text: /*-
   * Copyright (c) 1998 Matthew Dillon,
   * Copyright (c) 1994 John S. Dyson
   * Copyright (c) 1990 University of Utah.
   * Copyright (c) 1982, 1986, 1989, 1993
   *	The Regents of the University of California.  All rights reserved.
   *
   * This code is derived from software contributed to Berkeley by
   * the Systems Programming Group of the University of Utah Computer
   * Science Department.
   *
   * 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 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.
   *
   *				New Swap System
   *				Matthew Dillon
   *
   * Radix Bitmap 'blists'.
   *
   *	- The new swapper uses the new radix bitmap code.  This should scale
   *	  to arbitrarily small or arbitrarily large swap spaces and an almost
   *	  arbitrary degree of fragmentation.
   *
   * Features:
   *
   *	- on the fly reallocation of swap during putpages.  The new system
   *	  does not try to keep previously allocated swap blocks for dirty
   *	  pages.  
   *
   *	- on the fly deallocation of swap
   *
   *	- No more garbage collection required.  Unnecessarily allocated swap
   *	  blocks only exist for dirty vm_page_t's now and these are already
   *	  cycled (in a high-load system) by the pager.  We also do on-the-fly
   *	  removal of invalidated swap blocks when a page is destroyed
   *	  or renamed.
   *
   * from: Utah $Hdr: swap_pager.c 1.4 91/04/30$
   *
   *	@(#)swap_pager.c	8.9 (Berkeley) 3/21/94
   *	@(#)vm_swap.c	8.5 (Berkeley) 2/17/94
   */
  
  #include <sys/cdefs.h>
  __FBSDID("$FreeBSD: releng/9.3/sys/vm/swap_pager.c 253257 2013-07-12 10:02:47Z kib $");
  
  #include "opt_swap.h"
  #include "opt_vm.h"
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/conf.h>
  #include <sys/kernel.h>
  #include <sys/priv.h>
  #include <sys/proc.h>
  #include <sys/bio.h>
  #include <sys/buf.h>
  #include <sys/disk.h>
  #include <sys/fcntl.h>
  #include <sys/mount.h>
  #include <sys/namei.h>
  #include <sys/vnode.h>
  #include <sys/malloc.h>
  #include <sys/racct.h>
  #include <sys/resource.h>
  #include <sys/resourcevar.h>
  #include <sys/sysctl.h>
  #include <sys/sysproto.h>
  #include <sys/blist.h>
  #include <sys/lock.h>
  #include <sys/sx.h>
  #include <sys/vmmeter.h>
  
  #include <security/mac/mac_framework.h>
  
  #include <vm/vm.h>
  #include <vm/pmap.h>
  #include <vm/vm_map.h>
  #include <vm/vm_kern.h>
  #include <vm/vm_object.h>
  #include <vm/vm_page.h>
  #include <vm/vm_pager.h>
  #include <vm/vm_pageout.h>
  #include <vm/vm_param.h>
  #include <vm/swap_pager.h>
  #include <vm/vm_extern.h>
  #include <vm/uma.h>
  
  #include <geom/geom.h>
  
  /*
   * SWB_NPAGES must be a power of 2.  It may be set to 1, 2, 4, 8, 16
   * or 32 pages per allocation.
   * The 32-page limit is due to the radix code (kern/subr_blist.c).
   */
  #ifndef MAX_PAGEOUT_CLUSTER
  #define MAX_PAGEOUT_CLUSTER 16
  #endif
  
  #if !defined(SWB_NPAGES)
  #define SWB_NPAGES	MAX_PAGEOUT_CLUSTER
  #endif
  
  /*
   * The swblock structure maps an object and a small, fixed-size range
   * of page indices to disk addresses within a swap area.
   * The collection of these mappings is implemented as a hash table.
   * Unused disk addresses within a swap area are allocated and managed
   * using a blist.
   */
  #define SWCORRECT(n) (sizeof(void *) * (n) / sizeof(daddr_t))
  #define SWAP_META_PAGES		(SWB_NPAGES * 2)
  #define SWAP_META_MASK		(SWAP_META_PAGES - 1)
  
  struct swblock {
  	struct swblock	*swb_hnext;
  	vm_object_t	swb_object;
  	vm_pindex_t	swb_index;
  	int		swb_count;
  	daddr_t		swb_pages[SWAP_META_PAGES];
  };
  
  static MALLOC_DEFINE(M_VMPGDATA, "vm_pgdata", "swap pager private data");
  static struct mtx sw_dev_mtx;
  static TAILQ_HEAD(, swdevt) swtailq = TAILQ_HEAD_INITIALIZER(swtailq);
  static struct swdevt *swdevhd;	/* Allocate from here next */
  static int nswapdev;		/* Number of swap devices */
  int swap_pager_avail;
  static int swdev_syscall_active = 0; /* serialize swap(on|off) */
  
  static vm_ooffset_t swap_total;
  SYSCTL_QUAD(_vm, OID_AUTO, swap_total, CTLFLAG_RD, &swap_total, 0, 
      "Total amount of available swap storage.");
  static vm_ooffset_t swap_reserved;
  SYSCTL_QUAD(_vm, OID_AUTO, swap_reserved, CTLFLAG_RD, &swap_reserved, 0, 
      "Amount of swap storage needed to back all allocated anonymous memory.");
  static int overcommit = 0;
  SYSCTL_INT(_vm, OID_AUTO, overcommit, CTLFLAG_RW, &overcommit, 0, 
      "Configure virtual memory overcommit behavior. See tuning(7) "
      "for details.");
  
  /* bits from overcommit */
  #define	SWAP_RESERVE_FORCE_ON		(1 << 0)
  #define	SWAP_RESERVE_RLIMIT_ON		(1 << 1)
  #define	SWAP_RESERVE_ALLOW_NONWIRED	(1 << 2)
  
  int
  swap_reserve(vm_ooffset_t incr)
  {
  
  	return (swap_reserve_by_cred(incr, curthread->td_ucred));
  }
  
  int
  swap_reserve_by_cred(vm_ooffset_t incr, struct ucred *cred)
  {
  	vm_ooffset_t r, s;
  	int res, error;
  	static int curfail;
  	static struct timeval lastfail;
  	struct uidinfo *uip;
  	
  	uip = cred->cr_ruidinfo;
  
  	if (incr & PAGE_MASK)
  		panic("swap_reserve: & PAGE_MASK");
  
  #ifdef RACCT
  	PROC_LOCK(curproc);
  	error = racct_add(curproc, RACCT_SWAP, incr);
  	PROC_UNLOCK(curproc);
  	if (error != 0)
  		return (0);
  #endif
  
  	res = 0;
  	mtx_lock(&sw_dev_mtx);
  	r = swap_reserved + incr;
  	if (overcommit & SWAP_RESERVE_ALLOW_NONWIRED) {
  		s = cnt.v_page_count - cnt.v_free_reserved - cnt.v_wire_count;
  		s *= PAGE_SIZE;
  	} else
  		s = 0;
  	s += swap_total;
  	if ((overcommit & SWAP_RESERVE_FORCE_ON) == 0 || r <= s ||
  	    (error = priv_check(curthread, PRIV_VM_SWAP_NOQUOTA)) == 0) {
  		res = 1;
  		swap_reserved = r;
  	}
  	mtx_unlock(&sw_dev_mtx);
  
  	if (res) {
  		PROC_LOCK(curproc);
  		UIDINFO_VMSIZE_LOCK(uip);
  		if ((overcommit & SWAP_RESERVE_RLIMIT_ON) != 0 &&
  		    uip->ui_vmsize + incr > lim_cur(curproc, RLIMIT_SWAP) &&
  		    priv_check(curthread, PRIV_VM_SWAP_NORLIMIT))
  			res = 0;
  		else
  			uip->ui_vmsize += incr;
  		UIDINFO_VMSIZE_UNLOCK(uip);
  		PROC_UNLOCK(curproc);
  		if (!res) {
  			mtx_lock(&sw_dev_mtx);
  			swap_reserved -= incr;
  			mtx_unlock(&sw_dev_mtx);
  		}
  	}
  	if (!res && ppsratecheck(&lastfail, &curfail, 1)) {
  		printf("uid %d, pid %d: swap reservation for %jd bytes failed\n",
  		    uip->ui_uid, curproc->p_pid, incr);
  	}
  
  #ifdef RACCT
  	if (!res) {
  		PROC_LOCK(curproc);
  		racct_sub(curproc, RACCT_SWAP, incr);
  		PROC_UNLOCK(curproc);
  	}
  #endif
  
  	return (res);
  }
  
  void
  swap_reserve_force(vm_ooffset_t incr)
  {
  	struct uidinfo *uip;
  
  	mtx_lock(&sw_dev_mtx);
  	swap_reserved += incr;
  	mtx_unlock(&sw_dev_mtx);
  
  #ifdef RACCT
  	PROC_LOCK(curproc);
  	racct_add_force(curproc, RACCT_SWAP, incr);
  	PROC_UNLOCK(curproc);
  #endif
  
  	uip = curthread->td_ucred->cr_ruidinfo;
  	PROC_LOCK(curproc);
  	UIDINFO_VMSIZE_LOCK(uip);
  	uip->ui_vmsize += incr;
  	UIDINFO_VMSIZE_UNLOCK(uip);
  	PROC_UNLOCK(curproc);
  }
  
  void
  swap_release(vm_ooffset_t decr)
  {
  	struct ucred *cred;
  
  	PROC_LOCK(curproc);
  	cred = curthread->td_ucred;
  	swap_release_by_cred(decr, cred);
  	PROC_UNLOCK(curproc);
  }
  
  void
  swap_release_by_cred(vm_ooffset_t decr, struct ucred *cred)
  {
   	struct uidinfo *uip;
  	
  	uip = cred->cr_ruidinfo;
  
  	if (decr & PAGE_MASK)
  		panic("swap_release: & PAGE_MASK");
  
  	mtx_lock(&sw_dev_mtx);
  	if (swap_reserved < decr)
  		panic("swap_reserved < decr");
  	swap_reserved -= decr;
  	mtx_unlock(&sw_dev_mtx);
  
  	UIDINFO_VMSIZE_LOCK(uip);
  	if (uip->ui_vmsize < decr)
  		printf("negative vmsize for uid = %d\n", uip->ui_uid);
  	uip->ui_vmsize -= decr;
  	UIDINFO_VMSIZE_UNLOCK(uip);
  
  	racct_sub_cred(cred, RACCT_SWAP, decr);
  }
  
  static void swapdev_strategy(struct buf *, struct swdevt *sw);
  
  #define SWM_FREE	0x02	/* free, period			*/
  #define SWM_POP		0x04	/* pop out			*/
  
  int swap_pager_full = 2;	/* swap space exhaustion (task killing) */
  static int swap_pager_almost_full = 1; /* swap space exhaustion (w/hysteresis)*/
  static int nsw_rcount;		/* free read buffers			*/
  static int nsw_wcount_sync;	/* limit write buffers / synchronous	*/
  static int nsw_wcount_async;	/* limit write buffers / asynchronous	*/
  static int nsw_wcount_async_max;/* assigned maximum			*/
  static int nsw_cluster_max;	/* maximum VOP I/O allowed		*/
  
  static struct swblock **swhash;
  static int swhash_mask;
  static struct mtx swhash_mtx;
  
  static int swap_async_max = 4;	/* maximum in-progress async I/O's	*/
  static struct sx sw_alloc_sx;
  
  
  SYSCTL_INT(_vm, OID_AUTO, swap_async_max,
          CTLFLAG_RW, &swap_async_max, 0, "Maximum running async swap ops");
  
  /*
   * "named" and "unnamed" anon region objects.  Try to reduce the overhead
   * of searching a named list by hashing it just a little.
   */
  
  #define NOBJLISTS		8
  
  #define NOBJLIST(handle)	\
  	(&swap_pager_object_list[((int)(intptr_t)handle >> 4) & (NOBJLISTS-1)])
  
  static struct mtx sw_alloc_mtx;	/* protect list manipulation */ 
  static struct pagerlst	swap_pager_object_list[NOBJLISTS];
  static uma_zone_t	swap_zone;
  static struct vm_object	swap_zone_obj;
  
  /*
   * pagerops for OBJT_SWAP - "swap pager".  Some ops are also global procedure
   * calls hooked from other parts of the VM system and do not appear here.
   * (see vm/swap_pager.h).
   */
  static vm_object_t
  		swap_pager_alloc(void *handle, vm_ooffset_t size,
  		    vm_prot_t prot, vm_ooffset_t offset, struct ucred *);
  static void	swap_pager_dealloc(vm_object_t object);
  static int	swap_pager_getpages(vm_object_t, vm_page_t *, int, int);
  static void	swap_pager_putpages(vm_object_t, vm_page_t *, int, boolean_t, int *);
  static boolean_t
  		swap_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before, int *after);
  static void	swap_pager_init(void);
  static void	swap_pager_unswapped(vm_page_t);
  static void	swap_pager_swapoff(struct swdevt *sp);
  
  struct pagerops swappagerops = {
  	.pgo_init =	swap_pager_init,	/* early system initialization of pager	*/
  	.pgo_alloc =	swap_pager_alloc,	/* allocate an OBJT_SWAP object		*/
  	.pgo_dealloc =	swap_pager_dealloc,	/* deallocate an OBJT_SWAP object	*/
  	.pgo_getpages =	swap_pager_getpages,	/* pagein				*/
  	.pgo_putpages =	swap_pager_putpages,	/* pageout				*/
  	.pgo_haspage =	swap_pager_haspage,	/* get backing store status for page	*/
  	.pgo_pageunswapped = swap_pager_unswapped,	/* remove swap related to page		*/
  };
  
  /*
   * dmmax is in page-sized chunks with the new swap system.  It was
   * dev-bsized chunks in the old.  dmmax is always a power of 2.
   *
   * swap_*() routines are externally accessible.  swp_*() routines are
   * internal.
   */
  static int dmmax;
  static int nswap_lowat = 128;	/* in pages, swap_pager_almost_full warn */
  static int nswap_hiwat = 512;	/* in pages, swap_pager_almost_full warn */
  
  SYSCTL_INT(_vm, OID_AUTO, dmmax,
  	CTLFLAG_RD, &dmmax, 0, "Maximum size of a swap block");
  
  static void	swp_sizecheck(void);
  static void	swp_pager_async_iodone(struct buf *bp);
  static int	swapongeom(struct thread *, struct vnode *);
  static int	swaponvp(struct thread *, struct vnode *, u_long);
  static int	swapoff_one(struct swdevt *sp, struct ucred *cred);
  
  /*
   * Swap bitmap functions
   */
  static void	swp_pager_freeswapspace(daddr_t blk, int npages);
  static daddr_t	swp_pager_getswapspace(int npages);
  
  /*
   * Metadata functions
   */
  static struct swblock **swp_pager_hash(vm_object_t object, vm_pindex_t index);
  static void swp_pager_meta_build(vm_object_t, vm_pindex_t, daddr_t);
  static void swp_pager_meta_free(vm_object_t, vm_pindex_t, daddr_t);
  static void swp_pager_meta_free_all(vm_object_t);
  static daddr_t swp_pager_meta_ctl(vm_object_t, vm_pindex_t, int);
  
  static void
  swp_pager_free_nrpage(vm_page_t m)
  {
  
  	vm_page_lock(m);
  	if (m->wire_count == 0)
  		vm_page_free(m);
  	vm_page_unlock(m);
  }
  
  /*
   * SWP_SIZECHECK() -	update swap_pager_full indication
   *	
   *	update the swap_pager_almost_full indication and warn when we are
   *	about to run out of swap space, using lowat/hiwat hysteresis.
   *
   *	Clear swap_pager_full ( task killing ) indication when lowat is met.
   *
   *	No restrictions on call
   *	This routine may not block.
   */
  static void
  swp_sizecheck(void)
  {
  
  	if (swap_pager_avail < nswap_lowat) {
  		if (swap_pager_almost_full == 0) {
  			printf("swap_pager: out of swap space\n");
  			swap_pager_almost_full = 1;
  		}
  	} else {
  		swap_pager_full = 0;
  		if (swap_pager_avail > nswap_hiwat)
  			swap_pager_almost_full = 0;
  	}
  }
  
  /*
   * SWP_PAGER_HASH() -	hash swap meta data
   *
   *	This is an helper function which hashes the swapblk given
   *	the object and page index.  It returns a pointer to a pointer
   *	to the object, or a pointer to a NULL pointer if it could not
   *	find a swapblk.
   */
  static struct swblock **
  swp_pager_hash(vm_object_t object, vm_pindex_t index)
  {
  	struct swblock **pswap;
  	struct swblock *swap;
  
  	index &= ~(vm_pindex_t)SWAP_META_MASK;
  	pswap = &swhash[(index ^ (int)(intptr_t)object) & swhash_mask];
  	while ((swap = *pswap) != NULL) {
  		if (swap->swb_object == object &&
  		    swap->swb_index == index
  		) {
  			break;
  		}
  		pswap = &swap->swb_hnext;
  	}
  	return (pswap);
  }
  
  /*
   * SWAP_PAGER_INIT() -	initialize the swap pager!
   *
   *	Expected to be started from system init.  NOTE:  This code is run 
   *	before much else so be careful what you depend on.  Most of the VM
   *	system has yet to be initialized at this point.
   */
  static void
  swap_pager_init(void)
  {
  	/*
  	 * Initialize object lists
  	 */
  	int i;
  
  	for (i = 0; i < NOBJLISTS; ++i)
  		TAILQ_INIT(&swap_pager_object_list[i]);
  	mtx_init(&sw_alloc_mtx, "swap_pager list", NULL, MTX_DEF);
  	mtx_init(&sw_dev_mtx, "swapdev", NULL, MTX_DEF);
  
  	/*
  	 * Device Stripe, in PAGE_SIZE'd blocks
  	 */
  	dmmax = SWB_NPAGES * 2;
  }
  
  /*
   * SWAP_PAGER_SWAP_INIT() - swap pager initialization from pageout process
   *
   *	Expected to be started from pageout process once, prior to entering
   *	its main loop.
   */
  void
  swap_pager_swap_init(void)
  {
  	int n, n2;
  
  	/*
  	 * Number of in-transit swap bp operations.  Don't
  	 * exhaust the pbufs completely.  Make sure we
  	 * initialize workable values (0 will work for hysteresis
  	 * but it isn't very efficient).
  	 *
  	 * The nsw_cluster_max is constrained by the bp->b_pages[]
  	 * array (MAXPHYS/PAGE_SIZE) and our locally defined
  	 * MAX_PAGEOUT_CLUSTER.   Also be aware that swap ops are
  	 * constrained by the swap device interleave stripe size.
  	 *
  	 * Currently we hardwire nsw_wcount_async to 4.  This limit is 
  	 * designed to prevent other I/O from having high latencies due to
  	 * our pageout I/O.  The value 4 works well for one or two active swap
  	 * devices but is probably a little low if you have more.  Even so,
  	 * a higher value would probably generate only a limited improvement
  	 * with three or four active swap devices since the system does not
  	 * typically have to pageout at extreme bandwidths.   We will want
  	 * at least 2 per swap devices, and 4 is a pretty good value if you
  	 * have one NFS swap device due to the command/ack latency over NFS.
  	 * So it all works out pretty well.
  	 */
  	nsw_cluster_max = min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER);
  
  	mtx_lock(&pbuf_mtx);
  	nsw_rcount = (nswbuf + 1) / 2;
  	nsw_wcount_sync = (nswbuf + 3) / 4;
  	nsw_wcount_async = 4;
  	nsw_wcount_async_max = nsw_wcount_async;
  	mtx_unlock(&pbuf_mtx);
  
  	/*
  	 * Initialize our zone.  Right now I'm just guessing on the number
  	 * we need based on the number of pages in the system.  Each swblock
  	 * can hold 16 pages, so this is probably overkill.  This reservation
  	 * is typically limited to around 32MB by default.
  	 */
  	n = cnt.v_page_count / 2;
  	if (maxswzone && n > maxswzone / sizeof(struct swblock))
  		n = maxswzone / sizeof(struct swblock);
  	n2 = n;
  	swap_zone = uma_zcreate("SWAPMETA", sizeof(struct swblock), NULL, NULL,
  	    NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE | UMA_ZONE_VM);
  	if (swap_zone == NULL)
  		panic("failed to create swap_zone.");
  	do {
  		if (uma_zone_set_obj(swap_zone, &swap_zone_obj, n))
  			break;
  		/*
  		 * if the allocation failed, try a zone two thirds the
  		 * size of the previous attempt.
  		 */
  		n -= ((n + 2) / 3);
  	} while (n > 0);
  	if (n2 != n)
  		printf("Swap zone entries reduced from %d to %d.\n", n2, n);
  	n2 = n;
  
  	/*
  	 * Initialize our meta-data hash table.  The swapper does not need to
  	 * be quite as efficient as the VM system, so we do not use an 
  	 * oversized hash table.
  	 *
  	 * 	n: 		size of hash table, must be power of 2
  	 *	swhash_mask:	hash table index mask
  	 */
  	for (n = 1; n < n2 / 8; n *= 2)
  		;
  	swhash = malloc(sizeof(struct swblock *) * n, M_VMPGDATA, M_WAITOK | M_ZERO);
  	swhash_mask = n - 1;
  	mtx_init(&swhash_mtx, "swap_pager swhash", NULL, MTX_DEF);
  }
  
  /*
   * SWAP_PAGER_ALLOC() -	allocate a new OBJT_SWAP VM object and instantiate
   *			its metadata structures.
   *
   *	This routine is called from the mmap and fork code to create a new
   *	OBJT_SWAP object.  We do this by creating an OBJT_DEFAULT object
   *	and then converting it with swp_pager_meta_build().
   *
   *	This routine may block in vm_object_allocate() and create a named
   *	object lookup race, so we must interlock.
   *
   * MPSAFE
   */
  static vm_object_t
  swap_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
      vm_ooffset_t offset, struct ucred *cred)
  {
  	vm_object_t object;
  	vm_pindex_t pindex;
  
  	pindex = OFF_TO_IDX(offset + PAGE_MASK + size);
  	if (handle) {
  		mtx_lock(&Giant);
  		/*
  		 * Reference existing named region or allocate new one.  There
  		 * should not be a race here against swp_pager_meta_build()
  		 * as called from vm_page_remove() in regards to the lookup
  		 * of the handle.
  		 */
  		sx_xlock(&sw_alloc_sx);
  		object = vm_pager_object_lookup(NOBJLIST(handle), handle);
  		if (object == NULL) {
  			if (cred != NULL) {
  				if (!swap_reserve_by_cred(size, cred)) {
  					sx_xunlock(&sw_alloc_sx);
  					mtx_unlock(&Giant);
  					return (NULL);
  				}
  				crhold(cred);
  			}
  			object = vm_object_allocate(OBJT_DEFAULT, pindex);
  			VM_OBJECT_LOCK(object);
  			object->handle = handle;
  			if (cred != NULL) {
  				object->cred = cred;
  				object->charge = size;
  			}
  			swp_pager_meta_build(object, 0, SWAPBLK_NONE);
  			VM_OBJECT_UNLOCK(object);
  		}
  		sx_xunlock(&sw_alloc_sx);
  		mtx_unlock(&Giant);
  	} else {
  		if (cred != NULL) {
  			if (!swap_reserve_by_cred(size, cred))
  				return (NULL);
  			crhold(cred);
  		}
  		object = vm_object_allocate(OBJT_DEFAULT, pindex);
  		VM_OBJECT_LOCK(object);
  		if (cred != NULL) {
  			object->cred = cred;
  			object->charge = size;
  		}
  		swp_pager_meta_build(object, 0, SWAPBLK_NONE);
  		VM_OBJECT_UNLOCK(object);
  	}
  	return (object);
  }
  
  /*
   * SWAP_PAGER_DEALLOC() -	remove swap metadata from object
   *
   *	The swap backing for the object is destroyed.  The code is 
   *	designed such that we can reinstantiate it later, but this
   *	routine is typically called only when the entire object is
   *	about to be destroyed.
   *
   *	The object must be locked.
   */
  static void
  swap_pager_dealloc(vm_object_t object)
  {
  
  	/*
  	 * Remove from list right away so lookups will fail if we block for
  	 * pageout completion.
  	 */
  	if (object->handle != NULL) {
  		mtx_lock(&sw_alloc_mtx);
  		TAILQ_REMOVE(NOBJLIST(object->handle), object, pager_object_list);
  		mtx_unlock(&sw_alloc_mtx);
  	}
  
  	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  	vm_object_pip_wait(object, "swpdea");
  
  	/*
  	 * Free all remaining metadata.  We only bother to free it from 
  	 * the swap meta data.  We do not attempt to free swapblk's still
  	 * associated with vm_page_t's for this object.  We do not care
  	 * if paging is still in progress on some objects.
  	 */
  	swp_pager_meta_free_all(object);
  }
  
  /************************************************************************
   *			SWAP PAGER BITMAP ROUTINES			*
   ************************************************************************/
  
  /*
   * SWP_PAGER_GETSWAPSPACE() -	allocate raw swap space
   *
   *	Allocate swap for the requested number of pages.  The starting
   *	swap block number (a page index) is returned or SWAPBLK_NONE
   *	if the allocation failed.
   *
   *	Also has the side effect of advising that somebody made a mistake
   *	when they configured swap and didn't configure enough.
   *
   *	This routine may not sleep.
   *
   *	We allocate in round-robin fashion from the configured devices.
   */
  static daddr_t
  swp_pager_getswapspace(int npages)
  {
  	daddr_t blk;
  	struct swdevt *sp;
  	int i;
  
  	blk = SWAPBLK_NONE;
  	mtx_lock(&sw_dev_mtx);
  	sp = swdevhd;
  	for (i = 0; i < nswapdev; i++) {
  		if (sp == NULL)
  			sp = TAILQ_FIRST(&swtailq);
  		if (!(sp->sw_flags & SW_CLOSING)) {
  			blk = blist_alloc(sp->sw_blist, npages);
  			if (blk != SWAPBLK_NONE) {
  				blk += sp->sw_first;
  				sp->sw_used += npages;
  				swap_pager_avail -= npages;
  				swp_sizecheck();
  				swdevhd = TAILQ_NEXT(sp, sw_list);
  				goto done;
  			}
  		}
  		sp = TAILQ_NEXT(sp, sw_list);
  	}
  	if (swap_pager_full != 2) {
  		printf("swap_pager_getswapspace(%d): failed\n", npages);
  		swap_pager_full = 2;
  		swap_pager_almost_full = 1;
  	}
  	swdevhd = NULL;
  done:
  	mtx_unlock(&sw_dev_mtx);
  	return (blk);
  }
  
  static int
  swp_pager_isondev(daddr_t blk, struct swdevt *sp)
  {
  
  	return (blk >= sp->sw_first && blk < sp->sw_end);
  }
  	
  static void
  swp_pager_strategy(struct buf *bp)
  {
  	struct swdevt *sp;
  
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(sp, &swtailq, sw_list) {
  		if (bp->b_blkno >= sp->sw_first && bp->b_blkno < sp->sw_end) {
  			mtx_unlock(&sw_dev_mtx);
  			if ((sp->sw_flags & SW_UNMAPPED) != 0 &&
  			    unmapped_buf_allowed) {
  				bp->b_kvaalloc = bp->b_data;
  				bp->b_data = unmapped_buf;
  				bp->b_kvabase = unmapped_buf;
  				bp->b_offset = 0;
  				bp->b_flags |= B_UNMAPPED;
  			} else {
  				pmap_qenter((vm_offset_t)bp->b_data,
  				    &bp->b_pages[0], bp->b_bcount / PAGE_SIZE);
  			}
  			sp->sw_strategy(bp, sp);
  			return;
  		}
  	}
  	panic("Swapdev not found");
  }
  	
  
  /*
   * SWP_PAGER_FREESWAPSPACE() -	free raw swap space 
   *
   *	This routine returns the specified swap blocks back to the bitmap.
   *
   *	This routine may not sleep.
   */
  static void
  swp_pager_freeswapspace(daddr_t blk, int npages)
  {
  	struct swdevt *sp;
  
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(sp, &swtailq, sw_list) {
  		if (blk >= sp->sw_first && blk < sp->sw_end) {
  			sp->sw_used -= npages;
  			/*
  			 * If we are attempting to stop swapping on
  			 * this device, we don't want to mark any
  			 * blocks free lest they be reused.  
  			 */
  			if ((sp->sw_flags & SW_CLOSING) == 0) {
  				blist_free(sp->sw_blist, blk - sp->sw_first,
  				    npages);
  				swap_pager_avail += npages;
  				swp_sizecheck();
  			}
  			mtx_unlock(&sw_dev_mtx);
  			return;
  		}
  	}
  	panic("Swapdev not found");
  }
  
  /*
   * SWAP_PAGER_FREESPACE() -	frees swap blocks associated with a page
   *				range within an object.
   *
   *	This is a globally accessible routine.
   *
   *	This routine removes swapblk assignments from swap metadata.
   *
   *	The external callers of this routine typically have already destroyed 
   *	or renamed vm_page_t's associated with this range in the object so 
   *	we should be ok.
   */
  void
  swap_pager_freespace(vm_object_t object, vm_pindex_t start, vm_size_t size)
  {
  
  	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  	swp_pager_meta_free(object, start, size);
  }
  
  /*
   * SWAP_PAGER_RESERVE() - reserve swap blocks in object
   *
   *	Assigns swap blocks to the specified range within the object.  The 
   *	swap blocks are not zeroed.  Any previous swap assignment is destroyed.
   *
   *	Returns 0 on success, -1 on failure.
   */
  int
  swap_pager_reserve(vm_object_t object, vm_pindex_t start, vm_size_t size)
  {
  	int n = 0;
  	daddr_t blk = SWAPBLK_NONE;
  	vm_pindex_t beg = start;	/* save start index */
  
  	VM_OBJECT_LOCK(object);
  	while (size) {
  		if (n == 0) {
  			n = BLIST_MAX_ALLOC;
  			while ((blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE) {
  				n >>= 1;
  				if (n == 0) {
  					swp_pager_meta_free(object, beg, start - beg);
  					VM_OBJECT_UNLOCK(object);
  					return (-1);
  				}
  			}
  		}
  		swp_pager_meta_build(object, start, blk);
  		--size;
  		++start;
  		++blk;
  		--n;
  	}
  	swp_pager_meta_free(object, start, n);
  	VM_OBJECT_UNLOCK(object);
  	return (0);
  }
  
  /*
   * SWAP_PAGER_COPY() -  copy blocks from source pager to destination pager
   *			and destroy the source.
   *
   *	Copy any valid swapblks from the source to the destination.  In
   *	cases where both the source and destination have a valid swapblk,
   *	we keep the destination's.
   *
   *	This routine is allowed to sleep.  It may sleep allocating metadata
   *	indirectly through swp_pager_meta_build() or if paging is still in
   *	progress on the source. 
   *
   *	The source object contains no vm_page_t's (which is just as well)
   *
   *	The source object is of type OBJT_SWAP.
   *
   *	The source and destination objects must be locked.
   *	Both object locks may temporarily be released.
   */
  void
  swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
      vm_pindex_t offset, int destroysource)
  {
  	vm_pindex_t i;
  
  	VM_OBJECT_LOCK_ASSERT(srcobject, MA_OWNED);
  	VM_OBJECT_LOCK_ASSERT(dstobject, MA_OWNED);
  
  	/*
  	 * If destroysource is set, we remove the source object from the 
  	 * swap_pager internal queue now. 
  	 */
  	if (destroysource) {
  		if (srcobject->handle != NULL) {
  			mtx_lock(&sw_alloc_mtx);
  			TAILQ_REMOVE(
  			    NOBJLIST(srcobject->handle),
  			    srcobject,
  			    pager_object_list
  			);
  			mtx_unlock(&sw_alloc_mtx);
  		}
  	}
  
  	/*
  	 * transfer source to destination.
  	 */
  	for (i = 0; i < dstobject->size; ++i) {
  		daddr_t dstaddr;
  
  		/*
  		 * Locate (without changing) the swapblk on the destination,
  		 * unless it is invalid in which case free it silently, or
  		 * if the destination is a resident page, in which case the
  		 * source is thrown away.
  		 */
  		dstaddr = swp_pager_meta_ctl(dstobject, i, 0);
  
  		if (dstaddr == SWAPBLK_NONE) {
  			/*
  			 * Destination has no swapblk and is not resident,
  			 * copy source.
  			 */
  			daddr_t srcaddr;
  
  			srcaddr = swp_pager_meta_ctl(
  			    srcobject, 
  			    i + offset,
  			    SWM_POP
  			);
  
  			if (srcaddr != SWAPBLK_NONE) {
  				/*
  				 * swp_pager_meta_build() can sleep.
  				 */
  				vm_object_pip_add(srcobject, 1);
  				VM_OBJECT_UNLOCK(srcobject);
  				vm_object_pip_add(dstobject, 1);
  				swp_pager_meta_build(dstobject, i, srcaddr);
  				vm_object_pip_wakeup(dstobject);
  				VM_OBJECT_LOCK(srcobject);
  				vm_object_pip_wakeup(srcobject);
  			}
  		} else {
  			/*
  			 * Destination has valid swapblk or it is represented
  			 * by a resident page.  We destroy the sourceblock.
  			 */
  			
  			swp_pager_meta_ctl(srcobject, i + offset, SWM_FREE);
  		}
  	}
  
  	/*
  	 * Free left over swap blocks in source.
  	 *
  	 * We have to revert the type to OBJT_DEFAULT so we do not accidently
  	 * double-remove the object from the swap queues.
  	 */
  	if (destroysource) {
  		swp_pager_meta_free_all(srcobject);
  		/*
  		 * Reverting the type is not necessary, the caller is going
  		 * to destroy srcobject directly, but I'm doing it here
  		 * for consistency since we've removed the object from its
  		 * queues.
  		 */
  		srcobject->type = OBJT_DEFAULT;
  	}
  }
  
  /*
   * SWAP_PAGER_HASPAGE() -	determine if we have good backing store for
   *				the requested page.
   *
   *	We determine whether good backing store exists for the requested
   *	page and return TRUE if it does, FALSE if it doesn't.
   *
   *	If TRUE, we also try to determine how much valid, contiguous backing
   *	store exists before and after the requested page within a reasonable
   *	distance.  We do not try to restrict it to the swap device stripe
   *	(that is handled in getpages/putpages).  It probably isn't worth
   *	doing here.
   */
  static boolean_t
  swap_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before, int *after)
  {
  	daddr_t blk0;
  
  	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  	/*
  	 * do we have good backing store at the requested index ?
  	 */
  	blk0 = swp_pager_meta_ctl(object, pindex, 0);
  
  	if (blk0 == SWAPBLK_NONE) {
  		if (before)
  			*before = 0;
  		if (after)
  			*after = 0;
  		return (FALSE);
  	}
  
  	/*
  	 * find backwards-looking contiguous good backing store
  	 */
  	if (before != NULL) {
  		int i;
  
  		for (i = 1; i < (SWB_NPAGES/2); ++i) {
  			daddr_t blk;
  
  			if (i > pindex)
  				break;
  			blk = swp_pager_meta_ctl(object, pindex - i, 0);
  			if (blk != blk0 - i)
  				break;
  		}
  		*before = (i - 1);
  	}
  
  	/*
  	 * find forward-looking contiguous good backing store
  	 */
  	if (after != NULL) {
  		int i;
  
  		for (i = 1; i < (SWB_NPAGES/2); ++i) {
  			daddr_t blk;
  
  			blk = swp_pager_meta_ctl(object, pindex + i, 0);
  			if (blk != blk0 + i)
  				break;
  		}
  		*after = (i - 1);
  	}
  	return (TRUE);
  }
  
  /*
   * SWAP_PAGER_PAGE_UNSWAPPED() - remove swap backing store related to page
   *
   *	This removes any associated swap backing store, whether valid or
   *	not, from the page.  
   *
   *	This routine is typically called when a page is made dirty, at
   *	which point any associated swap can be freed.  MADV_FREE also
   *	calls us in a special-case situation
   *
   *	NOTE!!!  If the page is clean and the swap was valid, the caller
   *	should make the page dirty before calling this routine.  This routine
   *	does NOT change the m->dirty status of the page.  Also: MADV_FREE
   *	depends on it.
   *
   *	This routine may not sleep.
   */
  static void
  swap_pager_unswapped(vm_page_t m)
  {
  
  	VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
  	swp_pager_meta_ctl(m->object, m->pindex, SWM_FREE);
  }
  
  /*
   * SWAP_PAGER_GETPAGES() - bring pages in from swap
   *
   *	Attempt to retrieve (m, count) pages from backing store, but make
   *	sure we retrieve at least m[reqpage].  We try to load in as large
   *	a chunk surrounding m[reqpage] as is contiguous in swap and which
   *	belongs to the same object.
   *
   *	The code is designed for asynchronous operation and 
   *	immediate-notification of 'reqpage' but tends not to be
   *	used that way.  Please do not optimize-out this algorithmic
   *	feature, I intend to improve on it in the future.
   *
   *	The parent has a single vm_object_pip_add() reference prior to
   *	calling us and we should return with the same.
   *
   *	The parent has BUSY'd the pages.  We should return with 'm'
   *	left busy, but the others adjusted.
   */
  static int
  swap_pager_getpages(vm_object_t object, vm_page_t *m, int count, int reqpage)
  {
  	struct buf *bp;
  	vm_page_t mreq;
  	int i;
  	int j;
  	daddr_t blk;
  
  	mreq = m[reqpage];
  
  	KASSERT(mreq->object == object,
  	    ("swap_pager_getpages: object mismatch %p/%p",
  	    object, mreq->object));
  
  	/*
  	 * Calculate range to retrieve.  The pages have already been assigned
  	 * their swapblks.  We require a *contiguous* range but we know it to
  	 * not span devices.   If we do not supply it, bad things
  	 * happen.  Note that blk, iblk & jblk can be SWAPBLK_NONE, but the 
  	 * loops are set up such that the case(s) are handled implicitly.
  	 *
  	 * The swp_*() calls must be made with the object locked.
  	 */
  	blk = swp_pager_meta_ctl(mreq->object, mreq->pindex, 0);
  
  	for (i = reqpage - 1; i >= 0; --i) {
  		daddr_t iblk;
  
  		iblk = swp_pager_meta_ctl(m[i]->object, m[i]->pindex, 0);
  		if (blk != iblk + (reqpage - i))
  			break;
  	}
  	++i;
  
  	for (j = reqpage + 1; j < count; ++j) {
  		daddr_t jblk;
  
  		jblk = swp_pager_meta_ctl(m[j]->object, m[j]->pindex, 0);
  		if (blk != jblk - (j - reqpage))
  			break;
  	}
  
  	/*
  	 * free pages outside our collection range.   Note: we never free
  	 * mreq, it must remain busy throughout.
  	 */
  	if (0 < i || j < count) {
  		int k;
  
  		for (k = 0; k < i; ++k)
  			swp_pager_free_nrpage(m[k]);
  		for (k = j; k < count; ++k)
  			swp_pager_free_nrpage(m[k]);
  	}
  
  	/*
  	 * Return VM_PAGER_FAIL if we have nothing to do.  Return mreq 
  	 * still busy, but the others unbusied.
  	 */
  	if (blk == SWAPBLK_NONE)
  		return (VM_PAGER_FAIL);
  
  	/*
  	 * Getpbuf() can sleep.
  	 */
  	VM_OBJECT_UNLOCK(object);
  	/*
  	 * Get a swap buffer header to perform the IO
  	 */
  	bp = getpbuf(&nsw_rcount);
  	bp->b_flags |= B_PAGING;
  
  	bp->b_iocmd = BIO_READ;
  	bp->b_iodone = swp_pager_async_iodone;
  	bp->b_rcred = crhold(thread0.td_ucred);
  	bp->b_wcred = crhold(thread0.td_ucred);
  	bp->b_blkno = blk - (reqpage - i);
  	bp->b_bcount = PAGE_SIZE * (j - i);
  	bp->b_bufsize = PAGE_SIZE * (j - i);
  	bp->b_pager.pg_reqpage = reqpage - i;
  
  	VM_OBJECT_LOCK(object);
  	{
  		int k;
  
  		for (k = i; k < j; ++k) {
  			bp->b_pages[k - i] = m[k];
  			m[k]->oflags |= VPO_SWAPINPROG;
  		}
  	}
  	bp->b_npages = j - i;
  
  	PCPU_INC(cnt.v_swapin);
  	PCPU_ADD(cnt.v_swappgsin, bp->b_npages);
  
  	/*
  	 * We still hold the lock on mreq, and our automatic completion routine
  	 * does not remove it.
  	 */
  	vm_object_pip_add(object, bp->b_npages);
  	VM_OBJECT_UNLOCK(object);
  
  	/*
  	 * perform the I/O.  NOTE!!!  bp cannot be considered valid after
  	 * this point because we automatically release it on completion.
  	 * Instead, we look at the one page we are interested in which we
  	 * still hold a lock on even through the I/O completion.
  	 *
  	 * The other pages in our m[] array are also released on completion,
  	 * so we cannot assume they are valid anymore either.
  	 *
  	 * NOTE: b_blkno is destroyed by the call to swapdev_strategy
  	 */
  	BUF_KERNPROC(bp);
  	swp_pager_strategy(bp);
  
  	/*
  	 * wait for the page we want to complete.  VPO_SWAPINPROG is always
  	 * cleared on completion.  If an I/O error occurs, SWAPBLK_NONE
  	 * is set in the meta-data.
  	 */
  	VM_OBJECT_LOCK(object);
  	while ((mreq->oflags & VPO_SWAPINPROG) != 0) {
  		mreq->oflags |= VPO_WANTED;
  		PCPU_INC(cnt.v_intrans);
  		if (msleep(mreq, VM_OBJECT_MTX(object), PSWP, "swread", hz*20)) {
  			printf(
  "swap_pager: indefinite wait buffer: bufobj: %p, blkno: %jd, size: %ld\n",
  			    bp->b_bufobj, (intmax_t)bp->b_blkno, bp->b_bcount);
  		}
  	}
  
  	/*
  	 * mreq is left busied after completion, but all the other pages
  	 * are freed.  If we had an unrecoverable read error the page will
  	 * not be valid.
  	 */
  	if (mreq->valid != VM_PAGE_BITS_ALL) {
  		return (VM_PAGER_ERROR);
  	} else {
  		return (VM_PAGER_OK);
  	}
  
  	/*
  	 * A final note: in a low swap situation, we cannot deallocate swap
  	 * and mark a page dirty here because the caller is likely to mark
  	 * the page clean when we return, causing the page to possibly revert 
  	 * to all-zero's later.
  	 */
  }
  
  /*
   *	swap_pager_putpages: 
   *
   *	Assign swap (if necessary) and initiate I/O on the specified pages.
   *
   *	We support both OBJT_DEFAULT and OBJT_SWAP objects.  DEFAULT objects
   *	are automatically converted to SWAP objects.
   *
   *	In a low memory situation we may block in VOP_STRATEGY(), but the new 
   *	vm_page reservation system coupled with properly written VFS devices 
   *	should ensure that no low-memory deadlock occurs.  This is an area
   *	which needs work.
   *
   *	The parent has N vm_object_pip_add() references prior to
   *	calling us and will remove references for rtvals[] that are
   *	not set to VM_PAGER_PEND.  We need to remove the rest on I/O
   *	completion.
   *
   *	The parent has soft-busy'd the pages it passes us and will unbusy
   *	those whos rtvals[] entry is not set to VM_PAGER_PEND on return.
   *	We need to unbusy the rest on I/O completion.
   */
  void
  swap_pager_putpages(vm_object_t object, vm_page_t *m, int count,
      boolean_t sync, int *rtvals)
  {
  	int i;
  	int n = 0;
  
  	if (count && m[0]->object != object) {
  		panic("swap_pager_putpages: object mismatch %p/%p", 
  		    object, 
  		    m[0]->object
  		);
  	}
  
  	/*
  	 * Step 1
  	 *
  	 * Turn object into OBJT_SWAP
  	 * check for bogus sysops
  	 * force sync if not pageout process
  	 */
  	if (object->type != OBJT_SWAP)
  		swp_pager_meta_build(object, 0, SWAPBLK_NONE);
  	VM_OBJECT_UNLOCK(object);
  
  	if (curproc != pageproc)
  		sync = TRUE;
  
  	/*
  	 * Step 2
  	 *
  	 * Update nsw parameters from swap_async_max sysctl values.  
  	 * Do not let the sysop crash the machine with bogus numbers.
  	 */
  	mtx_lock(&pbuf_mtx);
  	if (swap_async_max != nsw_wcount_async_max) {
  		int n;
  
  		/*
  		 * limit range
  		 */
  		if ((n = swap_async_max) > nswbuf / 2)
  			n = nswbuf / 2;
  		if (n < 1)
  			n = 1;
  		swap_async_max = n;
  
  		/*
  		 * Adjust difference ( if possible ).  If the current async
  		 * count is too low, we may not be able to make the adjustment
  		 * at this time.
  		 */
  		n -= nsw_wcount_async_max;
  		if (nsw_wcount_async + n >= 0) {
  			nsw_wcount_async += n;
  			nsw_wcount_async_max += n;
  			wakeup(&nsw_wcount_async);
  		}
  	}
  	mtx_unlock(&pbuf_mtx);
  
  	/*
  	 * Step 3
  	 *
  	 * Assign swap blocks and issue I/O.  We reallocate swap on the fly.
  	 * The page is left dirty until the pageout operation completes
  	 * successfully.
  	 */
  	for (i = 0; i < count; i += n) {
  		int j;
  		struct buf *bp;
  		daddr_t blk;
  
  		/*
  		 * Maximum I/O size is limited by a number of factors.
  		 */
  		n = min(BLIST_MAX_ALLOC, count - i);
  		n = min(n, nsw_cluster_max);
  
  		/*
  		 * Get biggest block of swap we can.  If we fail, fall
  		 * back and try to allocate a smaller block.  Don't go
  		 * overboard trying to allocate space if it would overly
  		 * fragment swap.
  		 */
  		while (
  		    (blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE &&
  		    n > 4
  		) {
  			n >>= 1;
  		}
  		if (blk == SWAPBLK_NONE) {
  			for (j = 0; j < n; ++j)
  				rtvals[i+j] = VM_PAGER_FAIL;
  			continue;
  		}
  
  		/*
  		 * All I/O parameters have been satisfied, build the I/O
  		 * request and assign the swap space.
  		 */
  		if (sync == TRUE) {
  			bp = getpbuf(&nsw_wcount_sync);
  		} else {
  			bp = getpbuf(&nsw_wcount_async);
  			bp->b_flags = B_ASYNC;
  		}
  		bp->b_flags |= B_PAGING;
  		bp->b_iocmd = BIO_WRITE;
  
  		bp->b_rcred = crhold(thread0.td_ucred);
  		bp->b_wcred = crhold(thread0.td_ucred);
  		bp->b_bcount = PAGE_SIZE * n;
  		bp->b_bufsize = PAGE_SIZE * n;
  		bp->b_blkno = blk;
  
  		VM_OBJECT_LOCK(object);
  		for (j = 0; j < n; ++j) {
  			vm_page_t mreq = m[i+j];
  
  			swp_pager_meta_build(
  			    mreq->object, 
  			    mreq->pindex,
  			    blk + j
  			);
  			vm_page_dirty(mreq);
  			rtvals[i+j] = VM_PAGER_OK;
  
  			mreq->oflags |= VPO_SWAPINPROG;
  			bp->b_pages[j] = mreq;
  		}
  		VM_OBJECT_UNLOCK(object);
  		bp->b_npages = n;
  		/*
  		 * Must set dirty range for NFS to work.
  		 */
  		bp->b_dirtyoff = 0;
  		bp->b_dirtyend = bp->b_bcount;
  
  		PCPU_INC(cnt.v_swapout);
  		PCPU_ADD(cnt.v_swappgsout, bp->b_npages);
  
  		/*
  		 * asynchronous
  		 *
  		 * NOTE: b_blkno is destroyed by the call to swapdev_strategy
  		 */
  		if (sync == FALSE) {
  			bp->b_iodone = swp_pager_async_iodone;
  			BUF_KERNPROC(bp);
  			swp_pager_strategy(bp);
  
  			for (j = 0; j < n; ++j)
  				rtvals[i+j] = VM_PAGER_PEND;
  			/* restart outter loop */
  			continue;
  		}
  
  		/*
  		 * synchronous
  		 *
  		 * NOTE: b_blkno is destroyed by the call to swapdev_strategy
  		 */
  		bp->b_iodone = bdone;
  		swp_pager_strategy(bp);
  
  		/*
  		 * Wait for the sync I/O to complete, then update rtvals.
  		 * We just set the rtvals[] to VM_PAGER_PEND so we can call
  		 * our async completion routine at the end, thus avoiding a
  		 * double-free.
  		 */
  		bwait(bp, PVM, "swwrt");
  		for (j = 0; j < n; ++j)
  			rtvals[i+j] = VM_PAGER_PEND;
  		/*
  		 * Now that we are through with the bp, we can call the
  		 * normal async completion, which frees everything up.
  		 */
  		swp_pager_async_iodone(bp);
  	}
  	VM_OBJECT_LOCK(object);
  }
  
  /*
   *	swp_pager_async_iodone:
   *
   *	Completion routine for asynchronous reads and writes from/to swap.
   *	Also called manually by synchronous code to finish up a bp.
   *
   *	For READ operations, the pages are VPO_BUSY'd.  For WRITE operations, 
   *	the pages are vm_page_t->busy'd.  For READ operations, we VPO_BUSY 
   *	unbusy all pages except the 'main' request page.  For WRITE 
   *	operations, we vm_page_t->busy'd unbusy all pages ( we can do this 
   *	because we marked them all VM_PAGER_PEND on return from putpages ).
   *
   *	This routine may not sleep.
   */
  static void
  swp_pager_async_iodone(struct buf *bp)
  {
  	int i;
  	vm_object_t object = NULL;
  
  	/*
  	 * report error
  	 */
  	if (bp->b_ioflags & BIO_ERROR) {
  		printf(
  		    "swap_pager: I/O error - %s failed; blkno %ld,"
  			"size %ld, error %d\n",
  		    ((bp->b_iocmd == BIO_READ) ? "pagein" : "pageout"),
  		    (long)bp->b_blkno, 
  		    (long)bp->b_bcount,
  		    bp->b_error
  		);
  	}
  
  	/*
  	 * remove the mapping for kernel virtual
  	 */
  	if ((bp->b_flags & B_UNMAPPED) != 0) {
  		bp->b_data = bp->b_kvaalloc;
  		bp->b_kvabase = bp->b_kvaalloc;
  		bp->b_flags &= ~B_UNMAPPED;
  	} else
  		pmap_qremove((vm_offset_t)bp->b_data, bp->b_npages);
  
  	if (bp->b_npages) {
  		object = bp->b_pages[0]->object;
  		VM_OBJECT_LOCK(object);
  	}
  
  	/*
  	 * cleanup pages.  If an error occurs writing to swap, we are in
  	 * very serious trouble.  If it happens to be a disk error, though,
  	 * we may be able to recover by reassigning the swap later on.  So
  	 * in this case we remove the m->swapblk assignment for the page 
  	 * but do not free it in the rlist.  The errornous block(s) are thus
  	 * never reallocated as swap.  Redirty the page and continue.
  	 */
  	for (i = 0; i < bp->b_npages; ++i) {
  		vm_page_t m = bp->b_pages[i];
  
  		m->oflags &= ~VPO_SWAPINPROG;
  
  		if (bp->b_ioflags & BIO_ERROR) {
  			/*
  			 * If an error occurs I'd love to throw the swapblk
  			 * away without freeing it back to swapspace, so it
  			 * can never be used again.  But I can't from an 
  			 * interrupt.
  			 */
  			if (bp->b_iocmd == BIO_READ) {
  				/*
  				 * When reading, reqpage needs to stay
  				 * locked for the parent, but all other
  				 * pages can be freed.  We still want to
  				 * wakeup the parent waiting on the page,
  				 * though.  ( also: pg_reqpage can be -1 and 
  				 * not match anything ).
  				 *
  				 * We have to wake specifically requested pages
  				 * up too because we cleared VPO_SWAPINPROG and
  				 * someone may be waiting for that.
  				 *
  				 * NOTE: for reads, m->dirty will probably
  				 * be overridden by the original caller of
  				 * getpages so don't play cute tricks here.
  				 */
  				m->valid = 0;
  				if (i != bp->b_pager.pg_reqpage)
  					swp_pager_free_nrpage(m);
  				else
  					vm_page_flash(m);
  				/*
  				 * If i == bp->b_pager.pg_reqpage, do not wake 
  				 * the page up.  The caller needs to.
  				 */
  			} else {
  				/*
  				 * If a write error occurs, reactivate page
  				 * so it doesn't clog the inactive list,
  				 * then finish the I/O.
  				 */
  				vm_page_dirty(m);
  				vm_page_lock(m);
  				vm_page_activate(m);
  				vm_page_unlock(m);
  				vm_page_io_finish(m);
  			}
  		} else if (bp->b_iocmd == BIO_READ) {
  			/*
  			 * NOTE: for reads, m->dirty will probably be 
  			 * overridden by the original caller of getpages so
  			 * we cannot set them in order to free the underlying
  			 * swap in a low-swap situation.  I don't think we'd
  			 * want to do that anyway, but it was an optimization
  			 * that existed in the old swapper for a time before
  			 * it got ripped out due to precisely this problem.
  			 *
  			 * If not the requested page then deactivate it.
  			 *
  			 * Note that the requested page, reqpage, is left
  			 * busied, but we still have to wake it up.  The
  			 * other pages are released (unbusied) by 
  			 * vm_page_wakeup().
  			 */
  			KASSERT(!pmap_page_is_mapped(m),
  			    ("swp_pager_async_iodone: page %p is mapped", m));
  			m->valid = VM_PAGE_BITS_ALL;
  			KASSERT(m->dirty == 0,
  			    ("swp_pager_async_iodone: page %p is dirty", m));
  
  			/*
  			 * We have to wake specifically requested pages
  			 * up too because we cleared VPO_SWAPINPROG and
  			 * could be waiting for it in getpages.  However,
  			 * be sure to not unbusy getpages specifically
  			 * requested page - getpages expects it to be 
  			 * left busy.
  			 */
  			if (i != bp->b_pager.pg_reqpage) {
  				vm_page_lock(m);
  				vm_page_deactivate(m);
  				vm_page_unlock(m);
  				vm_page_wakeup(m);
  			} else
  				vm_page_flash(m);
  		} else {
  			/*
  			 * For write success, clear the dirty
  			 * status, then finish the I/O ( which decrements the 
  			 * busy count and possibly wakes waiter's up ).
  			 */
  			KASSERT(!pmap_page_is_write_mapped(m),
  			    ("swp_pager_async_iodone: page %p is not write"
  			    " protected", m));
  			vm_page_undirty(m);
  			vm_page_io_finish(m);
  			if (vm_page_count_severe()) {
  				vm_page_lock(m);
  				vm_page_try_to_cache(m);
  				vm_page_unlock(m);
  			}
  		}
  	}
  
  	/*
  	 * adjust pip.  NOTE: the original parent may still have its own
  	 * pip refs on the object.
  	 */
  	if (object != NULL) {
  		vm_object_pip_wakeupn(object, bp->b_npages);
  		VM_OBJECT_UNLOCK(object);
  	}
  
  	/* 
  	 * swapdev_strategy() manually sets b_vp and b_bufobj before calling 
  	 * bstrategy(). Set them back to NULL now we're done with it, or we'll
  	 * trigger a KASSERT in relpbuf().
  	 */
  	if (bp->b_vp) {
  		    bp->b_vp = NULL;
  		    bp->b_bufobj = NULL;
  	}
  	/*
  	 * release the physical I/O buffer
  	 */
  	relpbuf(
  	    bp, 
  	    ((bp->b_iocmd == BIO_READ) ? &nsw_rcount : 
  		((bp->b_flags & B_ASYNC) ? 
  		    &nsw_wcount_async : 
  		    &nsw_wcount_sync
  		)
  	    )
  	);
  }
  
  /*
   *	swap_pager_isswapped:
   *
   *	Return 1 if at least one page in the given object is paged
   *	out to the given swap device.
   *
   *	This routine may not sleep.
   */
  int
  swap_pager_isswapped(vm_object_t object, struct swdevt *sp)
  {
  	daddr_t index = 0;
  	int bcount;
  	int i;
  
  	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  	if (object->type != OBJT_SWAP)
  		return (0);
  
  	mtx_lock(&swhash_mtx);
  	for (bcount = 0; bcount < object->un_pager.swp.swp_bcount; bcount++) {
  		struct swblock *swap;
  
  		if ((swap = *swp_pager_hash(object, index)) != NULL) {
  			for (i = 0; i < SWAP_META_PAGES; ++i) {
  				if (swp_pager_isondev(swap->swb_pages[i], sp)) {
  					mtx_unlock(&swhash_mtx);
  					return (1);
  				}
  			}
  		}
  		index += SWAP_META_PAGES;
  	}
  	mtx_unlock(&swhash_mtx);
  	return (0);
  }
  
  /*
   * SWP_PAGER_FORCE_PAGEIN() - force a swap block to be paged in
   *
   *	This routine dissociates the page at the given index within a
   *	swap block from its backing store, paging it in if necessary.
   *	If the page is paged in, it is placed in the inactive queue,
   *	since it had its backing store ripped out from under it.
   *	We also attempt to swap in all other pages in the swap block,
   *	we only guarantee that the one at the specified index is
   *	paged in.
   *
   *	XXX - The code to page the whole block in doesn't work, so we
   *	      revert to the one-by-one behavior for now.  Sigh.
   */
  static inline void
  swp_pager_force_pagein(vm_object_t object, vm_pindex_t pindex)
  {
  	vm_page_t m;
  
  	vm_object_pip_add(object, 1);
  	m = vm_page_grab(object, pindex, VM_ALLOC_NORMAL|VM_ALLOC_RETRY);
  	if (m->valid == VM_PAGE_BITS_ALL) {
  		vm_object_pip_subtract(object, 1);
  		vm_page_dirty(m);
  		vm_page_lock(m);
  		vm_page_activate(m);
  		vm_page_unlock(m);
  		vm_page_wakeup(m);
  		vm_pager_page_unswapped(m);
  		return;
  	}
  
  	if (swap_pager_getpages(object, &m, 1, 0) != VM_PAGER_OK)
  		panic("swap_pager_force_pagein: read from swap failed");/*XXX*/
  	vm_object_pip_subtract(object, 1);
  	vm_page_dirty(m);
  	vm_page_lock(m);
  	vm_page_deactivate(m);
  	vm_page_unlock(m);
  	vm_page_wakeup(m);
  	vm_pager_page_unswapped(m);
  }
  
  /*
   *	swap_pager_swapoff:
   *
   *	Page in all of the pages that have been paged out to the
   *	given device.  The corresponding blocks in the bitmap must be
   *	marked as allocated and the device must be flagged SW_CLOSING.
   *	There may be no processes swapped out to the device.
   *
   *	This routine may block.
   */
  static void
  swap_pager_swapoff(struct swdevt *sp)
  {
  	struct swblock *swap;
  	int i, j, retries;
  
  	GIANT_REQUIRED;
  
  	retries = 0;
  full_rescan:
  	mtx_lock(&swhash_mtx);
  	for (i = 0; i <= swhash_mask; i++) { /* '<=' is correct here */
  restart:
  		for (swap = swhash[i]; swap != NULL; swap = swap->swb_hnext) {
  			vm_object_t object = swap->swb_object;
  			vm_pindex_t pindex = swap->swb_index;
                          for (j = 0; j < SWAP_META_PAGES; ++j) {
                                  if (swp_pager_isondev(swap->swb_pages[j], sp)) {
  					/* avoid deadlock */
  					if (!VM_OBJECT_TRYLOCK(object)) {
  						break;
  					} else {
  						mtx_unlock(&swhash_mtx);
  						swp_pager_force_pagein(object,
  						    pindex + j);
  						VM_OBJECT_UNLOCK(object);
  						mtx_lock(&swhash_mtx);
  						goto restart;
  					}
  				}
                          }
  		}
  	}
  	mtx_unlock(&swhash_mtx);
  	if (sp->sw_used) {
  		/*
  		 * Objects may be locked or paging to the device being
  		 * removed, so we will miss their pages and need to
  		 * make another pass.  We have marked this device as
  		 * SW_CLOSING, so the activity should finish soon.
  		 */
  		retries++;
  		if (retries > 100) {
  			panic("swapoff: failed to locate %d swap blocks",
  			    sp->sw_used);
  		}
  		pause("swpoff", hz / 20);
  		goto full_rescan;
  	}
  }
  
  /************************************************************************
   *				SWAP META DATA 				*
   ************************************************************************
   *
   *	These routines manipulate the swap metadata stored in the 
   *	OBJT_SWAP object.
   *
   *	Swap metadata is implemented with a global hash and not directly
   *	linked into the object.  Instead the object simply contains
   *	appropriate tracking counters.
   */
  
  /*
   * SWP_PAGER_META_BUILD() -	add swap block to swap meta data for object
   *
   *	We first convert the object to a swap object if it is a default
   *	object.
   *
   *	The specified swapblk is added to the object's swap metadata.  If
   *	the swapblk is not valid, it is freed instead.  Any previously
   *	assigned swapblk is freed.
   */
  static void
  swp_pager_meta_build(vm_object_t object, vm_pindex_t pindex, daddr_t swapblk)
  {
  	static volatile int exhausted;
  	struct swblock *swap;
  	struct swblock **pswap;
  	int idx;
  
  	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  	/*
  	 * Convert default object to swap object if necessary
  	 */
  	if (object->type != OBJT_SWAP) {
  		object->type = OBJT_SWAP;
  		object->un_pager.swp.swp_bcount = 0;
  
  		if (object->handle != NULL) {
  			mtx_lock(&sw_alloc_mtx);
  			TAILQ_INSERT_TAIL(
  			    NOBJLIST(object->handle),
  			    object, 
  			    pager_object_list
  			);
  			mtx_unlock(&sw_alloc_mtx);
  		}
  	}
  	
  	/*
  	 * Locate hash entry.  If not found create, but if we aren't adding
  	 * anything just return.  If we run out of space in the map we wait
  	 * and, since the hash table may have changed, retry.
  	 */
  retry:
  	mtx_lock(&swhash_mtx);
  	pswap = swp_pager_hash(object, pindex);
  
  	if ((swap = *pswap) == NULL) {
  		int i;
  
  		if (swapblk == SWAPBLK_NONE)
  			goto done;
  
  		swap = *pswap = uma_zalloc(swap_zone, M_NOWAIT);
  		if (swap == NULL) {
  			mtx_unlock(&swhash_mtx);
  			VM_OBJECT_UNLOCK(object);
  			if (uma_zone_exhausted(swap_zone)) {
  				if (atomic_cmpset_rel_int(&exhausted, 0, 1))
  					printf("swap zone exhausted, "
  					    "increase kern.maxswzone\n");
  				vm_pageout_oom(VM_OOM_SWAPZ);
  				pause("swzonex", 10);
  			} else
  				VM_WAIT;
  			VM_OBJECT_LOCK(object);
  			goto retry;
  		}
  
  		if (atomic_cmpset_rel_int(&exhausted, 1, 0))
  			printf("swap zone ok\n");
  
  		swap->swb_hnext = NULL;
  		swap->swb_object = object;
  		swap->swb_index = pindex & ~(vm_pindex_t)SWAP_META_MASK;
  		swap->swb_count = 0;
  
  		++object->un_pager.swp.swp_bcount;
  
  		for (i = 0; i < SWAP_META_PAGES; ++i)
  			swap->swb_pages[i] = SWAPBLK_NONE;
  	}
  
  	/*
  	 * Delete prior contents of metadata
  	 */
  	idx = pindex & SWAP_META_MASK;
  
  	if (swap->swb_pages[idx] != SWAPBLK_NONE) {
  		swp_pager_freeswapspace(swap->swb_pages[idx], 1);
  		--swap->swb_count;
  	}
  
  	/*
  	 * Enter block into metadata
  	 */
  	swap->swb_pages[idx] = swapblk;
  	if (swapblk != SWAPBLK_NONE)
  		++swap->swb_count;
  done:
  	mtx_unlock(&swhash_mtx);
  }
  
  /*
   * SWP_PAGER_META_FREE() - free a range of blocks in the object's swap metadata
   *
   *	The requested range of blocks is freed, with any associated swap 
   *	returned to the swap bitmap.
   *
   *	This routine will free swap metadata structures as they are cleaned 
   *	out.  This routine does *NOT* operate on swap metadata associated
   *	with resident pages.
   */
  static void
  swp_pager_meta_free(vm_object_t object, vm_pindex_t index, daddr_t count)
  {
  
  	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  	if (object->type != OBJT_SWAP)
  		return;
  
  	while (count > 0) {
  		struct swblock **pswap;
  		struct swblock *swap;
  
  		mtx_lock(&swhash_mtx);
  		pswap = swp_pager_hash(object, index);
  
  		if ((swap = *pswap) != NULL) {
  			daddr_t v = swap->swb_pages[index & SWAP_META_MASK];
  
  			if (v != SWAPBLK_NONE) {
  				swp_pager_freeswapspace(v, 1);
  				swap->swb_pages[index & SWAP_META_MASK] =
  					SWAPBLK_NONE;
  				if (--swap->swb_count == 0) {
  					*pswap = swap->swb_hnext;
  					uma_zfree(swap_zone, swap);
  					--object->un_pager.swp.swp_bcount;
  				}
  			}
  			--count;
  			++index;
  		} else {
  			int n = SWAP_META_PAGES - (index & SWAP_META_MASK);
  			count -= n;
  			index += n;
  		}
  		mtx_unlock(&swhash_mtx);
  	}
  }
  
  /*
   * SWP_PAGER_META_FREE_ALL() - destroy all swap metadata associated with object
   *
   *	This routine locates and destroys all swap metadata associated with
   *	an object.
   */
  static void
  swp_pager_meta_free_all(vm_object_t object)
  {
  	daddr_t index = 0;
  
  	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  	if (object->type != OBJT_SWAP)
  		return;
  
  	while (object->un_pager.swp.swp_bcount) {
  		struct swblock **pswap;
  		struct swblock *swap;
  
  		mtx_lock(&swhash_mtx);
  		pswap = swp_pager_hash(object, index);
  		if ((swap = *pswap) != NULL) {
  			int i;
  
  			for (i = 0; i < SWAP_META_PAGES; ++i) {
  				daddr_t v = swap->swb_pages[i];
  				if (v != SWAPBLK_NONE) {
  					--swap->swb_count;
  					swp_pager_freeswapspace(v, 1);
  				}
  			}
  			if (swap->swb_count != 0)
  				panic("swap_pager_meta_free_all: swb_count != 0");
  			*pswap = swap->swb_hnext;
  			uma_zfree(swap_zone, swap);
  			--object->un_pager.swp.swp_bcount;
  		}
  		mtx_unlock(&swhash_mtx);
  		index += SWAP_META_PAGES;
  	}
  }
  
  /*
   * SWP_PAGER_METACTL() -  misc control of swap and vm_page_t meta data.
   *
   *	This routine is capable of looking up, popping, or freeing
   *	swapblk assignments in the swap meta data or in the vm_page_t.
   *	The routine typically returns the swapblk being looked-up, or popped,
   *	or SWAPBLK_NONE if the block was freed, or SWAPBLK_NONE if the block
   *	was invalid.  This routine will automatically free any invalid 
   *	meta-data swapblks.
   *
   *	It is not possible to store invalid swapblks in the swap meta data
   *	(other then a literal 'SWAPBLK_NONE'), so we don't bother checking.
   *
   *	When acting on a busy resident page and paging is in progress, we 
   *	have to wait until paging is complete but otherwise can act on the 
   *	busy page.
   *
   *	SWM_FREE	remove and free swap block from metadata
   *	SWM_POP		remove from meta data but do not free.. pop it out
   */
  static daddr_t
  swp_pager_meta_ctl(vm_object_t object, vm_pindex_t pindex, int flags)
  {
  	struct swblock **pswap;
  	struct swblock *swap;
  	daddr_t r1;
  	int idx;
  
  	VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  	/*
  	 * The meta data only exists of the object is OBJT_SWAP 
  	 * and even then might not be allocated yet.
  	 */
  	if (object->type != OBJT_SWAP)
  		return (SWAPBLK_NONE);
  
  	r1 = SWAPBLK_NONE;
  	mtx_lock(&swhash_mtx);
  	pswap = swp_pager_hash(object, pindex);
  
  	if ((swap = *pswap) != NULL) {
  		idx = pindex & SWAP_META_MASK;
  		r1 = swap->swb_pages[idx];
  
  		if (r1 != SWAPBLK_NONE) {
  			if (flags & SWM_FREE) {
  				swp_pager_freeswapspace(r1, 1);
  				r1 = SWAPBLK_NONE;
  			}
  			if (flags & (SWM_FREE|SWM_POP)) {
  				swap->swb_pages[idx] = SWAPBLK_NONE;
  				if (--swap->swb_count == 0) {
  					*pswap = swap->swb_hnext;
  					uma_zfree(swap_zone, swap);
  					--object->un_pager.swp.swp_bcount;
  				}
  			} 
  		}
  	}
  	mtx_unlock(&swhash_mtx);
  	return (r1);
  }
  
  /*
   * System call swapon(name) enables swapping on device name,
   * which must be in the swdevsw.  Return EBUSY
   * if already swapping on this device.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct swapon_args {
  	char *name;
  };
  #endif
  
  /* 
   * MPSAFE
   */
  /* ARGSUSED */
  int
  sys_swapon(struct thread *td, struct swapon_args *uap)
  {
  	struct vattr attr;
  	struct vnode *vp;
  	struct nameidata nd;
  	int error;
  
  	error = priv_check(td, PRIV_SWAPON);
  	if (error)
  		return (error);
  
  	mtx_lock(&Giant);
  	while (swdev_syscall_active)
  	    tsleep(&swdev_syscall_active, PUSER - 1, "swpon", 0);
  	swdev_syscall_active = 1;
  
  	/*
  	 * Swap metadata may not fit in the KVM if we have physical
  	 * memory of >1GB.
  	 */
  	if (swap_zone == NULL) {
  		error = ENOMEM;
  		goto done;
  	}
  
  	NDINIT(&nd, LOOKUP, ISOPEN | FOLLOW | AUDITVNODE1, UIO_USERSPACE,
  	    uap->name, td);
  	error = namei(&nd);
  	if (error)
  		goto done;
  
  	NDFREE(&nd, NDF_ONLY_PNBUF);
  	vp = nd.ni_vp;
  
  	if (vn_isdisk(vp, &error)) {
  		error = swapongeom(td, vp);
  	} else if (vp->v_type == VREG &&
  	    (vp->v_mount->mnt_vfc->vfc_flags & VFCF_NETWORK) != 0 &&
  	    (error = VOP_GETATTR(vp, &attr, td->td_ucred)) == 0) {
  		/*
  		 * Allow direct swapping to NFS regular files in the same
  		 * way that nfs_mountroot() sets up diskless swapping.
  		 */
  		error = swaponvp(td, vp, attr.va_size / DEV_BSIZE);
  	}
  
  	if (error)
  		vrele(vp);
  done:
  	swdev_syscall_active = 0;
  	wakeup_one(&swdev_syscall_active);
  	mtx_unlock(&Giant);
  	return (error);
  }
  
  /*
   * Check that the total amount of swap currently configured does not
   * exceed half the theoretical maximum.  If it does, print a warning
   * message and return -1; otherwise, return 0.
   */
  static int
  swapon_check_swzone(unsigned long npages)
  {
  	unsigned long maxpages;
  
  	/* absolute maximum we can handle assuming 100% efficiency */
  	maxpages = uma_zone_get_max(swap_zone) * SWAP_META_PAGES;
  
  	/* recommend using no more than half that amount */
  	if (npages > maxpages / 2) {
  		printf("warning: total configured swap (%lu pages) "
  		    "exceeds maximum recommended amount (%lu pages).\n",
  		    npages, maxpages / 2);
  		printf("warning: increase kern.maxswzone "
  		    "or reduce amount of swap.\n");
  		return (-1);
  	}
  	return (0);
  }
  
  static void
  swaponsomething(struct vnode *vp, void *id, u_long nblks,
      sw_strategy_t *strategy, sw_close_t *close, dev_t dev, int flags)
  {
  	struct swdevt *sp, *tsp;
  	swblk_t dvbase;
  	u_long mblocks;
  
  	/*
  	 * nblks is in DEV_BSIZE'd chunks, convert to PAGE_SIZE'd chunks.
  	 * First chop nblks off to page-align it, then convert.
  	 * 
  	 * sw->sw_nblks is in page-sized chunks now too.
  	 */
  	nblks &= ~(ctodb(1) - 1);
  	nblks = dbtoc(nblks);
  
  	/*
  	 * If we go beyond this, we get overflows in the radix
  	 * tree bitmap code.
  	 */
  	mblocks = 0x40000000 / BLIST_META_RADIX;
  	if (nblks > mblocks) {
  		printf(
      "WARNING: reducing swap size to maximum of %luMB per unit\n",
  		    mblocks / 1024 / 1024 * PAGE_SIZE);
  		nblks = mblocks;
  	}
  
  	sp = malloc(sizeof *sp, M_VMPGDATA, M_WAITOK | M_ZERO);
  	sp->sw_vp = vp;
  	sp->sw_id = id;
  	sp->sw_dev = dev;
  	sp->sw_flags = 0;
  	sp->sw_nblks = nblks;
  	sp->sw_used = 0;
  	sp->sw_strategy = strategy;
  	sp->sw_close = close;
  	sp->sw_flags = flags;
  
  	sp->sw_blist = blist_create(nblks, M_WAITOK);
  	/*
  	 * Do not free the first two block in order to avoid overwriting
  	 * any bsd label at the front of the partition
  	 */
  	blist_free(sp->sw_blist, 2, nblks - 2);
  
  	dvbase = 0;
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(tsp, &swtailq, sw_list) {
  		if (tsp->sw_end >= dvbase) {
  			/*
  			 * We put one uncovered page between the devices
  			 * in order to definitively prevent any cross-device
  			 * I/O requests
  			 */
  			dvbase = tsp->sw_end + 1;
  		}
  	}
  	sp->sw_first = dvbase;
  	sp->sw_end = dvbase + nblks;
  	TAILQ_INSERT_TAIL(&swtailq, sp, sw_list);
  	nswapdev++;
  	swap_pager_avail += nblks;
  	swap_total += (vm_ooffset_t)nblks * PAGE_SIZE;
  	swapon_check_swzone(swap_total / PAGE_SIZE);
  	swp_sizecheck();
  	mtx_unlock(&sw_dev_mtx);
  }
  
  /*
   * SYSCALL: swapoff(devname)
   *
   * Disable swapping on the given device.
   *
   * XXX: Badly designed system call: it should use a device index
   * rather than filename as specification.  We keep sw_vp around
   * only to make this work.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct swapoff_args {
  	char *name;
  };
  #endif
  
  /*
   * MPSAFE
   */
  /* ARGSUSED */
  int
  sys_swapoff(struct thread *td, struct swapoff_args *uap)
  {
  	struct vnode *vp;
  	struct nameidata nd;
  	struct swdevt *sp;
  	int error;
  
  	error = priv_check(td, PRIV_SWAPOFF);
  	if (error)
  		return (error);
  
  	mtx_lock(&Giant);
  	while (swdev_syscall_active)
  	    tsleep(&swdev_syscall_active, PUSER - 1, "swpoff", 0);
  	swdev_syscall_active = 1;
  
  	NDINIT(&nd, LOOKUP, FOLLOW | AUDITVNODE1, UIO_USERSPACE, uap->name,
  	    td);
  	error = namei(&nd);
  	if (error)
  		goto done;
  	NDFREE(&nd, NDF_ONLY_PNBUF);
  	vp = nd.ni_vp;
  
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(sp, &swtailq, sw_list) {
  		if (sp->sw_vp == vp)
  			break;
  	}
  	mtx_unlock(&sw_dev_mtx);
  	if (sp == NULL) {
  		error = EINVAL;
  		goto done;
  	}
  	error = swapoff_one(sp, td->td_ucred);
  done:
  	swdev_syscall_active = 0;
  	wakeup_one(&swdev_syscall_active);
  	mtx_unlock(&Giant);
  	return (error);
  }
  
  static int
  swapoff_one(struct swdevt *sp, struct ucred *cred)
  {
  	u_long nblks, dvbase;
  #ifdef MAC
  	int error;
  #endif
  
  	mtx_assert(&Giant, MA_OWNED);
  #ifdef MAC
  	(void) vn_lock(sp->sw_vp, LK_EXCLUSIVE | LK_RETRY);
  	error = mac_system_check_swapoff(cred, sp->sw_vp);
  	(void) VOP_UNLOCK(sp->sw_vp, 0);
  	if (error != 0)
  		return (error);
  #endif
  	nblks = sp->sw_nblks;
  
  	/*
  	 * We can turn off this swap device safely only if the
  	 * available virtual memory in the system will fit the amount
  	 * of data we will have to page back in, plus an epsilon so
  	 * the system doesn't become critically low on swap space.
  	 */
  	if (cnt.v_free_count + cnt.v_cache_count + swap_pager_avail <
  	    nblks + nswap_lowat) {
  		return (ENOMEM);
  	}
  
  	/*
  	 * Prevent further allocations on this device.
  	 */
  	mtx_lock(&sw_dev_mtx);
  	sp->sw_flags |= SW_CLOSING;
  	for (dvbase = 0; dvbase < sp->sw_end; dvbase += dmmax) {
  		swap_pager_avail -= blist_fill(sp->sw_blist,
  		     dvbase, dmmax);
  	}
  	swap_total -= (vm_ooffset_t)nblks * PAGE_SIZE;
  	mtx_unlock(&sw_dev_mtx);
  
  	/*
  	 * Page in the contents of the device and close it.
  	 */
  	swap_pager_swapoff(sp);
  
  	sp->sw_close(curthread, sp);
  	sp->sw_id = NULL;
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_REMOVE(&swtailq, sp, sw_list);
  	nswapdev--;
  	if (nswapdev == 0) {
  		swap_pager_full = 2;
  		swap_pager_almost_full = 1;
  	}
  	if (swdevhd == sp)
  		swdevhd = NULL;
  	mtx_unlock(&sw_dev_mtx);
  	blist_destroy(sp->sw_blist);
  	free(sp, M_VMPGDATA);
  	return (0);
  }
  
  void
  swapoff_all(void)
  {
  	struct swdevt *sp, *spt;
  	const char *devname;
  	int error;
   
  	mtx_lock(&Giant);
  	while (swdev_syscall_active)
  		tsleep(&swdev_syscall_active, PUSER - 1, "swpoff", 0);
  	swdev_syscall_active = 1;
   
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH_SAFE(sp, &swtailq, sw_list, spt) {
  		mtx_unlock(&sw_dev_mtx);
  		if (vn_isdisk(sp->sw_vp, NULL))
  			devname = devtoname(sp->sw_vp->v_rdev);
  		else
  			devname = "[file]";
  		error = swapoff_one(sp, thread0.td_ucred);
  		if (error != 0) {
  			printf("Cannot remove swap device %s (error=%d), "
  			    "skipping.\n", devname, error);
  		} else if (bootverbose) {
  			printf("Swap device %s removed.\n", devname);
  		}
  		mtx_lock(&sw_dev_mtx);
  	}
  	mtx_unlock(&sw_dev_mtx);
   
  	swdev_syscall_active = 0;
  	wakeup_one(&swdev_syscall_active);
  	mtx_unlock(&Giant);
  }
  
  void
  swap_pager_status(int *total, int *used)
  {
  	struct swdevt *sp;
  
  	*total = 0;
  	*used = 0;
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(sp, &swtailq, sw_list) {
  		*total += sp->sw_nblks;
  		*used += sp->sw_used;
  	}
  	mtx_unlock(&sw_dev_mtx);
  }
  
  int
  swap_dev_info(int name, struct xswdev *xs, char *devname, size_t len)
  {
  	struct swdevt *sp;
  	const char *tmp_devname;
  	int error, n;
  
  	n = 0;
  	error = ENOENT;
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(sp, &swtailq, sw_list) {
  		if (n != name) {
  			n++;
  			continue;
  		}
  		xs->xsw_version = XSWDEV_VERSION;
  		xs->xsw_dev = sp->sw_dev;
  		xs->xsw_flags = sp->sw_flags;
  		xs->xsw_nblks = sp->sw_nblks;
  		xs->xsw_used = sp->sw_used;
  		if (devname != NULL) {
  			if (vn_isdisk(sp->sw_vp, NULL))
  				tmp_devname = devtoname(sp->sw_vp->v_rdev);
  			else
  				tmp_devname = "[file]";
  			strncpy(devname, tmp_devname, len);
  		}
  		error = 0;
  		break;
  	}
  	mtx_unlock(&sw_dev_mtx);
  	return (error);
  }
  
  static int
  sysctl_vm_swap_info(SYSCTL_HANDLER_ARGS)
  {
  	struct xswdev xs;
  	int error;
  
  	if (arg2 != 1)			/* name length */
  		return (EINVAL);
  	error = swap_dev_info(*(int *)arg1, &xs, NULL, 0);
  	if (error != 0)
  		return (error);
  	error = SYSCTL_OUT(req, &xs, sizeof(xs));
  	return (error);
  }
  
  SYSCTL_INT(_vm, OID_AUTO, nswapdev, CTLFLAG_RD, &nswapdev, 0,
      "Number of swap devices");
  SYSCTL_NODE(_vm, OID_AUTO, swap_info, CTLFLAG_RD, sysctl_vm_swap_info,
      "Swap statistics by device");
  
  /*
   * vmspace_swap_count() - count the approximate swap usage in pages for a
   *			  vmspace.
   *
   *	The map must be locked.
   *
   *	Swap usage is determined by taking the proportional swap used by
   *	VM objects backing the VM map.  To make up for fractional losses,
   *	if the VM object has any swap use at all the associated map entries
   *	count for at least 1 swap page.
   */
  long
  vmspace_swap_count(struct vmspace *vmspace)
  {
  	vm_map_t map;
  	vm_map_entry_t cur;
  	vm_object_t object;
  	long count, n;
  
  	map = &vmspace->vm_map;
  	count = 0;
  
  	for (cur = map->header.next; cur != &map->header; cur = cur->next) {
  		if ((cur->eflags & MAP_ENTRY_IS_SUB_MAP) == 0 &&
  		    (object = cur->object.vm_object) != NULL) {
  			VM_OBJECT_LOCK(object);
  			if (object->type == OBJT_SWAP &&
  			    object->un_pager.swp.swp_bcount != 0) {
  				n = (cur->end - cur->start) / PAGE_SIZE;
  				count += object->un_pager.swp.swp_bcount *
  				    SWAP_META_PAGES * n / object->size + 1;
  			}
  			VM_OBJECT_UNLOCK(object);
  		}
  	}
  	return (count);
  }
  
  /*
   * GEOM backend
   *
   * Swapping onto disk devices.
   *
   */
  
  static g_orphan_t swapgeom_orphan;
  
  static struct g_class g_swap_class = {
  	.name = "SWAP",
  	.version = G_VERSION,
  	.orphan = swapgeom_orphan,
  };
  
  DECLARE_GEOM_CLASS(g_swap_class, g_class);
  
  
  static void
  swapgeom_done(struct bio *bp2)
  {
  	struct buf *bp;
  
  	bp = bp2->bio_caller2;
  	bp->b_ioflags = bp2->bio_flags;
  	if (bp2->bio_error)
  		bp->b_ioflags |= BIO_ERROR;
  	bp->b_resid = bp->b_bcount - bp2->bio_completed;
  	bp->b_error = bp2->bio_error;
  	bufdone(bp);
  	g_destroy_bio(bp2);
  }
  
  static void
  swapgeom_strategy(struct buf *bp, struct swdevt *sp)
  {
  	struct bio *bio;
  	struct g_consumer *cp;
  
  	cp = sp->sw_id;
  	if (cp == NULL) {
  		bp->b_error = ENXIO;
  		bp->b_ioflags |= BIO_ERROR;
  		bufdone(bp);
  		return;
  	}
  	if (bp->b_iocmd == BIO_WRITE)
  		bio = g_new_bio();
  	else
  		bio = g_alloc_bio();
  	if (bio == NULL) {
  		bp->b_error = ENOMEM;
  		bp->b_ioflags |= BIO_ERROR;
  		bufdone(bp);
  		return;
  	}
  
  	bio->bio_caller2 = bp;
  	bio->bio_cmd = bp->b_iocmd;
  	bio->bio_offset = (bp->b_blkno - sp->sw_first) * PAGE_SIZE;
  	bio->bio_length = bp->b_bcount;
  	bio->bio_done = swapgeom_done;
  	if ((bp->b_flags & B_UNMAPPED) != 0) {
  		bio->bio_ma = bp->b_pages;
  		bio->bio_data = unmapped_buf;
  		bio->bio_ma_offset = (vm_offset_t)bp->b_offset & PAGE_MASK;
  		bio->bio_ma_n = bp->b_npages;
  		bio->bio_flags |= BIO_UNMAPPED;
  	} else {
  		bio->bio_data = bp->b_data;
  		bio->bio_ma = NULL;
  	}
  	g_io_request(bio, cp);
  	return;
  }
  
  static void
  swapgeom_orphan(struct g_consumer *cp)
  {
  	struct swdevt *sp;
  
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(sp, &swtailq, sw_list)
  		if (sp->sw_id == cp)
  			sp->sw_flags |= SW_CLOSING;
  	mtx_unlock(&sw_dev_mtx);
  }
  
  static void
  swapgeom_close_ev(void *arg, int flags)
  {
  	struct g_consumer *cp;
  
  	cp = arg;
  	g_access(cp, -1, -1, 0);
  	g_detach(cp);
  	g_destroy_consumer(cp);
  }
  
  static void
  swapgeom_close(struct thread *td, struct swdevt *sw)
  {
  
  	/* XXX: direct call when Giant untangled */
  	g_waitfor_event(swapgeom_close_ev, sw->sw_id, M_WAITOK, NULL);
  }
  
  
  struct swh0h0 {
  	struct cdev *dev;
  	struct vnode *vp;
  	int	error;
  };
  
  static void
  swapongeom_ev(void *arg, int flags)
  {
  	struct swh0h0 *swh;
  	struct g_provider *pp;
  	struct g_consumer *cp;
  	static struct g_geom *gp;
  	struct swdevt *sp;
  	u_long nblks;
  	int error;
  
  	swh = arg;
  	swh->error = 0;
  	pp = g_dev_getprovider(swh->dev);
  	if (pp == NULL) {
  		swh->error = ENODEV;
  		return;
  	}
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(sp, &swtailq, sw_list) {
  		cp = sp->sw_id;
  		if (cp != NULL && cp->provider == pp) {
  			mtx_unlock(&sw_dev_mtx);
  			swh->error = EBUSY;
  			return;
  		}
  	}
  	mtx_unlock(&sw_dev_mtx);
  	if (gp == NULL)
  		gp = g_new_geomf(&g_swap_class, "swap");
  	cp = g_new_consumer(gp);
  	g_attach(cp, pp);
  	/*
  	 * XXX: Everytime you think you can improve the margin for
  	 * footshooting, somebody depends on the ability to do so:
  	 * savecore(8) wants to write to our swapdev so we cannot
  	 * set an exclusive count :-(
  	 */
  	error = g_access(cp, 1, 1, 0);
  	if (error) {
  		g_detach(cp);
  		g_destroy_consumer(cp);
  		swh->error = error;
  		return;
  	}
  	nblks = pp->mediasize / DEV_BSIZE;
  	swaponsomething(swh->vp, cp, nblks, swapgeom_strategy,
  	    swapgeom_close, dev2udev(swh->dev),
  	    (pp->flags & G_PF_ACCEPT_UNMAPPED) != 0 ? SW_UNMAPPED : 0);
  	swh->error = 0;
  }
  
  static int
  swapongeom(struct thread *td, struct vnode *vp)
  {
  	int error;
  	struct swh0h0 swh;
  
  	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
  
  	swh.dev = vp->v_rdev;
  	swh.vp = vp;
  	swh.error = 0;
  	/* XXX: direct call when Giant untangled */
  	error = g_waitfor_event(swapongeom_ev, &swh, M_WAITOK, NULL);
  	if (!error)
  		error = swh.error;
  	VOP_UNLOCK(vp, 0);
  	return (error);
  }
  
  /*
   * VNODE backend
   *
   * This is used mainly for network filesystem (read: probably only tested
   * with NFS) swapfiles.
   *
   */
  
  static void
  swapdev_strategy(struct buf *bp, struct swdevt *sp)
  {
  	struct vnode *vp2;
  
  	bp->b_blkno = ctodb(bp->b_blkno - sp->sw_first);
  
  	vp2 = sp->sw_id;
  	vhold(vp2);
  	if (bp->b_iocmd == BIO_WRITE) {
  		if (bp->b_bufobj)
  			bufobj_wdrop(bp->b_bufobj);
  		bufobj_wref(&vp2->v_bufobj);
  	}
  	if (bp->b_bufobj != &vp2->v_bufobj)
  		bp->b_bufobj = &vp2->v_bufobj;
  	bp->b_vp = vp2;
  	bp->b_iooffset = dbtob(bp->b_blkno);
  	bstrategy(bp);
  	return;
  }
  
  static void
  swapdev_close(struct thread *td, struct swdevt *sp)
  {
  
  	VOP_CLOSE(sp->sw_vp, FREAD | FWRITE, td->td_ucred, td);
  	vrele(sp->sw_vp);
  }
  
  
  static int
  swaponvp(struct thread *td, struct vnode *vp, u_long nblks)
  {
  	struct swdevt *sp;
  	int error;
  
  	if (nblks == 0)
  		return (ENXIO);
  	mtx_lock(&sw_dev_mtx);
  	TAILQ_FOREACH(sp, &swtailq, sw_list) {
  		if (sp->sw_id == vp) {
  			mtx_unlock(&sw_dev_mtx);
  			return (EBUSY);
  		}
  	}
  	mtx_unlock(&sw_dev_mtx);
      
  	(void) vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
  #ifdef MAC
  	error = mac_system_check_swapon(td->td_ucred, vp);
  	if (error == 0)
  #endif
  		error = VOP_OPEN(vp, FREAD | FWRITE, td->td_ucred, td, NULL);
  	(void) VOP_UNLOCK(vp, 0);
  	if (error)
  		return (error);
  
  	swaponsomething(vp, vp, nblks, swapdev_strategy, swapdev_close,
  	    NODEV, 0);
  	return (0);
  }
  