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

     /*-
      * SPDX-License-Identifier: BSD-4-Clause
      *
      * Copyright (c) 1995, David Greenman
      * All rights reserved.
      *
      * 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 David Greenman.
     * 4. The name of the author may not be used to endorse or promote products
     *    derived from this software without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/12.0/sys/vm/default_pager.c 326402 2017-11-30 15:45:42Z pfg $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/lock.h>
    #include <sys/proc.h>
    #include <sys/resourcevar.h>
    #include <sys/rwlock.h>
    
    #include <vm/vm.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    #include <vm/vm_pager.h>
    #include <vm/swap_pager.h>
    
    static vm_object_t      default_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
                                vm_ooffset_t, struct ucred *);
    static void             default_pager_dealloc(vm_object_t);
    static int              default_pager_getpages(vm_object_t, vm_page_t *, int,
                                int *, int *);
    static void             default_pager_putpages(vm_object_t, vm_page_t *, int, 
                                boolean_t, int *);
    static boolean_t        default_pager_haspage(vm_object_t, vm_pindex_t, int *, 
                                int *);
    
    /*
     * pagerops for OBJT_DEFAULT - "default pager".
     *
     * This pager handles anonymous (no handle) swap-backed memory, just
     * like the swap pager.  It allows several optimizations based on the
     * fact that no pages of a default object can be swapped out.  The
     * most important optimization is in vm_fault(), where the pager is
     * never asked for a non-resident page.  Instead, a freshly allocated
     * zeroed page is used.
     *
     * On the first request to page out a page from a default object, the
     * object is converted to swap pager type.
     */
    struct pagerops defaultpagerops = {
            .pgo_alloc =    default_pager_alloc,
            .pgo_dealloc =  default_pager_dealloc,
            .pgo_getpages = default_pager_getpages,
            .pgo_putpages = default_pager_putpages,
            .pgo_haspage =  default_pager_haspage,
    };
    
    /*
     * Return an initialized object.
     */
    static vm_object_t
    default_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
        vm_ooffset_t offset, struct ucred *cred)
    {
            vm_object_t object;
    
            if (handle != NULL)
                    panic("default_pager_alloc: handle specified");
            if (cred != NULL) {
                    if (!swap_reserve_by_cred(size, cred))
                            return (NULL);
                    crhold(cred);
            }
            object = vm_object_allocate(OBJT_DEFAULT,
                OFF_TO_IDX(round_page(offset + size)));
            if (cred != NULL) {
                   object->cred = cred;
                   object->charge = size;
           }
           return (object);
   }
   
   /*
    * Deallocate resources associated with the object.
    */
   static void
   default_pager_dealloc(vm_object_t object)
   {
   
           /* Reserved swap is released by vm_object_destroy(). */
           object->type = OBJT_DEAD;
   }
   
   /*
    * Load pages from backing store.
    */
   static int
   default_pager_getpages(vm_object_t object, vm_page_t *m, int count,
       int *rbehind, int *rahead)
   {
   
           /*
            * Since an OBJT_DEFAULT object is converted to OBJT_SWAP by the first
            * call to the putpages method, this function will never be called on
            * a vm_page with assigned swap.
            */
           return (VM_PAGER_FAIL);
   }
   
   /*
    * Store pages to backing store.
    */
   static void
   default_pager_putpages(vm_object_t object, vm_page_t *m, int count,
       int flags, int *rtvals)
   {
   
           /* The swap pager will convert the object to OBJT_SWAP. */
           swappagerops.pgo_putpages(object, m, count, flags, rtvals);
   }
   
   /*
    * Tell us whether the requested (object,index) is available from the object's
    * backing store.
    */
   static boolean_t
   default_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before,
       int *after)
   {
   
           /* An OBJT_DEFAULT object has no backing store. */
           return (FALSE);
   }
   

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