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

     /*      $NetBSD: uvm_page.c,v 1.97.2.2 2004/09/11 11:00:34 he Exp $     */
     
     /*
      * Copyright (c) 1997 Charles D. Cranor and Washington University.
      * Copyright (c) 1991, 1993, The Regents of the University of California.
      *
      * All rights reserved.
      *
      * This code is derived from software contributed to Berkeley by
     * The Mach Operating System project at Carnegie-Mellon University.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by Charles D. Cranor,
     *      Washington University, the University of California, Berkeley and
     *      its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)vm_page.c   8.3 (Berkeley) 3/21/94
     * from: Id: uvm_page.c,v 1.1.2.18 1998/02/06 05:24:42 chs Exp
     *
     *
     * Copyright (c) 1987, 1990 Carnegie-Mellon University.
     * All rights reserved.
     *
     * Permission to use, copy, modify and distribute this software and
     * its documentation is hereby granted, provided that both the copyright
     * notice and this permission notice appear in all copies of the
     * software, derivative works or modified versions, and any portions
     * thereof, and that both notices appear in supporting documentation.
     *
     * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
     * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
     * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
     *
     * Carnegie Mellon requests users of this software to return to
     *
     *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
     *  School of Computer Science
     *  Carnegie Mellon University
     *  Pittsburgh PA 15213-3890
     *
     * any improvements or extensions that they make and grant Carnegie the
     * rights to redistribute these changes.
     */
    
    /*
     * uvm_page.c: page ops.
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: uvm_page.c,v 1.97.2.2 2004/09/11 11:00:34 he Exp $");
    
    #include "opt_uvmhist.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/malloc.h>
    #include <sys/sched.h>
    #include <sys/kernel.h>
    #include <sys/vnode.h>
    #include <sys/proc.h>
    
    #define UVM_PAGE                /* pull in uvm_page.h functions */
    #include <uvm/uvm.h>
    
    /*
     * global vars... XXXCDC: move to uvm. structure.
     */
    
    /*
     * physical memory config is stored in vm_physmem.
     */
    
    struct vm_physseg vm_physmem[VM_PHYSSEG_MAX];   /* XXXCDC: uvm.physmem */
    int vm_nphysseg = 0;                            /* XXXCDC: uvm.nphysseg */
    
   /*
    * Some supported CPUs in a given architecture don't support all
    * of the things necessary to do idle page zero'ing efficiently.
    * We therefore provide a way to disable it from machdep code here.
    */
   /*
    * XXX disabled until we can find a way to do this without causing
    * problems for either CPU caches or DMA latency.
    */
   boolean_t vm_page_zero_enable = FALSE;
   
   /*
    * local variables
    */
   
   /*
    * these variables record the values returned by vm_page_bootstrap,
    * for debugging purposes.  The implementation of uvm_pageboot_alloc
    * and pmap_startup here also uses them internally.
    */
   
   static vaddr_t      virtual_space_start;
   static vaddr_t      virtual_space_end;
   
   /*
    * we use a hash table with only one bucket during bootup.  we will
    * later rehash (resize) the hash table once the allocator is ready.
    * we static allocate the one bootstrap bucket below...
    */
   
   static struct pglist uvm_bootbucket;
   
   /*
    * we allocate an initial number of page colors in uvm_page_init(),
    * and remember them.  We may re-color pages as cache sizes are
    * discovered during the autoconfiguration phase.  But we can never
    * free the initial set of buckets, since they are allocated using
    * uvm_pageboot_alloc().
    */
   
   static boolean_t have_recolored_pages /* = FALSE */;
   
   MALLOC_DEFINE(M_VMPAGE, "VM page", "VM page");
   
   #ifdef DEBUG
   vaddr_t uvm_zerocheckkva;
   #endif /* DEBUG */
   
   /*
    * local prototypes
    */
   
   static void uvm_pageinsert(struct vm_page *);
   static void uvm_pageinsert_after(struct vm_page *, struct vm_page *);
   static void uvm_pageremove(struct vm_page *);
   
   /*
    * inline functions
    */
   
   /*
    * uvm_pageinsert: insert a page in the object and the hash table
    * uvm_pageinsert_after: insert a page into the specified place in listq
    *
    * => caller must lock object
    * => caller must lock page queues
    * => call should have already set pg's object and offset pointers
    *    and bumped the version counter
    */
   
   __inline static void
   uvm_pageinsert_after(pg, where)
           struct vm_page *pg;
           struct vm_page *where;
   {
           struct pglist *buck;
           struct uvm_object *uobj = pg->uobject;
   
           KASSERT((pg->flags & PG_TABLED) == 0);
           KASSERT(where == NULL || (where->flags & PG_TABLED));
           KASSERT(where == NULL || (where->uobject == uobj));
           buck = &uvm.page_hash[uvm_pagehash(uobj, pg->offset)];
           simple_lock(&uvm.hashlock);
           TAILQ_INSERT_TAIL(buck, pg, hashq);
           simple_unlock(&uvm.hashlock);
   
           if (UVM_OBJ_IS_VNODE(uobj)) {
                   if (uobj->uo_npages == 0) {
                           struct vnode *vp = (struct vnode *)uobj;
   
                           vholdl(vp);
                   }
                   if (UVM_OBJ_IS_VTEXT(uobj)) {
                           uvmexp.execpages++;
                   } else {
                           uvmexp.filepages++;
                   }
           } else if (UVM_OBJ_IS_AOBJ(uobj)) {
                   uvmexp.anonpages++;
           }
   
           if (where)
                   TAILQ_INSERT_AFTER(&uobj->memq, where, pg, listq);
           else
                   TAILQ_INSERT_TAIL(&uobj->memq, pg, listq);
           pg->flags |= PG_TABLED;
           uobj->uo_npages++;
   }
   
   __inline static void
   uvm_pageinsert(pg)
           struct vm_page *pg;
   {
   
           uvm_pageinsert_after(pg, NULL);
   }
   
   /*
    * uvm_page_remove: remove page from object and hash
    *
    * => caller must lock object
    * => caller must lock page queues
    */
   
   static __inline void
   uvm_pageremove(pg)
           struct vm_page *pg;
   {
           struct pglist *buck;
           struct uvm_object *uobj = pg->uobject;
   
           KASSERT(pg->flags & PG_TABLED);
           buck = &uvm.page_hash[uvm_pagehash(uobj, pg->offset)];
           simple_lock(&uvm.hashlock);
           TAILQ_REMOVE(buck, pg, hashq);
           simple_unlock(&uvm.hashlock);
   
           if (UVM_OBJ_IS_VNODE(uobj)) {
                   if (uobj->uo_npages == 1) {
                           struct vnode *vp = (struct vnode *)uobj;
   
                           holdrelel(vp);
                   }
                   if (UVM_OBJ_IS_VTEXT(uobj)) {
                           uvmexp.execpages--;
                   } else {
                           uvmexp.filepages--;
                   }
           } else if (UVM_OBJ_IS_AOBJ(uobj)) {
                   uvmexp.anonpages--;
           }
   
           /* object should be locked */
           uobj->uo_npages--;
           TAILQ_REMOVE(&uobj->memq, pg, listq);
           pg->flags &= ~PG_TABLED;
           pg->uobject = NULL;
   }
   
   static void
   uvm_page_init_buckets(struct pgfreelist *pgfl)
   {
           int color, i;
   
           for (color = 0; color < uvmexp.ncolors; color++) {
                   for (i = 0; i < PGFL_NQUEUES; i++) {
                           TAILQ_INIT(&pgfl->pgfl_buckets[color].pgfl_queues[i]);
                   }
           }
   }
   
   /*
    * uvm_page_init: init the page system.   called from uvm_init().
    *
    * => we return the range of kernel virtual memory in kvm_startp/kvm_endp
    */
   
   void
   uvm_page_init(kvm_startp, kvm_endp)
           vaddr_t *kvm_startp, *kvm_endp;
   {
           vsize_t freepages, pagecount, bucketcount, n;
           struct pgflbucket *bucketarray;
           struct vm_page *pagearray;
           int lcv;
           u_int i;
           paddr_t paddr;
   
           /*
            * init the page queues and page queue locks, except the free
            * list; we allocate that later (with the initial vm_page
            * structures).
            */
   
           TAILQ_INIT(&uvm.page_active);
           TAILQ_INIT(&uvm.page_inactive);
           simple_lock_init(&uvm.pageqlock);
           simple_lock_init(&uvm.fpageqlock);
   
           /*
            * init the <obj,offset> => <page> hash table.  for now
            * we just have one bucket (the bootstrap bucket).  later on we
            * will allocate new buckets as we dynamically resize the hash table.
            */
   
           uvm.page_nhash = 1;                     /* 1 bucket */
           uvm.page_hashmask = 0;                  /* mask for hash function */
           uvm.page_hash = &uvm_bootbucket;        /* install bootstrap bucket */
           TAILQ_INIT(uvm.page_hash);              /* init hash table */
           simple_lock_init(&uvm.hashlock);        /* init hash table lock */
   
           /*
            * allocate vm_page structures.
            */
   
           /*
            * sanity check:
            * before calling this function the MD code is expected to register
            * some free RAM with the uvm_page_physload() function.   our job
            * now is to allocate vm_page structures for this memory.
            */
   
           if (vm_nphysseg == 0)
                   panic("uvm_page_bootstrap: no memory pre-allocated");
   
           /*
            * first calculate the number of free pages...
            *
            * note that we use start/end rather than avail_start/avail_end.
            * this allows us to allocate extra vm_page structures in case we
            * want to return some memory to the pool after booting.
            */
   
           freepages = 0;
           for (lcv = 0 ; lcv < vm_nphysseg ; lcv++)
                   freepages += (vm_physmem[lcv].end - vm_physmem[lcv].start);
   
           /*
            * Let MD code initialize the number of colors, or default
            * to 1 color if MD code doesn't care.
            */
           if (uvmexp.ncolors == 0)
                   uvmexp.ncolors = 1;
           uvmexp.colormask = uvmexp.ncolors - 1;
   
           /*
            * we now know we have (PAGE_SIZE * freepages) bytes of memory we can
            * use.   for each page of memory we use we need a vm_page structure.
            * thus, the total number of pages we can use is the total size of
            * the memory divided by the PAGE_SIZE plus the size of the vm_page
            * structure.   we add one to freepages as a fudge factor to avoid
            * truncation errors (since we can only allocate in terms of whole
            * pages).
            */
   
           bucketcount = uvmexp.ncolors * VM_NFREELIST;
           pagecount = ((freepages + 1) << PAGE_SHIFT) /
               (PAGE_SIZE + sizeof(struct vm_page));
   
           bucketarray = (void *)uvm_pageboot_alloc((bucketcount *
               sizeof(struct pgflbucket)) + (pagecount *
               sizeof(struct vm_page)));
           pagearray = (struct vm_page *)(bucketarray + bucketcount);
   
           for (lcv = 0; lcv < VM_NFREELIST; lcv++) {
                   uvm.page_free[lcv].pgfl_buckets =
                       (bucketarray + (lcv * uvmexp.ncolors));
                   uvm_page_init_buckets(&uvm.page_free[lcv]);
           }
           memset(pagearray, 0, pagecount * sizeof(struct vm_page));
   
           /*
            * init the vm_page structures and put them in the correct place.
            */
   
           for (lcv = 0 ; lcv < vm_nphysseg ; lcv++) {
                   n = vm_physmem[lcv].end - vm_physmem[lcv].start;
   
                   /* set up page array pointers */
                   vm_physmem[lcv].pgs = pagearray;
                   pagearray += n;
                   pagecount -= n;
                   vm_physmem[lcv].lastpg = vm_physmem[lcv].pgs + (n - 1);
   
                   /* init and free vm_pages (we've already zeroed them) */
                   paddr = ptoa(vm_physmem[lcv].start);
                   for (i = 0 ; i < n ; i++, paddr += PAGE_SIZE) {
                           vm_physmem[lcv].pgs[i].phys_addr = paddr;
   #ifdef __HAVE_VM_PAGE_MD
                           VM_MDPAGE_INIT(&vm_physmem[lcv].pgs[i]);
   #endif
                           if (atop(paddr) >= vm_physmem[lcv].avail_start &&
                               atop(paddr) <= vm_physmem[lcv].avail_end) {
                                   uvmexp.npages++;
                                   /* add page to free pool */
                                   uvm_pagefree(&vm_physmem[lcv].pgs[i]);
                           }
                   }
           }
   
           /*
            * pass up the values of virtual_space_start and
            * virtual_space_end (obtained by uvm_pageboot_alloc) to the upper
            * layers of the VM.
            */
   
           *kvm_startp = round_page(virtual_space_start);
           *kvm_endp = trunc_page(virtual_space_end);
   #ifdef DEBUG
           /*
            * steal kva for uvm_pagezerocheck().
            */
           uvm_zerocheckkva = *kvm_startp;
           *kvm_startp += PAGE_SIZE;
   #endif /* DEBUG */
   
           /*
            * init locks for kernel threads
            */
   
           simple_lock_init(&uvm.pagedaemon_lock);
           simple_lock_init(&uvm.aiodoned_lock);
   
           /*
            * init various thresholds.
            */
   
           uvmexp.reserve_pagedaemon = 1;
           uvmexp.reserve_kernel = 5;
           uvmexp.anonminpct = 10;
           uvmexp.fileminpct = 10;
           uvmexp.execminpct = 5;
           uvmexp.anonmaxpct = 80;
           uvmexp.filemaxpct = 50;
           uvmexp.execmaxpct = 30;
           uvmexp.anonmin = uvmexp.anonminpct * 256 / 100;
           uvmexp.filemin = uvmexp.fileminpct * 256 / 100;
           uvmexp.execmin = uvmexp.execminpct * 256 / 100;
           uvmexp.anonmax = uvmexp.anonmaxpct * 256 / 100;
           uvmexp.filemax = uvmexp.filemaxpct * 256 / 100;
           uvmexp.execmax = uvmexp.execmaxpct * 256 / 100;
   
           /*
            * determine if we should zero pages in the idle loop.
            */
   
           uvm.page_idle_zero = vm_page_zero_enable;
   
           /*
            * done!
            */
   
           uvm.page_init_done = TRUE;
   }
   
   /*
    * uvm_setpagesize: set the page size
    *
    * => sets page_shift and page_mask from uvmexp.pagesize.
    */
   
   void
   uvm_setpagesize()
   {
   
           /*
            * If uvmexp.pagesize is 0 at this point, we expect PAGE_SIZE
            * to be a constant (indicated by being a non-zero value).
            */
           if (uvmexp.pagesize == 0) {
                   if (PAGE_SIZE == 0)
                           panic("uvm_setpagesize: uvmexp.pagesize not set");
                   uvmexp.pagesize = PAGE_SIZE;
           }
           uvmexp.pagemask = uvmexp.pagesize - 1;
           if ((uvmexp.pagemask & uvmexp.pagesize) != 0)
                   panic("uvm_setpagesize: page size not a power of two");
           for (uvmexp.pageshift = 0; ; uvmexp.pageshift++)
                   if ((1 << uvmexp.pageshift) == uvmexp.pagesize)
                           break;
   }
   
   /*
    * uvm_pageboot_alloc: steal memory from physmem for bootstrapping
    */
   
   vaddr_t
   uvm_pageboot_alloc(size)
           vsize_t size;
   {
           static boolean_t initialized = FALSE;
           vaddr_t addr;
   #if !defined(PMAP_STEAL_MEMORY)
           vaddr_t vaddr;
           paddr_t paddr;
   #endif
   
           /*
            * on first call to this function, initialize ourselves.
            */
           if (initialized == FALSE) {
                   pmap_virtual_space(&virtual_space_start, &virtual_space_end);
   
                   /* round it the way we like it */
                   virtual_space_start = round_page(virtual_space_start);
                   virtual_space_end = trunc_page(virtual_space_end);
   
                   initialized = TRUE;
           }
   
           /* round to page size */
           size = round_page(size);
   
   #if defined(PMAP_STEAL_MEMORY)
   
           /*
            * defer bootstrap allocation to MD code (it may want to allocate
            * from a direct-mapped segment).  pmap_steal_memory should adjust
            * virtual_space_start/virtual_space_end if necessary.
            */
   
           addr = pmap_steal_memory(size, &virtual_space_start,
               &virtual_space_end);
   
           return(addr);
   
   #else /* !PMAP_STEAL_MEMORY */
   
           /*
            * allocate virtual memory for this request
            */
           if (virtual_space_start == virtual_space_end ||
               (virtual_space_end - virtual_space_start) < size)
                   panic("uvm_pageboot_alloc: out of virtual space");
   
           addr = virtual_space_start;
   
   #ifdef PMAP_GROWKERNEL
           /*
            * If the kernel pmap can't map the requested space,
            * then allocate more resources for it.
            */
           if (uvm_maxkaddr < (addr + size)) {
                   uvm_maxkaddr = pmap_growkernel(addr + size);
                   if (uvm_maxkaddr < (addr + size))
                           panic("uvm_pageboot_alloc: pmap_growkernel() failed");
           }
   #endif
   
           virtual_space_start += size;
   
           /*
            * allocate and mapin physical pages to back new virtual pages
            */
   
           for (vaddr = round_page(addr) ; vaddr < addr + size ;
               vaddr += PAGE_SIZE) {
   
                   if (!uvm_page_physget(&paddr))
                           panic("uvm_pageboot_alloc: out of memory");
   
                   /*
                    * Note this memory is no longer managed, so using
                    * pmap_kenter is safe.
                    */
                   pmap_kenter_pa(vaddr, paddr, VM_PROT_READ|VM_PROT_WRITE);
           }
           pmap_update(pmap_kernel());
           return(addr);
   #endif  /* PMAP_STEAL_MEMORY */
   }
   
   #if !defined(PMAP_STEAL_MEMORY)
   /*
    * uvm_page_physget: "steal" one page from the vm_physmem structure.
    *
    * => attempt to allocate it off the end of a segment in which the "avail"
    *    values match the start/end values.   if we can't do that, then we
    *    will advance both values (making them equal, and removing some
    *    vm_page structures from the non-avail area).
    * => return false if out of memory.
    */
   
   /* subroutine: try to allocate from memory chunks on the specified freelist */
   static boolean_t uvm_page_physget_freelist(paddr_t *, int);
   
   static boolean_t
   uvm_page_physget_freelist(paddrp, freelist)
           paddr_t *paddrp;
           int freelist;
   {
           int lcv, x;
   
           /* pass 1: try allocating from a matching end */
   #if (VM_PHYSSEG_STRAT == VM_PSTRAT_BIGFIRST)
           for (lcv = vm_nphysseg - 1 ; lcv >= 0 ; lcv--)
   #else
           for (lcv = 0 ; lcv < vm_nphysseg ; lcv++)
   #endif
           {
   
                   if (uvm.page_init_done == TRUE)
                           panic("uvm_page_physget: called _after_ bootstrap");
   
                   if (vm_physmem[lcv].free_list != freelist)
                           continue;
   
                   /* try from front */
                   if (vm_physmem[lcv].avail_start == vm_physmem[lcv].start &&
                       vm_physmem[lcv].avail_start < vm_physmem[lcv].avail_end) {
                           *paddrp = ptoa(vm_physmem[lcv].avail_start);
                           vm_physmem[lcv].avail_start++;
                           vm_physmem[lcv].start++;
                           /* nothing left?   nuke it */
                           if (vm_physmem[lcv].avail_start ==
                               vm_physmem[lcv].end) {
                                   if (vm_nphysseg == 1)
                                       panic("uvm_page_physget: out of memory!");
                                   vm_nphysseg--;
                                   for (x = lcv ; x < vm_nphysseg ; x++)
                                           /* structure copy */
                                           vm_physmem[x] = vm_physmem[x+1];
                           }
                           return (TRUE);
                   }
   
                   /* try from rear */
                   if (vm_physmem[lcv].avail_end == vm_physmem[lcv].end &&
                       vm_physmem[lcv].avail_start < vm_physmem[lcv].avail_end) {
                           *paddrp = ptoa(vm_physmem[lcv].avail_end - 1);
                           vm_physmem[lcv].avail_end--;
                           vm_physmem[lcv].end--;
                           /* nothing left?   nuke it */
                           if (vm_physmem[lcv].avail_end ==
                               vm_physmem[lcv].start) {
                                   if (vm_nphysseg == 1)
                                       panic("uvm_page_physget: out of memory!");
                                   vm_nphysseg--;
                                   for (x = lcv ; x < vm_nphysseg ; x++)
                                           /* structure copy */
                                           vm_physmem[x] = vm_physmem[x+1];
                           }
                           return (TRUE);
                   }
           }
   
           /* pass2: forget about matching ends, just allocate something */
   #if (VM_PHYSSEG_STRAT == VM_PSTRAT_BIGFIRST)
           for (lcv = vm_nphysseg - 1 ; lcv >= 0 ; lcv--)
   #else
           for (lcv = 0 ; lcv < vm_nphysseg ; lcv++)
   #endif
           {
   
                   /* any room in this bank? */
                   if (vm_physmem[lcv].avail_start >= vm_physmem[lcv].avail_end)
                           continue;  /* nope */
   
                   *paddrp = ptoa(vm_physmem[lcv].avail_start);
                   vm_physmem[lcv].avail_start++;
                   /* truncate! */
                   vm_physmem[lcv].start = vm_physmem[lcv].avail_start;
   
                   /* nothing left?   nuke it */
                   if (vm_physmem[lcv].avail_start == vm_physmem[lcv].end) {
                           if (vm_nphysseg == 1)
                                   panic("uvm_page_physget: out of memory!");
                           vm_nphysseg--;
                           for (x = lcv ; x < vm_nphysseg ; x++)
                                   /* structure copy */
                                   vm_physmem[x] = vm_physmem[x+1];
                   }
                   return (TRUE);
           }
   
           return (FALSE);        /* whoops! */
   }
   
   boolean_t
   uvm_page_physget(paddrp)
           paddr_t *paddrp;
   {
           int i;
   
           /* try in the order of freelist preference */
           for (i = 0; i < VM_NFREELIST; i++)
                   if (uvm_page_physget_freelist(paddrp, i) == TRUE)
                           return (TRUE);
           return (FALSE);
   }
   #endif /* PMAP_STEAL_MEMORY */
   
   /*
    * uvm_page_physload: load physical memory into VM system
    *
    * => all args are PFs
    * => all pages in start/end get vm_page structures
    * => areas marked by avail_start/avail_end get added to the free page pool
    * => we are limited to VM_PHYSSEG_MAX physical memory segments
    */
   
   void
   uvm_page_physload(start, end, avail_start, avail_end, free_list)
           paddr_t start, end, avail_start, avail_end;
           int free_list;
   {
           int preload, lcv;
           psize_t npages;
           struct vm_page *pgs;
           struct vm_physseg *ps;
   
           if (uvmexp.pagesize == 0)
                   panic("uvm_page_physload: page size not set!");
           if (free_list >= VM_NFREELIST || free_list < VM_FREELIST_DEFAULT)
                   panic("uvm_page_physload: bad free list %d", free_list);
           if (start >= end)
                   panic("uvm_page_physload: start >= end");
   
           /*
            * do we have room?
            */
   
           if (vm_nphysseg == VM_PHYSSEG_MAX) {
                   printf("uvm_page_physload: unable to load physical memory "
                       "segment\n");
                   printf("\t%d segments allocated, ignoring 0x%llx -> 0x%llx\n",
                       VM_PHYSSEG_MAX, (long long)start, (long long)end);
                   printf("\tincrease VM_PHYSSEG_MAX\n");
                   return;
           }
   
           /*
            * check to see if this is a "preload" (i.e. uvm_mem_init hasn't been
            * called yet, so malloc is not available).
            */
   
           for (lcv = 0 ; lcv < vm_nphysseg ; lcv++) {
                   if (vm_physmem[lcv].pgs)
                           break;
           }
           preload = (lcv == vm_nphysseg);
   
           /*
            * if VM is already running, attempt to malloc() vm_page structures
            */
   
           if (!preload) {
   #if defined(VM_PHYSSEG_NOADD)
                   panic("uvm_page_physload: tried to add RAM after vm_mem_init");
   #else
                   /* XXXCDC: need some sort of lockout for this case */
                   paddr_t paddr;
                   npages = end - start;  /* # of pages */
                   pgs = malloc(sizeof(struct vm_page) * npages,
                       M_VMPAGE, M_NOWAIT);
                   if (pgs == NULL) {
                           printf("uvm_page_physload: can not malloc vm_page "
                               "structs for segment\n");
                           printf("\tignoring 0x%lx -> 0x%lx\n", start, end);
                           return;
                   }
                   /* zero data, init phys_addr and free_list, and free pages */
                   memset(pgs, 0, sizeof(struct vm_page) * npages);
                   for (lcv = 0, paddr = ptoa(start) ;
                                    lcv < npages ; lcv++, paddr += PAGE_SIZE) {
                           pgs[lcv].phys_addr = paddr;
                           pgs[lcv].free_list = free_list;
                           if (atop(paddr) >= avail_start &&
                               atop(paddr) <= avail_end)
                                   uvm_pagefree(&pgs[lcv]);
                   }
                   /* XXXCDC: incomplete: need to update uvmexp.free, what else? */
                   /* XXXCDC: need hook to tell pmap to rebuild pv_list, etc... */
   #endif
           } else {
                   pgs = NULL;
                   npages = 0;
           }
   
           /*
            * now insert us in the proper place in vm_physmem[]
            */
   
   #if (VM_PHYSSEG_STRAT == VM_PSTRAT_RANDOM)
           /* random: put it at the end (easy!) */
           ps = &vm_physmem[vm_nphysseg];
   #elif (VM_PHYSSEG_STRAT == VM_PSTRAT_BSEARCH)
           {
                   int x;
                   /* sort by address for binary search */
                   for (lcv = 0 ; lcv < vm_nphysseg ; lcv++)
                           if (start < vm_physmem[lcv].start)
                                   break;
                   ps = &vm_physmem[lcv];
                   /* move back other entries, if necessary ... */
                   for (x = vm_nphysseg ; x > lcv ; x--)
                           /* structure copy */
                           vm_physmem[x] = vm_physmem[x - 1];
           }
   #elif (VM_PHYSSEG_STRAT == VM_PSTRAT_BIGFIRST)
           {
                   int x;
                   /* sort by largest segment first */
                   for (lcv = 0 ; lcv < vm_nphysseg ; lcv++)
                           if ((end - start) >
                               (vm_physmem[lcv].end - vm_physmem[lcv].start))
                                   break;
                   ps = &vm_physmem[lcv];
                   /* move back other entries, if necessary ... */
                   for (x = vm_nphysseg ; x > lcv ; x--)
                           /* structure copy */
                           vm_physmem[x] = vm_physmem[x - 1];
           }
   #else
           panic("uvm_page_physload: unknown physseg strategy selected!");
   #endif
   
           ps->start = start;
           ps->end = end;
           ps->avail_start = avail_start;
           ps->avail_end = avail_end;
           if (preload) {
                   ps->pgs = NULL;
           } else {
                   ps->pgs = pgs;
                   ps->lastpg = pgs + npages - 1;
           }
           ps->free_list = free_list;
           vm_nphysseg++;
   
           if (!preload)
                   uvm_page_rehash();
   }
   
   /*
    * uvm_page_rehash: reallocate hash table based on number of free pages.
    */
   
   void
   uvm_page_rehash()
   {
           int freepages, lcv, bucketcount, oldcount;
           struct pglist *newbuckets, *oldbuckets;
           struct vm_page *pg;
           size_t newsize, oldsize;
   
           /*
            * compute number of pages that can go in the free pool
            */
   
           freepages = 0;
           for (lcv = 0 ; lcv < vm_nphysseg ; lcv++)
                   freepages +=
                       (vm_physmem[lcv].avail_end - vm_physmem[lcv].avail_start);
   
           /*
            * compute number of buckets needed for this number of pages
            */
   
           bucketcount = 1;
           while (bucketcount < freepages)
                   bucketcount = bucketcount * 2;
   
           /*
            * compute the size of the current table and new table.
            */
   
           oldbuckets = uvm.page_hash;
           oldcount = uvm.page_nhash;
           oldsize = round_page(sizeof(struct pglist) * oldcount);
           newsize = round_page(sizeof(struct pglist) * bucketcount);
   
           /*
            * allocate the new buckets
            */
   
           newbuckets = (struct pglist *) uvm_km_alloc(kernel_map, newsize);
           if (newbuckets == NULL) {
                   printf("uvm_page_physrehash: WARNING: could not grow page "
                       "hash table\n");
                   return;
           }
           for (lcv = 0 ; lcv < bucketcount ; lcv++)
                   TAILQ_INIT(&newbuckets[lcv]);
   
           /*
            * now replace the old buckets with the new ones and rehash everything
            */
   
           simple_lock(&uvm.hashlock);
           uvm.page_hash = newbuckets;
           uvm.page_nhash = bucketcount;
           uvm.page_hashmask = bucketcount - 1;  /* power of 2 */
   
           /* ... and rehash */
           for (lcv = 0 ; lcv < oldcount ; lcv++) {
                   while ((pg = oldbuckets[lcv].tqh_first) != NULL) {
                           TAILQ_REMOVE(&oldbuckets[lcv], pg, hashq);
                           TAILQ_INSERT_TAIL(
                             &uvm.page_hash[uvm_pagehash(pg->uobject, pg->offset)],
                             pg, hashq);
                   }
           }
           simple_unlock(&uvm.hashlock);
   
           /*
            * free old bucket array if is not the boot-time table
            */
   
           if (oldbuckets != &uvm_bootbucket)
                   uvm_km_free(kernel_map, (vaddr_t) oldbuckets, oldsize);
   }
   
   /*
    * uvm_page_recolor: Recolor the pages if the new bucket count is
    * larger than the old one.
    */
   
   void
   uvm_page_recolor(int newncolors)
   {
           struct pgflbucket *bucketarray, *oldbucketarray;
           struct pgfreelist pgfl;
           struct vm_page *pg;
           vsize_t bucketcount;
           int s, lcv, color, i, ocolors;
   
           if (newncolors <= uvmexp.ncolors)
                   return;
   
           if (uvm.page_init_done == FALSE) {
                   uvmexp.ncolors = newncolors;
                   return;
           }
   
           bucketcount = newncolors * VM_NFREELIST;
           bucketarray = malloc(bucketcount * sizeof(struct pgflbucket),
               M_VMPAGE, M_NOWAIT);
           if (bucketarray == NULL) {
                   printf("WARNING: unable to allocate %ld page color buckets\n",
                       (long) bucketcount);
                   return;
           }
   
           s = uvm_lock_fpageq();
   
           /* Make sure we should still do this. */
           if (newncolors <= uvmexp.ncolors) {
                   uvm_unlock_fpageq(s);
                   free(bucketarray, M_VMPAGE);
                   return;
           }
   
           oldbucketarray = uvm.page_free[0].pgfl_buckets;
           ocolors = uvmexp.ncolors;
   
           uvmexp.ncolors = newncolors;
           uvmexp.colormask = uvmexp.ncolors - 1;
   
           for (lcv = 0; lcv < VM_NFREELIST; lcv++) {
                   pgfl.pgfl_buckets = (bucketarray + (lcv * newncolors));
                   uvm_page_init_buckets(&pgfl);
                   for (color = 0; color < ocolors; color++) {
                           for (i = 0; i < PGFL_NQUEUES; i++) {
                                   while ((pg = TAILQ_FIRST(&uvm.page_free[
                                       lcv].pgfl_buckets[color].pgfl_queues[i]))
                                       != NULL) {
                                           TAILQ_REMOVE(&uvm.page_free[
                                               lcv].pgfl_buckets[
                                               color].pgfl_queues[i], pg, pageq);
                                           TAILQ_INSERT_TAIL(&pgfl.pgfl_buckets[
                                               VM_PGCOLOR_BUCKET(pg)].pgfl_queues[
                                               i], pg, pageq);
                                   }
                           }
                   }
                   uvm.page_free[lcv].pgfl_buckets = pgfl.pgfl_buckets;
           }
   
           if (have_recolored_pages) {
                   uvm_unlock_fpageq(s);
                   free(oldbucketarray, M_VMPAGE);
                   return;
           }
   
           have_recolored_pages = TRUE;
           uvm_unlock_fpageq(s);
   }
   
   /*
    * uvm_pagealloc_pgfl: helper routine for uvm_pagealloc_strat
    */
   
   static __inline struct vm_page *
   uvm_pagealloc_pgfl(struct pgfreelist *pgfl, int try1, int try2,
       int *trycolorp)
   {
           struct pglist *freeq;
           struct vm_page *pg;
           int color, trycolor = *trycolorp;
  
          color = trycolor;
          do {
                  if ((pg = TAILQ_FIRST((freeq =
                      &pgfl->pgfl_buckets[color].pgfl_queues[try1]))) != NULL)
                          goto gotit;
                  if ((pg = TAILQ_FIRST((freeq =
                      &pgfl->pgfl_buckets[color].pgfl_queues[try2]))) != NULL)
                          goto gotit;
                  color = (color + 1) & uvmexp.colormask;
          } while (color != trycolor);
  
          return (NULL);
  
   gotit:
          TAILQ_REMOVE(freeq, pg, pageq);
          uvmexp.free--;
  
          /* update zero'd page count */
          if (pg->flags & PG_ZERO)
                  uvmexp.zeropages--;
  
          if (color == trycolor)
                  uvmexp.colorhit++;
          else {
                  uvmexp.colormiss++;
                  *trycolorp = color;
          }
  
          return (pg);
  }
  
  /*
   * uvm_pagealloc_strat: allocate vm_page from a particular free list.
   *
   * => return null if no pages free
   * => wake up pagedaemon if number of free pages drops below low water mark
   * => if obj != NULL, obj must be locked (to put in hash)
   * => if anon != NULL, anon must be locked (to put in anon)
   * => only one of obj or anon can be non-null
   * => caller must activate/deactivate page if it is not wired.
   * => free_list is ignored if strat == UVM_PGA_STRAT_NORMAL.
   * => policy decision: it is more important to pull a page off of the
   *      appropriate priority free list than it is to get a zero'd or
   *      unknown contents page.  This is because we live with the
   *      consequences of a bad free list decision for the entire
   *      lifetime of the page, e.g. if the page comes from memory that
   *      is slower to access.
   */
  
  struct vm_page *
  uvm_pagealloc_strat(obj, off, anon, flags, strat, free_list)
          struct uvm_object *obj;
          voff_t off;
          int flags;
          struct vm_anon *anon;
          int strat, free_list;
  {
          int lcv, try1, try2, s, zeroit = 0, color;
          struct vm_page *pg;
          boolean_t use_reserve;
  
          KASSERT(obj == NULL || anon == NULL);
          KASSERT(off == trunc_page(off));
          LOCK_ASSERT(obj == NULL || simple_lock_held(&obj->vmobjlock));
          LOCK_ASSERT(anon == NULL || simple_lock_held(&anon->an_lock));
  
          s = uvm_lock_fpageq();
  
          /*
           * This implements a global round-robin page coloring
           * algorithm.
           *
           * XXXJRT: Should we make the `nextcolor' per-CPU?
           * XXXJRT: What about virtually-indexed caches?
           */
  
          color = uvm.page_free_nextcolor;
  
          /*
           * check to see if we need to generate some free pages waking
           * the pagedaemon.
           */
  
          UVM_KICK_PDAEMON();
  
          /*
           * fail if any of these conditions is true:
           * [1]  there really are no free pages, or
           * [2]  only kernel "reserved" pages remain and
           *        the page isn't being allocated to a kernel object.
           * [3]  only pagedaemon "reserved" pages remain and
           *        the requestor isn't the pagedaemon.
           */
  
          use_reserve = (flags & UVM_PGA_USERESERVE) ||
                  (obj && UVM_OBJ_IS_KERN_OBJECT(obj));
          if ((uvmexp.free <= uvmexp.reserve_kernel && !use_reserve) ||
              (uvmexp.free <= uvmexp.reserve_pagedaemon &&
               !(use_reserve && curproc == uvm.pagedaemon_proc)))
                  goto fail;
  
  #if PGFL_NQUEUES != 2
  #error uvm_pagealloc_strat needs to be updated
  #endif
  
          /*
           * If we want a zero'd page, try the ZEROS queue first, otherwise
           * we try the UNKNOWN queue first.
           */
          if (flags & UVM_PGA_ZERO) {
                  try1 = PGFL_ZEROS;
                  try2 = PGFL_UNKNOWN;
          } else {
                  try1 = PGFL_UNKNOWN;
                  try2 = PGFL_ZEROS;
          }
  
   again:
          switch (strat) {
          case UVM_PGA_STRAT_NORMAL:
                  /* Check all freelists in descending priority order. */
                  for (lcv = 0; lcv < VM_NFREELIST; lcv++) {
                          pg = uvm_pagealloc_pgfl(&uvm.page_free[lcv],
                              try1, try2, &color);
                          if (pg != NULL)
                                  goto gotit;
                  }
  
                  /* No pages free! */
                  goto fail;
  
          case UVM_PGA_STRAT_ONLY:
          case UVM_PGA_STRAT_FALLBACK:
                  /* Attempt to allocate from the specified free list. */
                  KASSERT(free_list >= 0 && free_list < VM_NFREELIST);
                  pg = uvm_pagealloc_pgfl(&uvm.page_free[free_list],
                      try1, try2, &color);
                  if (pg != NULL)
                          goto gotit;
  
                  /* Fall back, if possible. */
                  if (strat == UVM_PGA_STRAT_FALLBACK) {
                          strat = UVM_PGA_STRAT_NORMAL;
                          goto again;
                  }
  
                  /* No pages free! */
                  goto fail;
  
          default:
                  panic("uvm_pagealloc_strat: bad strat %d", strat);
                  /* NOTREACHED */
          }
  
   gotit:
          /*
           * We now know which color we actually allocated from; set
           * the next color accordingly.
           */
  
          uvm.page_free_nextcolor = (color + 1) & uvmexp.colormask;
  
          /*
           * update allocation statistics and remember if we have to
           * zero the page
           */
  
          if (flags & UVM_PGA_ZERO) {
                  if (pg->flags & PG_ZERO) {
                          uvmexp.pga_zerohit++;
                          zeroit = 0;
                  } else {
                          uvmexp.pga_zeromiss++;
                          zeroit = 1;
                  }
          }
          uvm_unlock_fpageq(s);
  
          pg->offset = off;
          pg->uobject = obj;
          pg->uanon = anon;
          pg->flags = PG_BUSY|PG_CLEAN|PG_FAKE;
          if (anon) {
                  anon->u.an_page = pg;
                  pg->pqflags = PQ_ANON;
                  uvmexp.anonpages++;
          } else {
                  if (obj) {
                          uvm_pageinsert(pg);
                  }
                  pg->pqflags = 0;
          }
  #if defined(UVM_PAGE_TRKOWN)
          pg->owner_tag = NULL;
  #endif
          UVM_PAGE_OWN(pg, "new alloc");
  
          if (flags & UVM_PGA_ZERO) {
                  /*
                   * A zero'd page is not clean.  If we got a page not already
                   * zero'd, then we have to zero it ourselves.
                   */
                  pg->flags &= ~PG_CLEAN;
                  if (zeroit)
                          pmap_zero_page(VM_PAGE_TO_PHYS(pg));
          }
  
          return(pg);
  
   fail:
          uvm_unlock_fpageq(s);
          return (NULL);
  }
  
  /*
   * uvm_pagereplace: replace a page with another
   *
   * => object must be locked
   */
  
  void
  uvm_pagereplace(oldpg, newpg)
          struct vm_page *oldpg;
          struct vm_page *newpg;
  {
  
          KASSERT((oldpg->flags & PG_TABLED) != 0);
          KASSERT(oldpg->uobject != NULL);
          KASSERT((newpg->flags & PG_TABLED) == 0);
          KASSERT(newpg->uobject == NULL);
          LOCK_ASSERT(simple_lock_held(&oldpg->uobject->vmobjlock));
  
          newpg->uobject = oldpg->uobject;
          newpg->offset = oldpg->offset;
  
          uvm_pageinsert_after(newpg, oldpg);
          uvm_pageremove(oldpg);
  }
  
  /*
   * uvm_pagerealloc: reallocate a page from one object to another
   *
   * => both objects must be locked
   */
  
  void
  uvm_pagerealloc(pg, newobj, newoff)
          struct vm_page *pg;
          struct uvm_object *newobj;
          voff_t newoff;
  {
          /*
           * remove it from the old object
           */
  
          if (pg->uobject) {
                  uvm_pageremove(pg);
          }
  
          /*
           * put it in the new object
           */
  
          if (newobj) {
                  pg->uobject = newobj;
                  pg->offset = newoff;
                  uvm_pageinsert(pg);
          }
  }
  
  #ifdef DEBUG
  /*
   * check if page is zero-filled
   *
   *  - called with free page queue lock held.
   */
  void
  uvm_pagezerocheck(struct vm_page *pg)
  {
          int *p, *ep;
  
          KASSERT(uvm_zerocheckkva != 0);
          LOCK_ASSERT(simple_lock_held(&uvm.fpageqlock));
  
          /*
           * XXX assuming pmap_kenter_pa and pmap_kremove never call
           * uvm page allocator.
           *
           * it might be better to have "CPU-local temporary map" pmap interface.
           */
          pmap_kenter_pa(uvm_zerocheckkva, VM_PAGE_TO_PHYS(pg), VM_PROT_READ);
          p = (int *)uvm_zerocheckkva;
          ep = (int *)((char *)p + PAGE_SIZE);
          pmap_update(pmap_kernel());
          while (p < ep) {
                  if (*p != 0)
                          panic("PG_ZERO page isn't zero-filled");
                  p++;
          }
          pmap_kremove(uvm_zerocheckkva, PAGE_SIZE);
  }
  #endif /* DEBUG */
  
  /*
   * uvm_pagefree: free page
   *
   * => erase page's identity (i.e. remove from hash/object)
   * => put page on free list
   * => caller must lock owning object (either anon or uvm_object)
   * => caller must lock page queues
   * => assumes all valid mappings of pg are gone
   */
  
  void
  uvm_pagefree(pg)
          struct vm_page *pg;
  {
          int s;
          struct pglist *pgfl;
          boolean_t iszero;
  
          KASSERT((pg->flags & PG_PAGEOUT) == 0);
          LOCK_ASSERT(simple_lock_held(&uvm.pageqlock) ||
                      (pg->pqflags & (PQ_ACTIVE|PQ_INACTIVE)) == 0);
          LOCK_ASSERT(pg->uobject == NULL ||
                      simple_lock_held(&pg->uobject->vmobjlock));
          LOCK_ASSERT(pg->uobject != NULL || pg->uanon == NULL ||
                      simple_lock_held(&pg->uanon->an_lock));
  
  #ifdef DEBUG
          if (pg->uobject == (void *)0xdeadbeef &&
              pg->uanon == (void *)0xdeadbeef) {
                  panic("uvm_pagefree: freeing free page %p", pg);
          }
  #endif /* DEBUG */
  
          /*
           * if the page is loaned, resolve the loan instead of freeing.
           */
  
          if (pg->loan_count) {
                  KASSERT(pg->wire_count == 0);
  
                  /*
                   * if the page is owned by an anon then we just want to
                   * drop anon ownership.  the kernel will free the page when
                   * it is done with it.  if the page is owned by an object,
                   * remove it from the object and mark it dirty for the benefit
                   * of possible anon owners.
                   *
                   * regardless of previous ownership, wakeup any waiters,
                   * unbusy the page, and we're done.
                   */
  
                  if (pg->uobject != NULL) {
                          uvm_pageremove(pg);
                          pg->flags &= ~PG_CLEAN;
                  } else if (pg->uanon != NULL) {
                          if ((pg->pqflags & PQ_ANON) == 0) {
                                  pg->loan_count--;
                          } else {
                                  pg->pqflags &= ~PQ_ANON;
                                  uvmexp.anonpages--;
                          }
                          pg->uanon->u.an_page = NULL;
                          pg->uanon = NULL;
                  }
                  if (pg->flags & PG_WANTED) {
                          wakeup(pg);
                  }
                  pg->flags &= ~(PG_WANTED|PG_BUSY|PG_RELEASED|PG_PAGER1);
  #ifdef UVM_PAGE_TRKOWN
                  pg->owner_tag = NULL;
  #endif
                  if (pg->loan_count) {
                          uvm_pagedequeue(pg);
                          return;
                  }
          }
  
          /*
           * remove page from its object or anon.
           */
  
          if (pg->uobject != NULL) {
                  uvm_pageremove(pg);
          } else if (pg->uanon != NULL) {
                  pg->uanon->u.an_page = NULL;
                  uvmexp.anonpages--;
          }
  
          /*
           * now remove the page from the queues.
           */
  
          uvm_pagedequeue(pg);
  
          /*
           * if the page was wired, unwire it now.
           */
  
          if (pg->wire_count) {
                  pg->wire_count = 0;
                  uvmexp.wired--;
          }
  
          /*
           * and put on free queue
           */
  
          iszero = (pg->flags & PG_ZERO);
          pgfl = &uvm.page_free[uvm_page_lookup_freelist(pg)].
              pgfl_buckets[VM_PGCOLOR_BUCKET(pg)].
              pgfl_queues[iszero ? PGFL_ZEROS : PGFL_UNKNOWN];
  
          pg->pqflags = PQ_FREE;
  #ifdef DEBUG
          pg->uobject = (void *)0xdeadbeef;
          pg->offset = 0xdeadbeef;
          pg->uanon = (void *)0xdeadbeef;
  #endif
  
          s = uvm_lock_fpageq();
  
  #ifdef DEBUG
          if (iszero)
                  uvm_pagezerocheck(pg);
  #endif /* DEBUG */
  
          TAILQ_INSERT_TAIL(pgfl, pg, pageq);
          uvmexp.free++;
          if (iszero)
                  uvmexp.zeropages++;
  
          if (uvmexp.zeropages < UVM_PAGEZERO_TARGET)
                  uvm.page_idle_zero = vm_page_zero_enable;
  
          uvm_unlock_fpageq(s);
  }
  
  /*
   * uvm_page_unbusy: unbusy an array of pages.
   *
   * => pages must either all belong to the same object, or all belong to anons.
   * => if pages are object-owned, object must be locked.
   * => if pages are anon-owned, anons must be locked.
   * => caller must lock page queues if pages may be released.
   * => caller must make sure that anon-owned pages are not PG_RELEASED.
   */
  
  void
  uvm_page_unbusy(pgs, npgs)
          struct vm_page **pgs;
          int npgs;
  {
          struct vm_page *pg;
          int i;
          UVMHIST_FUNC("uvm_page_unbusy"); UVMHIST_CALLED(ubchist);
  
          for (i = 0; i < npgs; i++) {
                  pg = pgs[i];
                  if (pg == NULL || pg == PGO_DONTCARE) {
                          continue;
                  }
  
                  LOCK_ASSERT(pg->uobject == NULL ||
                      simple_lock_held(&pg->uobject->vmobjlock));
                  LOCK_ASSERT(pg->uobject != NULL ||
                      (pg->uanon != NULL &&
                      simple_lock_held(&pg->uanon->an_lock)));
  
                  KASSERT(pg->flags & PG_BUSY);
                  KASSERT((pg->flags & PG_PAGEOUT) == 0);
                  if (pg->flags & PG_WANTED) {
                          wakeup(pg);
                  }
                  if (pg->flags & PG_RELEASED) {
                          UVMHIST_LOG(ubchist, "releasing pg %p", pg,0,0,0);
                          KASSERT(pg->uobject != NULL ||
                              (pg->uanon != NULL && pg->uanon->an_ref > 0));
                          pg->flags &= ~PG_RELEASED;
                          uvm_pagefree(pg);
                  } else {
                          UVMHIST_LOG(ubchist, "unbusying pg %p", pg,0,0,0);
                          pg->flags &= ~(PG_WANTED|PG_BUSY);
                          UVM_PAGE_OWN(pg, NULL);
                  }
          }
  }
  
  #if defined(UVM_PAGE_TRKOWN)
  /*
   * uvm_page_own: set or release page ownership
   *
   * => this is a debugging function that keeps track of who sets PG_BUSY
   *      and where they do it.   it can be used to track down problems
   *      such a process setting "PG_BUSY" and never releasing it.
   * => page's object [if any] must be locked
   * => if "tag" is NULL then we are releasing page ownership
   */
  void
  uvm_page_own(pg, tag)
          struct vm_page *pg;
          char *tag;
  {
          KASSERT((pg->flags & (PG_PAGEOUT|PG_RELEASED)) == 0);
  
          /* gain ownership? */
          if (tag) {
                  if (pg->owner_tag) {
                          printf("uvm_page_own: page %p already owned "
                              "by proc %d [%s]\n", pg,
                              pg->owner, pg->owner_tag);
                          panic("uvm_page_own");
                  }
                  pg->owner = (curproc) ? curproc->p_pid :  (pid_t) -1;
                  pg->owner_tag = tag;
                  return;
          }
  
          /* drop ownership */
          if (pg->owner_tag == NULL) {
                  printf("uvm_page_own: dropping ownership of an non-owned "
                      "page (%p)\n", pg);
                  panic("uvm_page_own");
          }
          KASSERT((pg->pqflags & (PQ_ACTIVE|PQ_INACTIVE)) ||
              (pg->uanon == NULL && pg->uobject == NULL) ||
              pg->uobject == uvm.kernel_object ||
              pg->wire_count > 0 ||
              (pg->loan_count == 1 && pg->uanon == NULL) ||
              pg->loan_count > 1);
          pg->owner_tag = NULL;
  }
  #endif
  
  /*
   * uvm_pageidlezero: zero free pages while the system is idle.
   *
   * => try to complete one color bucket at a time, to reduce our impact
   *      on the CPU cache.
   * => we loop until we either reach the target or whichqs indicates that
   *      there is a process ready to run.
   */
  void
  uvm_pageidlezero()
  {
          struct vm_page *pg;
          struct pgfreelist *pgfl;
          int free_list, s, firstbucket;
          static int nextbucket;
  
          s = uvm_lock_fpageq();
          firstbucket = nextbucket;
          do {
                  if (sched_whichqs != 0) {
                          uvm_unlock_fpageq(s);
                          return;
                  }
                  if (uvmexp.zeropages >= UVM_PAGEZERO_TARGET) {
                          uvm.page_idle_zero = FALSE;
                          uvm_unlock_fpageq(s);
                          return;
                  }
                  for (free_list = 0; free_list < VM_NFREELIST; free_list++) {
                          pgfl = &uvm.page_free[free_list];
                          while ((pg = TAILQ_FIRST(&pgfl->pgfl_buckets[
                              nextbucket].pgfl_queues[PGFL_UNKNOWN])) != NULL) {
                                  if (sched_whichqs != 0) {
                                          uvm_unlock_fpageq(s);
                                          return;
                                  }
  
                                  TAILQ_REMOVE(&pgfl->pgfl_buckets[
                                      nextbucket].pgfl_queues[PGFL_UNKNOWN],
                                      pg, pageq);
                                  uvmexp.free--;
                                  uvm_unlock_fpageq(s);
  #ifdef PMAP_PAGEIDLEZERO
                                  if (!PMAP_PAGEIDLEZERO(VM_PAGE_TO_PHYS(pg))) {
  
                                          /*
                                           * The machine-dependent code detected
                                           * some reason for us to abort zeroing
                                           * pages, probably because there is a
                                           * process now ready to run.
                                           */
  
                                          s = uvm_lock_fpageq();
                                          TAILQ_INSERT_HEAD(&pgfl->pgfl_buckets[
                                              nextbucket].pgfl_queues[
                                              PGFL_UNKNOWN], pg, pageq);
                                          uvmexp.free++;
                                          uvmexp.zeroaborts++;
                                          uvm_unlock_fpageq(s);
                                          return;
                                  }
  #else
                                  pmap_zero_page(VM_PAGE_TO_PHYS(pg));
  #endif /* PMAP_PAGEIDLEZERO */
                                  pg->flags |= PG_ZERO;
  
                                  s = uvm_lock_fpageq();
                                  TAILQ_INSERT_HEAD(&pgfl->pgfl_buckets[
                                      nextbucket].pgfl_queues[PGFL_ZEROS],
                                      pg, pageq);
                                  uvmexp.free++;
                                  uvmexp.zeropages++;
                          }
                  }
                  nextbucket = (nextbucket + 1) & uvmexp.colormask;
          } while (nextbucket != firstbucket);
          uvm_unlock_fpageq(s);
  }

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