAIT | UVM_KMF_TRYLOCK)));
   }
   
   static void
   uarea_poolpage_free(struct pool *pp, void *addr)
   {
   
           uvm_km_free(kernel_map, (vaddr_t)addr, pp->pr_alloc->pa_pagesz,
               UVM_KMF_PAGEABLE);
   }
   
   static struct pool_allocator uvm_uarea_allocator = {
           .pa_alloc = uarea_poolpage_alloc,
           .pa_free = uarea_poolpage_free,
           .pa_pagesz = USPACE,
   };
   
   void
   uvm_uarea_init(void)
   {
           int flags = PR_NOTOUCH;
   
           /*
            * specify PR_NOALIGN unless the alignment provided by
            * the backend (USPACE_ALIGN) is sufficient to provide
            * pool page size (UPSACE) alignment.
            */
   
           if ((USPACE_ALIGN == 0 && USPACE != PAGE_SIZE) ||
               (USPACE_ALIGN % USPACE) != 0) {
                   flags |= PR_NOALIGN;
           }
   
           uvm_uarea_cache = pool_cache_init(USPACE, USPACE_ALIGN, 0, flags,
               "uarea", &uvm_uarea_allocator, IPL_NONE, uarea_ctor, NULL, NULL);
   }
   
   /*
    * uvm_uarea_alloc: allocate a u-area
    */
   
   bool
   uvm_uarea_alloc(vaddr_t *uaddrp)
   {
   
           *uaddrp = (vaddr_t)pool_cache_get(uvm_uarea_cache, PR_WAITOK);
           return true;
   }
   
   /*
    * uvm_uarea_free: free a u-area
    */
   
   void
   uvm_uarea_free(vaddr_t uaddr, struct cpu_info *ci)
   {
   
           pool_cache_put(uvm_uarea_cache, (void *)uaddr);
   }
   
   /*
    * uvm_proc_exit: exit a virtual address space
    *
    * - borrow proc0's address space because freeing the vmspace
    *   of the dead process may block.
    */
   
   void
   uvm_proc_exit(struct proc *p)
   {
           struct lwp *l = curlwp; /* XXX */
           struct vmspace *ovm;
   
           KASSERT(p == l->l_proc);
           ovm = p->p_vmspace;
   
           /*
            * borrow proc0's address space.
            */
           KPREEMPT_DISABLE(l);
           pmap_deactivate(l);
           p->p_vmspace = proc0.p_vmspace;
           pmap_activate(l);
           KPREEMPT_ENABLE(l);
   
           uvmspace_free(ovm);
   }
   
   void
   uvm_lwp_exit(struct lwp *l)
   {
           vaddr_t va = USER_TO_UAREA(l->l_addr);
   
           l->l_flag &= ~LW_INMEM;
           uvm_uarea_free(va, l->l_cpu);
           l->l_addr = NULL;
   }
   
   /*
    * uvm_init_limit: init per-process VM limits
    *
    * - called for process 0 and then inherited by all others.
    */
   
   void
   uvm_init_limits(struct proc *p)
   {
   
           /*
            * Set up the initial limits on process VM.  Set the maximum
            * resident set size to be all of (reasonably) available memory.
            * This causes any single, large process to start random page
            * replacement once it fills memory.
            */
   
           p->p_rlimit[RLIMIT_STACK].rlim_cur = DFLSSIZ;
           p->p_rlimit[RLIMIT_STACK].rlim_max = maxsmap;
           p->p_rlimit[RLIMIT_DATA].rlim_cur = DFLDSIZ;
           p->p_rlimit[RLIMIT_DATA].rlim_max = maxdmap;
           p->p_rlimit[RLIMIT_AS].rlim_cur = RLIM_INFINITY;
           p->p_rlimit[RLIMIT_AS].rlim_max = RLIM_INFINITY;
           p->p_rlimit[RLIMIT_RSS].rlim_cur = ptoa(uvmexp.free);
   }
   
   #ifdef DEBUG
   int     enableswap = 1;
   int     swapdebug = 0;
   #define SDB_FOLLOW      1
   #define SDB_SWAPIN      2
   #define SDB_SWAPOUT     4
   #endif
   
   /*
    * uvm_swapin: swap in an lwp's u-area.
    *
    * - must be called with the LWP's swap lock held.
    * - naturally, must not be called with l == curlwp
    */
   
   void
   uvm_swapin(struct lwp *l)
   {
           int error;
   
           /* XXXSMP notyet KASSERT(mutex_owned(&l->l_swaplock)); */
           KASSERT(l != curlwp);
   
           error = uarea_swapin(USER_TO_UAREA(l->l_addr));
           if (error) {
                   panic("%s: rewiring stack failed: %d", __func__, error);
           }
   
           /*
            * Some architectures need to be notified when the user area has
            * moved to new physical page(s) (e.g.  see mips/mips/vm_machdep.c).
            */
           cpu_swapin(l);
           lwp_lock(l);
           if (l->l_stat == LSRUN)
                   sched_enqueue(l, false);
           l->l_flag |= LW_INMEM;
           l->l_swtime = 0;
           lwp_unlock(l);
           ++uvmexp.swapins;
   }
   
   /*
    * uvm_kick_scheduler: kick the scheduler into action if not running.
    *
    * - called when swapped out processes have been awoken.
    */
   
   void
   uvm_kick_scheduler(void)
   {
   
           if (uvm.swap_running == false)
                   return;
   
           mutex_enter(&uvm_scheduler_mutex);
           uvm.scheduler_kicked = true;
           cv_signal(&uvm.scheduler_cv);
           mutex_exit(&uvm_scheduler_mutex);
   }
   
   /*
    * uvm_scheduler: process zero main loop
    *
    * - attempt to swapin every swaped-out, runnable process in order of
    *      priority.
    * - if not enough memory, wake the pagedaemon and let it clear space.
    */
   
   void
   uvm_scheduler(void)
   {
           struct lwp *l, *ll;
           int pri;
           int ppri;
   
           l = curlwp;
           lwp_lock(l);
           l->l_priority = PRI_VM;
           l->l_class = SCHED_FIFO;
           lwp_unlock(l);
   
           for (;;) {
   #ifdef DEBUG
                   mutex_enter(&uvm_scheduler_mutex);
                   while (!enableswap)
                           cv_wait(&uvm.scheduler_cv, &uvm_scheduler_mutex);
                   mutex_exit(&uvm_scheduler_mutex);
   #endif
                   ll = NULL;              /* process to choose */
                   ppri = INT_MIN;         /* its priority */
   
                   mutex_enter(proc_lock);
                   LIST_FOREACH(l, &alllwp, l_list) {
                           /* is it a runnable swapped out process? */
                           if (l->l_stat == LSRUN && !(l->l_flag & LW_INMEM)) {
                                   pri = l->l_swtime + l->l_slptime -
                                       (l->l_proc->p_nice - NZERO) * 8;
                                   if (pri > ppri) {   /* higher priority? */
                                           ll = l;
                                           ppri = pri;
                                   }
                           }
                   }
   #ifdef DEBUG
                   if (swapdebug & SDB_FOLLOW)
                           printf("%s: running, procp %p pri %d\n", __func__, ll,
                               ppri);
   #endif
                   /*
                    * Nothing to do, back to sleep
                    */
                   if ((l = ll) == NULL) {
                           mutex_exit(proc_lock);
                           mutex_enter(&uvm_scheduler_mutex);
                           if (uvm.scheduler_kicked == false)
                                   cv_wait(&uvm.scheduler_cv,
                                       &uvm_scheduler_mutex);
                           uvm.scheduler_kicked = false;
                           mutex_exit(&uvm_scheduler_mutex);
                           continue;
                   }
   
                   /*
                    * we have found swapped out process which we would like
                    * to bring back in.
                    *
                    * XXX: this part is really bogus cuz we could deadlock
                    * on memory despite our feeble check
                    */
                   if (uvmexp.free > atop(USPACE)) {
   #ifdef DEBUG
                           if (swapdebug & SDB_SWAPIN)
                                   printf("swapin: pid %d(%s)@%p, pri %d "
                                       "free %d\n", l->l_proc->p_pid,
                                       l->l_proc->p_comm, l->l_addr, ppri,
                                       uvmexp.free);
   #endif
                           mutex_enter(&l->l_swaplock);
                           mutex_exit(proc_lock);
                           uvm_swapin(l);
                           mutex_exit(&l->l_swaplock);
                           continue;
                   } else {
                           /*
                            * not enough memory, jab the pageout daemon and
                            * wait til the coast is clear
                            */
                           mutex_exit(proc_lock);
   #ifdef DEBUG
                           if (swapdebug & SDB_FOLLOW)
                                   printf("%s: no room for pid %d(%s),"
                                       " free %d\n", __func__, l->l_proc->p_pid,
                                       l->l_proc->p_comm, uvmexp.free);
   #endif
                           uvm_wait("schedpwait");
   #ifdef DEBUG
                           if (swapdebug & SDB_FOLLOW)
                                   printf("%s: room again, free %d\n", __func__,
                                       uvmexp.free);
   #endif
                   }
           }
   }
   
   /*
    * swappable: is LWP "l" swappable?
    */
   
   static bool
   swappable(struct lwp *l)
   {
   
           if ((l->l_flag & (LW_INMEM|LW_SYSTEM|LW_WEXIT)) != LW_INMEM)
                   return false;
           if ((l->l_pflag & LP_RUNNING) != 0)
                   return false;
           if (l->l_holdcnt != 0)
                   return false;
           if (l->l_class != SCHED_OTHER)
                   return false;
           if (l->l_syncobj == &rw_syncobj || l->l_syncobj == &mutex_syncobj)
                   return false;
           if (l->l_proc->p_stat != SACTIVE && l->l_proc->p_stat != SSTOP)
                   return false;
           return true;
   }
   
   /*
    * swapout_threads: find threads that can be swapped and unwire their
    *      u-areas.
    *
    * - called by the pagedaemon
    * - try and swap at least one processs
    * - processes that are sleeping or stopped for maxslp or more seconds
    *   are swapped... otherwise the longest-sleeping or stopped process
    *   is swapped, otherwise the longest resident process...
    */
   
   void
   uvm_swapout_threads(void)
   {
           struct lwp *l;
           struct lwp *outl, *outl2;
           int outpri, outpri2;
           int didswap = 0;
           extern int maxslp;
           bool gotit;
   
           /* XXXCDC: should move off to uvmexp. or uvm., also in uvm_meter */
   
   #ifdef DEBUG
           if (!enableswap)
                   return;
   #endif
   
           /*
            * outl/outpri  : stop/sleep thread with largest sleeptime < maxslp
            * outl2/outpri2: the longest resident thread (its swap time)
            */
           outl = outl2 = NULL;
           outpri = outpri2 = 0;
   
    restart:
           mutex_enter(proc_lock);
           LIST_FOREACH(l, &alllwp, l_list) {
                   KASSERT(l->l_proc != NULL);
                   if (!mutex_tryenter(&l->l_swaplock))
                           continue;
                   if (!swappable(l)) {
                           mutex_exit(&l->l_swaplock);
                           continue;
                   }
                   switch (l->l_stat) {
                   case LSONPROC:
                           break;
   
                   case LSRUN:
                           if (l->l_swtime > outpri2) {
                                   outl2 = l;
                                   outpri2 = l->l_swtime;
                           }
                           break;
   
                   case LSSLEEP:
                   case LSSTOP:
                           if (l->l_slptime >= maxslp) {
                                   mutex_exit(proc_lock);
                                   uvm_swapout(l);
                                   /*
                                    * Locking in the wrong direction -
                                    * try to prevent the LWP from exiting.
                                    */
                                   gotit = mutex_tryenter(proc_lock);
                                   mutex_exit(&l->l_swaplock);
                                   didswap++;
                                   if (!gotit)
                                           goto restart;
                                   continue;
                           } else if (l->l_slptime > outpri) {
                                   outl = l;
                                   outpri = l->l_slptime;
                           }
                           break;
                   }
                   mutex_exit(&l->l_swaplock);
           }
   
           /*
            * If we didn't get rid of any real duds, toss out the next most
            * likely sleeping/stopped or running candidate.  We only do this
            * if we are real low on memory since we don't gain much by doing
            * it (USPACE bytes).
            */
           if (didswap == 0 && uvmexp.free <= atop(round_page(USPACE))) {
                   if ((l = outl) == NULL)
                           l = outl2;
   #ifdef DEBUG
                   if (swapdebug & SDB_SWAPOUT)
                           printf("%s: no duds, try procp %p\n", __func__, l);
   #endif
                   if (l) {
                           mutex_enter(&l->l_swaplock);
                           mutex_exit(proc_lock);
                           if (swappable(l))
                                   uvm_swapout(l);
                           mutex_exit(&l->l_swaplock);
                           return;
                   }
           }
   
           mutex_exit(proc_lock);
   }
   
   /*
    * uvm_swapout: swap out lwp "l"
    *
    * - currently "swapout" means "unwire U-area" and "pmap_collect()"
    *   the pmap.
    * - must be called with l->l_swaplock held.
    * - XXXCDC: should deactivate all process' private anonymous memory
    */
   
   static void
   uvm_swapout(struct lwp *l)
   {
           struct vm_map *map;
   
           KASSERT(mutex_owned(&l->l_swaplock));
   
   #ifdef DEBUG
           if (swapdebug & SDB_SWAPOUT)
                   printf("%s: lid %d.%d(%s)@%p, stat %x pri %d free %d\n",
                      __func__, l->l_proc->p_pid, l->l_lid, l->l_proc->p_comm,
                      l->l_addr, l->l_stat, l->l_slptime, uvmexp.free);
   #endif
   
           /*
            * Mark it as (potentially) swapped out.
            */
           lwp_lock(l);
           if (!swappable(l)) {
                   KDASSERT(l->l_cpu != curcpu());
                   lwp_unlock(l);
                   return;
           }
           l->l_flag &= ~LW_INMEM;
           l->l_swtime = 0;
           if (l->l_stat == LSRUN)
                   sched_dequeue(l);
           lwp_unlock(l);
           l->l_ru.ru_nswap++;
           ++uvmexp.swapouts;
   
           /*
            * Do any machine-specific actions necessary before swapout.
            * This can include saving floating point state, etc.
            */
           cpu_swapout(l);
   
           /*
            * Unwire the to-be-swapped process's user struct and kernel stack.
            */
           uarea_swapout(USER_TO_UAREA(l->l_addr));
           map = &l->l_proc->p_vmspace->vm_map;
           if (vm_map_lock_try(map)) {
                   pmap_collect(vm_map_pmap(map));
                   vm_map_unlock(map);
           }
   }
   
   /*
    * uvm_lwp_hold: prevent lwp "l" from being swapped out, and bring
    * back into memory if it is currently swapped.
    */
    
   void
   uvm_lwp_hold(struct lwp *l)
   {
   
           if (l == curlwp) {
                   atomic_inc_uint(&l->l_holdcnt);
           } else {
                   mutex_enter(&l->l_swaplock);
                   if (atomic_inc_uint_nv(&l->l_holdcnt) == 1 &&
                       (l->l_flag & LW_INMEM) == 0)
                           uvm_swapin(l);
                   mutex_exit(&l->l_swaplock);
           }
   }
   
   /*
    * uvm_lwp_rele: release a hold on lwp "l".  when the holdcount
    * drops to zero, it's eligable to be swapped.
    */
    
   void
   uvm_lwp_rele(struct lwp *l)
   {
   
           KASSERT(l->l_holdcnt != 0);
   
           atomic_dec_uint(&l->l_holdcnt);
   }
   
   #ifdef COREDUMP
   /*
    * uvm_coredump_walkmap: walk a process's map for the purpose of dumping
    * a core file.
    */
   
   int
   uvm_coredump_walkmap(struct proc *p, void *iocookie,
       int (*func)(struct proc *, void *, struct uvm_coredump_state *),
       void *cookie)
   {
           struct uvm_coredump_state state;
           struct vmspace *vm = p->p_vmspace;
           struct vm_map *map = &vm->vm_map;
           struct vm_map_entry *entry;
           int error;
   
           entry = NULL;
           vm_map_lock_read(map);
           state.end = 0;
           for (;;) {
                   if (entry == NULL)
                           entry = map->header.next;
                   else if (!uvm_map_lookup_entry(map, state.end, &entry))
                           entry = entry->next;
                   if (entry == &map->header)
                           break;
   
                   state.cookie = cookie;
                   if (state.end > entry->start) {
                           state.start = state.end;
                   } else {
                           state.start = entry->start;
                   }
                   state.realend = entry->end;
                   state.end = entry->end;
                   state.prot = entry->protection;
                   state.flags = 0;
   
                   /*
                    * Dump the region unless one of the following is true:
                    *
                    * (1) the region has neither object nor amap behind it
                    *     (ie. it has never been accessed).
                    *
                    * (2) the region has no amap and is read-only
                    *     (eg. an executable text section).
                    *
                    * (3) the region's object is a device.
                    *
                    * (4) the region is unreadable by the process.
                    */
   
                   KASSERT(!UVM_ET_ISSUBMAP(entry));
                   KASSERT(state.start < VM_MAXUSER_ADDRESS);
                   KASSERT(state.end <= VM_MAXUSER_ADDRESS);
                   if (entry->object.uvm_obj == NULL &&
                       entry->aref.ar_amap == NULL) {
                           state.realend = state.start;
                   } else if ((entry->protection & VM_PROT_WRITE) == 0 &&
                       entry->aref.ar_amap == NULL) {
                           state.realend = state.start;
                   } else if (entry->object.uvm_obj != NULL &&
                       UVM_OBJ_IS_DEVICE(entry->object.uvm_obj)) {
                           state.realend = state.start;
                   } else if ((entry->protection & VM_PROT_READ) == 0) {
                           state.realend = state.start;
                   } else {
                           if (state.start >= (vaddr_t)vm->vm_maxsaddr)
                                   state.flags |= UVM_COREDUMP_STACK;
   
                           /*
                            * If this an anonymous entry, only dump instantiated
                            * pages.
                            */
                           if (entry->object.uvm_obj == NULL) {
                                   vaddr_t end;
   
                                   amap_lock(entry->aref.ar_amap);
                                   for (end = state.start;
                                        end < state.end; end += PAGE_SIZE) {
                                           struct vm_anon *anon;
                                           anon = amap_lookup(&entry->aref,
                                               end - entry->start);
                                           /*
                                            * If we have already encountered an
                                            * uninstantiated page, stop at the
                                            * first instantied page.
                                            */
                                           if (anon != NULL &&
                                               state.realend != state.end) {
                                                   state.end = end;
                                                   break;
                                           }
   
                                           /*
                                            * If this page is the first
                                            * uninstantiated page, mark this as
                                            * the real ending point.  Continue to
                                            * counting uninstantiated pages.
                                            */
                                           if (anon == NULL &&
                                               state.realend == state.end) {
                                                   state.realend = end;
                                           }
                                   }
                                   amap_unlock(entry->aref.ar_amap);
                           }
                   }
                   
   
                   vm_map_unlock_read(map);
                   error = (*func)(p, iocookie, &state);
                   if (error)
                           return (error);
                   vm_map_lock_read(map);
           }
           vm_map_unlock_read(map);
   
           return (0);
   }
   #endif /* COREDUMP */

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