xref: /src/sys/uvm/uvm_aobj.c

/*	$NetBSD: uvm_aobj.c,v 1.4 1998/02/07 11:08:08 mrg Exp $	*/

/* copyright here */
/*
 * from: Id: uvm_aobj.c,v 1.1.2.5 1998/02/06 05:14:38 chs Exp
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/malloc.h>

#include <vm/vm.h>
#include <vm/vm_page.h>
#include <vm/vm_kern.h>

#include <uvm/uvm.h>

/*
 * uvm_aobj.c: anonymous-memory backed uvm_object
 */

/*
 * an aobj manages anonymous-memory backed uvm_objects.   in addition
 * to keeping the list of resident pages, it also keeps a list of
 * allocated swap blocks.  depending on the size of the aobj this list
 * of allocated swap blocks is either stored in an array (small objects)
 * or in a hash table (large objects).
 */

/*
 * local structures
 */

/*
 * for hash tables, we break the address space of the aobj into blocks
 * of UAO_SWHASH_CLUSTER_SIZE pages.   we require the cluster size to
 * be a power of two.
 */

#define UAO_SWHASH_CLUSTER_SHIFT 4
#define UAO_SWHASH_CLUSTER_SIZE (1 << UAO_SWHASH_CLUSTER_SHIFT)

/* get the "tag" for this page index */
#define UAO_SWHASH_ELT_TAG(PAGEIDX) \
	((PAGEIDX) >> UAO_SWHASH_CLUSTER_SHIFT)

/* given an ELT and a page index, find the swap slot */
#define UAO_SWHASH_ELT_PAGESLOT(ELT, PAGEIDX) \
	((ELT)->slots[(PAGEIDX) & (UAO_SWHASH_CLUSTER_SIZE - 1)])

/* given an ELT, return its pageidx base */
#define UAO_SWHASH_ELT_PAGEIDX_BASE(ELT) \
	((ELT)->tag << UAO_SWHASH_CLUSTER_SHIFT)

/*
 * the swhash hash function
 */
#define UAO_SWHASH_HASH(AOBJ, PAGEIDX) \
	(&(AOBJ)->u_swhash[(((PAGEIDX) >> UAO_SWHASH_CLUSTER_SHIFT) \
			    & (AOBJ)->u_swhashmask)])

/*
 * the swhash threshhold determines if we will use an array or a
 * hash table to store the list of allocated swap blocks.
 */

#define UAO_SWHASH_THRESHOLD (UAO_SWHASH_CLUSTER_SIZE * 4)
#define UAO_USES_SWHASH(AOBJ) \
	((AOBJ)->u_pages > UAO_SWHASH_THRESHOLD)	/* use hash? */

/*
 * the number of buckets in a swhash, with an upper bound
 */
#define UAO_SWHASH_MAXBUCKETS 256
#define UAO_SWHASH_BUCKETS(AOBJ) \
	(min((AOBJ)->u_pages >> UAO_SWHASH_CLUSTER_SHIFT, \
	     UAO_SWHASH_MAXBUCKETS))


/*
 * uao_swhash_elt: when a hash table is being used, this structure defines
 * the format of an entry in the bucket list.
 */

struct uao_swhash_elt {
  LIST_ENTRY(uao_swhash_elt) list;	/* the hash list */
  vm_offset_t tag;			/* our 'tag' */
  int count;				/* our number of active slots */
  int slots[UAO_SWHASH_CLUSTER_SIZE];	/* the slots */
};

/*
 * uao_swhash: the swap hash table structure
 */

LIST_HEAD(uao_swhash, uao_swhash_elt);


/*
 * uvm_aobj: the actual anon-backed uvm_object
 *
 * => the uvm_object is at the top of the structure, this allows
 *   (struct uvm_device *) == (struct uvm_object *)
 * => only one of u_swslots and u_swhash is used in any given aobj
 */

struct uvm_aobj {
  struct uvm_object u_obj;	/* has: lock, pgops, memq, #pages, #refs */
  vm_size_t u_pages;		/* number of pages in entire object */
  int u_flags;			/* the flags (see uvm_aobj.h) */
  int *u_swslots;		/* array of offset->swapslot mappings */
  struct uao_swhash *u_swhash;	/* hashtable of offset->swapslot mappings */
  				/*  (u_swhash is an array of bucket heads) */
  u_long u_swhashmask;		/* mask for hashtable */
  LIST_ENTRY(uvm_aobj) u_list;	/* global list of aobjs */
};

/*
 * local functions
 */

static void			 uao_init __P((void));
static struct uao_swhash_elt	*uao_find_swhash_elt __P((struct uvm_aobj *,
							  int, boolean_t));
static int			 uao_find_swslot __P((struct uvm_aobj *,
						      vm_offset_t));
static boolean_t		 uao_flush __P((struct uvm_object *,
						vm_offset_t, vm_offset_t,
						int));
static void			 uao_free __P((struct uvm_aobj *));
static int			 uao_get __P((struct uvm_object *, vm_offset_t,
					      vm_page_t *, int *, int,
					      vm_prot_t, int, int));
static boolean_t		 uao_releasepg __P((struct vm_page *,
						    struct vm_page **));



/*
 * aobj_pager
 *
 * note that some functions (e.g. put) are handled elsewhere
 */

struct uvm_pagerops aobj_pager = {
  uao_init,		/* init */
  NULL,			/* attach */
  uao_reference,	/* reference */
  uao_detach,		/* detach */
  NULL,			/* fault */
  uao_flush,		/* flush */
  uao_get,		/* get */
  NULL,			/* asyncget */
  NULL,			/* put (done by pagedaemon) */
  NULL,			/* cluster */
  NULL,			/* mk_pcluster */
  uvm_shareprot,	/* shareprot */
  NULL,			/* aiodone */
  uao_releasepg		/* releasepg */
};

/*
 * uao_list: global list of active aobjs, locked by uao_list_lock
 */

static LIST_HEAD(aobjlist, uvm_aobj) uao_list;
#if NCPU > 1
static simple_lock_data_t uao_list_lock;
#endif


/*
 * functions
 */

/*
 * hash table/array related functions
 */

/*
 * uao_find_swhash_elt: find (or create) a hash table entry for a page
 * offset.
 *
 * => the object should be locked by the caller
 */

static struct uao_swhash_elt *uao_find_swhash_elt(aobj, pageidx, create)

struct uvm_aobj *aobj;
int pageidx;
boolean_t create;

{
  struct uao_swhash *swhash;
  struct uao_swhash_elt *elt;
  int page_tag;

  swhash = UAO_SWHASH_HASH(aobj, pageidx);	/* first hash to get bucket */
  page_tag = UAO_SWHASH_ELT_TAG(pageidx);	/* tag to search for */

  /*
   * now search the bucket for the requested tag
   */
  for (elt = swhash->lh_first; elt != NULL; elt = elt->list.le_next) {
    if (elt->tag == page_tag)
      return(elt);
  }

  /* fail now if we are not allowed to create a new entry in the bucket */
  if (!create)
    return NULL;


  /*
   * malloc a new entry for the bucket and init/insert it in
   */
  MALLOC(elt, struct uao_swhash_elt *, sizeof(*elt), M_UVMAOBJ, M_WAITOK);
  LIST_INSERT_HEAD(swhash, elt, list);
  elt->tag = page_tag;
  elt->count = 0;
  bzero(elt->slots, sizeof(elt->slots));

  return(elt);
}

/*
 * uao_find_swslot: find the swap slot number for an aobj/pageidx
 *
 * => object must be locked by caller
 */

__inline static int uao_find_swslot(aobj, pageidx)

struct uvm_aobj *aobj;
vm_offset_t pageidx;

{
  /*
   * if noswap flag is set, then we never return a slot
   */

  if (aobj->u_flags & UAO_FLAG_NOSWAP)
    return(0);

  /*
   * if hashing, look in hash table.
   */

  if (UAO_USES_SWHASH(aobj)) {
    struct uao_swhash_elt *elt = uao_find_swhash_elt(aobj, pageidx, FALSE);

    if (elt)
      return(UAO_SWHASH_ELT_PAGESLOT(elt, pageidx));
    else
      return(NULL);
  }

  /*
   * otherwise, look in the array
   */
  return(aobj->u_swslots[pageidx]);
}

/*
 * uao_set_swslot: set the swap slot for a page in an aobj.
 *
 * => setting a slot to zero frees the slot
 * => object must be locked by caller
 */

int uao_set_swslot(uobj, pageidx, slot)

struct uvm_object *uobj;
int pageidx, slot;

{
  struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
  int oldslot;
  UVMHIST_FUNC("uao_set_swslot"); UVMHIST_CALLED(pdhist);
  UVMHIST_LOG(pdhist, "aobj %p pageidx %d slot %d", aobj, pageidx, slot, 0);

  /*
   * if noswap flag is set, then we can't set a slot
   */

  if (aobj->u_flags & UAO_FLAG_NOSWAP) {

    if (slot == 0)
      return(0);		/* a clear is ok */

    /* but a set is not */
    printf("uao_set_swslot: uobj = %p\n", uobj);
    panic("uao_set_swslot: attempt to set a slot on a NOSWAP object");
  }

  /*
   * are we using a hash table?  if so, add it in the hash.
   */

  if (UAO_USES_SWHASH(aobj)) {
    struct uao_swhash_elt *elt = uao_find_swhash_elt(aobj, pageidx, TRUE);

    oldslot = UAO_SWHASH_ELT_PAGESLOT(elt, pageidx);
    UAO_SWHASH_ELT_PAGESLOT(elt, pageidx) = slot;

    /*
     * now adjust the elt's reference counter and free it if we've dropped
     * it to zero.
     */

    if (slot) {		/* an allocation? */

      if (oldslot == 0)
	elt->count++;

    } else {		/* freeing slot ... */

      if (oldslot)	/* to be safe (who would replace zero with zero?) */
	elt->count--;

      if (elt->count == 0) {
	LIST_REMOVE(elt, list);
	FREE(elt, M_UVMAOBJ);
      }
    }

  } else {

    /* we are using an array */
    oldslot = aobj->u_swslots[pageidx];
    aobj->u_swslots[pageidx] = slot;

  }

    return(oldslot);
}

/*
 * end of hash/array functions
 */

/*
 * uao_free: free all resources held by an aobj, and then free the aobj
 *
 * => the aobj should be dead
 */

static void
uao_free(aobj)
struct uvm_aobj *aobj;
{


  if (UAO_USES_SWHASH(aobj)) {
    int i, hashbuckets = aobj->u_swhashmask + 1;

    /*
     * free the swslots from each hash bucket,
     * then the hash bucket, and finally the hash table itself.
     */
    for (i = 0; i < hashbuckets; i++) {
      struct uao_swhash_elt *elt, *next;

      for (elt = aobj->u_swhash[i].lh_first; elt != NULL; elt = next) {
	int j;

	for (j = 0; j < UAO_SWHASH_CLUSTER_SIZE; j++)
	{
	    int slot = elt->slots[j];

	    if (slot)
	    {
		uvm_swap_free(slot, 1);
	    }
	}

	next = elt->list.le_next;
	FREE(elt, M_UVMAOBJ);
      }
    }
    FREE(aobj->u_swhash, M_UVMAOBJ);
  } else {
    int i;

    /*
     * free the array
     */

    for (i = 0; i < aobj->u_pages; i++)
    {
	int slot = aobj->u_swslots[i];

	if (slot)
	{
	    uvm_swap_free(slot, 1);
	}
    }

    FREE(aobj->u_swslots, M_UVMAOBJ);
  }

  /*
   * finally free the aobj itself
   */
  FREE(aobj, M_UVMAOBJ);
}


/*
 * pager functions
 */

/*
 * uao_create: create an aobj of the given size and return its uvm_object.
 *
 * => for normal use, flags are always zero
 * => for the kernel object, the flags are:
 *	UAO_FLAG_KERNOBJ - allocate the kernel object (can only happen once)
 *	UAO_FLAG_KERNSWAP - enable swapping of kernel object ("           ")
 */

struct uvm_object *uao_create(size, flags)

vm_size_t size;
int flags;

{
  static struct uvm_aobj kernel_object_store;	/* home of kernel_object */
  static int kobj_alloced = 0;			/* not allocated yet */
  int pages = round_page(size) / PAGE_SIZE;
  struct uvm_aobj *aobj;

  /*
   * malloc a new aobj unless we are asked for the kernel object
   */
  if (flags & UAO_FLAG_KERNOBJ) {		/* want kernel object? */
    if (kobj_alloced)
      panic("uao_create: kernel object already allocated");

    aobj = &kernel_object_store;
    aobj->u_pages = pages;
    aobj->u_flags = UAO_FLAG_NOSWAP;	/* no swap to start */
    aobj->u_obj.uo_refs = UVM_OBJ_KERN; /* we are special, we never die */
    kobj_alloced = UAO_FLAG_KERNOBJ;

  } else if (flags & UAO_FLAG_KERNSWAP) {

    aobj = &kernel_object_store;
    if (kobj_alloced != UAO_FLAG_KERNOBJ)
      panic("uao_create: asked to enable swap on kernel object");
    kobj_alloced = UAO_FLAG_KERNSWAP;

  } else {	/* normal object */

    MALLOC(aobj, struct uvm_aobj *, sizeof(*aobj), M_UVMAOBJ, M_WAITOK);
    aobj->u_pages = pages;
    aobj->u_flags = 0;		/* normal object */
    aobj->u_obj.uo_refs = 1;	/* start with 1 reference */

  }

  /*
   * allocate hash/array if necessary
   *
   * note: in the KERNSWAP case no need to worry about locking since
   * we are still booting we should be the only thread around.
   */

  if (flags == 0 || (flags & UAO_FLAG_KERNSWAP) != 0) {

    int mflags = (flags & UAO_FLAG_KERNSWAP) != 0 ? M_NOWAIT : M_WAITOK;

    /* allocate hash table or array depending on object size */
      if (UAO_USES_SWHASH(aobj)) {
      aobj->u_swhash = hashinit(UAO_SWHASH_BUCKETS(aobj), M_UVMAOBJ, mflags,
					&aobj->u_swhashmask);
      if (aobj->u_swhash == NULL)
	panic("uao_create: hashinit swhash failed");
    } else {
      MALLOC(aobj->u_swslots, int *, pages * sizeof(int), M_UVMAOBJ, mflags);
      if (aobj->u_swslots == NULL)
	panic("uao_create: malloc swslots failed");
      bzero(aobj->u_swslots, pages * sizeof(int));
    }

    if (flags) {
      aobj->u_flags &= ~UAO_FLAG_NOSWAP;	/* clear noswap */
      return(&aobj->u_obj);
      /* done! */
    }
  }

  /*
   * init aobj fields
   */
  simple_lock_init(&aobj->u_obj.vmobjlock);
  aobj->u_obj.pgops = &aobj_pager;
  TAILQ_INIT(&aobj->u_obj.memq);
  aobj->u_obj.uo_npages = 0;

  /*
   * now that aobj is ready, add it to the global list
   * XXXCHS: uao_init hasn't been called'd in the KERNOBJ case, do we really
   * need the kernel object on this list anyway?
   */
  simple_lock(&uao_list_lock);
  LIST_INSERT_HEAD(&uao_list, aobj, u_list);
  simple_unlock(&uao_list_lock);

  /*
   * done!
   */
  return(&aobj->u_obj);
}



/*
 * uao_init: set up aobj pager subsystem
 *
 * => called at boot time from uvm_pager_init()
 */

static void uao_init()

{
  LIST_INIT(&uao_list);
  simple_lock_init(&uao_list_lock);
}

/*
 * uao_reference: add a ref to an aobj
 *
 * => aobj must be unlocked (we will lock it)
 */

void uao_reference(uobj)

struct uvm_object *uobj;

{
  UVMHIST_FUNC("uao_reference"); UVMHIST_CALLED(maphist);

  /*
   * kernel_object already has plenty of references, leave it alone.
   */

  if (uobj->uo_refs == UVM_OBJ_KERN) {
    return;
  }

  simple_lock(&uobj->vmobjlock);
  uobj->uo_refs++;		/* bump! */
  UVMHIST_LOG(maphist, "<- done (uobj=0x%x, ref = %d)",
	uobj, uobj->uo_refs,0,0);
  simple_unlock(&uobj->vmobjlock);
}

/*
 * uao_detach: drop a reference to an aobj
 *
 * => aobj must be unlocked, we will lock it
 */

void uao_detach(uobj)

struct uvm_object *uobj;

{
  struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
  struct vm_page *pg;
  boolean_t busybody;
  UVMHIST_FUNC("uao_detach"); UVMHIST_CALLED(maphist);

  /*
   * detaching from kernel_object is a noop.
   */

  if (uobj->uo_refs == UVM_OBJ_KERN) {
    return;
  }

  simple_lock(&uobj->vmobjlock);

  UVMHIST_LOG(maphist,"  (uobj=0x%x)  ref=%d", uobj,uobj->uo_refs,0,0);
  uobj->uo_refs--;				/* drop ref! */
  if (uobj->uo_refs) {				/* still more refs? */
    simple_unlock(&uobj->vmobjlock);
    UVMHIST_LOG(maphist, "<- done (rc>0)", 0,0,0,0);
    return;
  }

  /*
   * remove the aobj from the global list.
   */
  simple_lock(&uao_list_lock);
  LIST_REMOVE(aobj, u_list);
  simple_unlock(&uao_list_lock);

  /*
   * free all the pages that aren't PG_BUSY, mark for release any that are.
   */

  busybody = FALSE;
  for (pg = uobj->memq.tqh_first ; pg != NULL ; pg = pg->listq.tqe_next) {
    int swslot;

    if (pg->flags & PG_BUSY) {
      pg->flags |= PG_RELEASED;
      busybody = TRUE;
      continue;
    }


    /* zap the mappings, free the swap slot, free the page */
    pmap_page_protect(PMAP_PGARG(pg), VM_PROT_NONE);

    swslot = uao_set_swslot(&aobj->u_obj, pg->offset / PAGE_SIZE, 0);
    if (swslot)	{
      uvm_swap_free(swslot, 1);
    }

    uvm_lock_pageq();
    uvm_pagefree(pg);
    uvm_unlock_pageq();
  }

  /*
   * if we found any busy pages, we're done for now.
   * mark the aobj for death, releasepg will finish up for us.
   */
  if (busybody) {
    aobj->u_flags |= UAO_FLAG_KILLME;
    simple_unlock(&aobj->u_obj.vmobjlock);
    return;
  }

  /*
   * finally, free the rest.
   */
  uao_free(aobj);
}



/*
 * uao_flush: uh, yea, sure it's flushed.  really!
 */
boolean_t uao_flush(uobj, start, end, flags)

struct uvm_object *uobj;
vm_offset_t start, end;
int flags;

{
  /*
   * anonymous memory doesn't "flush"
   */
  /*
   * XXX
   * deal with PGO_DEACTIVATE (for madvise(MADV_SEQUENTIAL))
   * and PGO_FREE (for msync(MSINVALIDATE))
   */
  return TRUE;
}

/*
 * uao_get: fetch me a page
 *
 * we have three cases:
 * 1: page is resident     -> just return the page.
 * 2: page is zero-fill    -> allocate a new page and zero it.
 * 3: page is swapped out  -> fetch the page from swap.
 *
 * cases 1 and 2 can be handled with PGO_LOCKED, case 3 cannot.
 * so, if the "center" page hits case 3 (or any page, with PGO_ALLPAGES),
 * then we will need to return VM_PAGER_UNLOCK.
 *
 * => prefer map unlocked (not required)
 * => object must be locked!  we will _unlock_ it before starting any I/O.
 * => flags: PGO_ALLPAGES: get all of the pages
 *           PGO_LOCKED: fault data structures are locked
 * => NOTE: offset is the offset of pps[0], _NOT_ pps[centeridx]
 * => NOTE: caller must check for released pages!!
 */

static int uao_get(uobj, offset, pps, npagesp, centeridx, access_type,
		   advice, flags)

struct uvm_object *uobj;
vm_offset_t offset;
struct vm_page **pps;
int *npagesp;
int centeridx, advice, flags;
vm_prot_t access_type;

{
  struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
  vm_offset_t current_offset;
  vm_page_t ptmp;
  int lcv, gotpages, maxpages, swslot, rv;
  boolean_t done;
  UVMHIST_FUNC("uao_get"); UVMHIST_CALLED(pdhist);

  UVMHIST_LOG(pdhist, "aobj=%p offset=%d, flags=%d", aobj, offset, flags,0);

  /*
   * get number of pages
   */

  maxpages = *npagesp;

  /*
   * step 1: handled the case where fault data structures are locked.
   */

  if (flags & PGO_LOCKED) {

    /*
     * step 1a: get pages that are already resident.   only do this
     * if the data structures are locked (i.e. the first time through).
     */

    done = TRUE;	/* be optimistic */
    gotpages = 0;	/* # of pages we got so far */

    for (lcv = 0, current_offset = offset ;
	 lcv < maxpages ; lcv++, current_offset += PAGE_SIZE) {

      /* do we care about this page?  if not, skip it */
      if (pps[lcv] == PGO_DONTCARE)
	continue;

      ptmp = uvm_pagelookup(uobj, current_offset);

      /*
       * if page is new, attempt to allocate the page, then zero-fill it.
       */
      if (ptmp == NULL &&
	  uao_find_swslot(aobj, current_offset / PAGE_SIZE) == 0) {

	ptmp = uvm_pagealloc(uobj, current_offset, NULL);
	if (ptmp) {
	  ptmp->flags &= ~(PG_BUSY|PG_FAKE);	/* new page */
	  ptmp->pqflags |= PQ_AOBJ;
	  UVM_PAGE_OWN(ptmp, NULL);
	  uvm_pagezero(ptmp);
	}
      }

      /* to be useful must get a non-busy, non-released page */
      if (ptmp == NULL || (ptmp->flags & (PG_BUSY|PG_RELEASED)) != 0) {
	if (lcv == centeridx || (flags & PGO_ALLPAGES) != 0)
	  done = FALSE;		/* need to do a wait or I/O! */
	continue;
      }

      /* useful page: busy/lock it and plug it in our result array */
      ptmp->flags |= PG_BUSY;		/* caller must un-busy this page */
      UVM_PAGE_OWN(ptmp, "uao_get1");
      pps[lcv] = ptmp;
      gotpages++;

    }	/* "for" lcv loop */

    /*
     * step 1b: now we've either done everything needed or we to unlock
     * and do some waiting or I/O.
     */

    UVMHIST_LOG(pdhist, "<- done (done=%d)", done, 0,0,0);

    *npagesp = gotpages;
    if (done)
      return(VM_PAGER_OK);		/* bingo! */
    else
      return(VM_PAGER_UNLOCK);		/* EEK!   Need to unlock and I/O */
  }

  /*
   * step 2: get non-resident or busy pages.
   * object is locked.   data structures are unlocked.
   */

  for (lcv = 0, current_offset = offset ;
       lcv < maxpages ;
       lcv++, current_offset += PAGE_SIZE) {

    /* skip over pages we've already gotten or don't want */
    /* skip over pages we don't _have_ to get */
    if (pps[lcv] != NULL ||
	(lcv != centeridx && (flags & PGO_ALLPAGES) == 0))
      continue;

    /*
     * we have yet to locate the current page (pps[lcv]).   we first
     * look for a page that is already at the current offset.   if we
     * find a page, we check to see if it is busy or released.  if that
     * is the case, then we sleep on the page until it is no longer busy
     * or released and repeat the lookup.    if the page we found is
     * neither busy nor released, then we busy it (so we own it) and
     * plug it into pps[lcv].   this 'break's the following while loop
     * and indicates we are ready to move on to the next page in the
     * "lcv" loop above.
     *
     * if we exit the while loop with pps[lcv] still set to NULL, then
     * it means that we allocated a new busy/fake/clean page ptmp in the
     * object and we need to do I/O to fill in the data.
     */

    while (pps[lcv] == NULL) {		/* top of "pps" while loop */

      /* look for a resident page */
      ptmp = uvm_pagelookup(uobj, current_offset);

      /* not resident?   allocate one now (if we can) */
      if (ptmp == NULL) {

	ptmp = uvm_pagealloc(uobj, current_offset, NULL);	/* alloc */

	/* out of RAM? */
	if (ptmp == NULL) {
	  simple_unlock(&uobj->vmobjlock);
	  UVMHIST_LOG(pdhist, "sleeping, ptmp == NULL\n",0,0,0,0);
	  uvm_wait("uao_getpage");
	  simple_lock(&uobj->vmobjlock);
	  continue;		/* goto top of pps while loop */
	}

	/* safe with PQ's unlocked: because we just alloc'd the page */
	ptmp->pqflags |= PQ_AOBJ;

	/*
	 * got new page ready for I/O.  break pps while loop.  pps[lcv] is
	 * still NULL.
	 */
	break;
      }

      /* page is there, see if we need to wait on it */
      if ((ptmp->flags & (PG_BUSY|PG_RELEASED)) != 0) {
	ptmp->flags |= PG_WANTED;
	UVMHIST_LOG(pdhist, "sleeping, ptmp->flags 0x%x\n",ptmp->flags,0,0,0);
	UVM_UNLOCK_AND_WAIT(ptmp,&uobj->vmobjlock,0,"uao_get",0);
	simple_lock(&uobj->vmobjlock);
	continue;		/* goto top of pps while loop */
      }

      /*
       * if we get here then the page has become resident and unbusy
       * between steps 1 and 2.  we busy it now (so we own it) and set
       * pps[lcv] (so that we exit the while loop).
       */
      ptmp->flags |= PG_BUSY;	/* we own it, caller must un-busy */
      UVM_PAGE_OWN(ptmp, "uao_get2");
      pps[lcv] = ptmp;
    }

    /*
     * if we own the valid page at the correct offset, pps[lcv] will
     * point to it.   nothing more to do except go to the next page.
     */

    if (pps[lcv])
      continue;			/* next lcv */

    /*
     * we have a "fake/busy/clean" page that we just allocated.
     * do the needed "i/o", either reading from swap or zeroing.
     */

    swslot = uao_find_swslot(aobj, current_offset / PAGE_SIZE);

    /*
     * just zero the page if there's nothing in swap.
     */
    if (swslot == 0)
    {
	/*
	 * page hasn't existed before, just zero it.
	 */
	uvm_pagezero(ptmp);
    }
    else
    {
	UVMHIST_LOG(pdhist, "pagein from swslot %d", swslot, 0,0,0);

	/*
	 * page in the swapped-out page.
	 * unlock object for i/o, relock when done.
	 */
	simple_unlock(&uobj->vmobjlock);
	rv = uvm_swap_get(ptmp, swslot, PGO_SYNCIO);
	simple_lock(&uobj->vmobjlock);

	/*
	 * I/O done.  check for errors.
	 */
	if (rv != VM_PAGER_OK)
	{
	    UVMHIST_LOG(pdhist, "<- done (error=%d)",rv,0,0,0);
	    if (ptmp->flags & PG_WANTED)
		thread_wakeup(ptmp);		/* object lock still held */
	    ptmp->flags &= ~(PG_WANTED|PG_BUSY);
	    UVM_PAGE_OWN(ptmp, NULL);
	    uvm_lock_pageq();
	    uvm_pagefree(ptmp);
	    uvm_unlock_pageq();
	    simple_unlock(&uobj->vmobjlock);
	    return rv;
	}
    }

    /*
     * we got the page!   clear the fake flag (indicates valid data now
     * in page) and plug into our result array.   note that page is still
     * busy.
     *
     * it is the callers job to:
     * => check if the page is released
     * => unbusy the page
     * => activate the page
     */

    ptmp->flags &= ~PG_FAKE;			/* data is valid ... */
    pmap_clear_modify(PMAP_PGARG(ptmp));	/* ... and clean */
    pps[lcv] = ptmp;

  }	/* lcv loop */

  /*
   * finally, unlock object and return.
   */

  simple_unlock(&uobj->vmobjlock);
  UVMHIST_LOG(pdhist, "<- done (OK)",0,0,0,0);
  return(VM_PAGER_OK);
}

/*
 * uao_releasepg: handle released page in an aobj
 *
 * => "pg" is a PG_BUSY [caller owns it], PG_RELEASED page that we need
 *      to dispose of.
 * => caller must handle PG_WANTED case
 * => called with page's object locked, pageq's unlocked
 * => returns TRUE if page's object is still alive, FALSE if we
 *      killed the page's object.    if we return TRUE, then we
 *      return with the object locked.
 * => if (nextpgp != NULL) => we return pageq.tqe_next here, and return
 *                              with the page queues locked [for pagedaemon]
 * => if (nextpgp == NULL) => we return with page queues unlocked [normal case]
 * => we kill the aobj if it is not referenced and we are suppose to
 *      kill it ("KILLME").
 */

static boolean_t uao_releasepg(pg, nextpgp)

struct vm_page *pg;
struct vm_page **nextpgp;	/* OUT */

{
  struct uvm_aobj *aobj = (struct uvm_aobj *) pg->uobject;
  int slot;

#ifdef DIAGNOSTIC
  if ((pg->flags & PG_RELEASED) == 0)
    panic("uao_releasepg: page not released!");
#endif

  /*
   * dispose of the page [caller handles PG_WANTED] and swap slot.
   */
  pmap_page_protect(PMAP_PGARG(pg), VM_PROT_NONE);
  slot = uao_set_swslot(&aobj->u_obj, pg->offset / PAGE_SIZE, 0);
  if (slot)
    uvm_swap_free(slot, 1);
  uvm_lock_pageq();
  if (nextpgp)
    *nextpgp = pg->pageq.tqe_next;	/* next page for daemon */
  uvm_pagefree(pg);
  if (!nextpgp)
    uvm_unlock_pageq();			/* keep locked for daemon */

  /*
   * if we're not killing the object, we're done.
   */
  if ((aobj->u_flags & UAO_FLAG_KILLME) == 0)
    return TRUE;

#ifdef DIAGNOSTIC
  if (aobj->u_obj.uo_refs)
    panic("uvm_km_releasepg: kill flag set on referenced object!");
#endif

  /*
   * if there are still pages in the object, we're done for now.
   */
  if (aobj->u_obj.uo_npages != 0)
    return TRUE;

#ifdef DIAGNOSTIC
  if (aobj->u_obj.memq.tqh_first)
    panic("uvn_releasepg: pages in object with npages == 0");
#endif

  /*
   * finally, free the rest.
   */
  uao_free(aobj);

  return FALSE;
}