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

     /*-
      * 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.
     *
     * The default pager is responsible for supplying backing store to unbacked
     * storage.  The backing store is usually swap so we just fall through to
     * the swap routines.  However, since swap metadata has not been assigned,
     * the swap routines assign and manage the swap backing store through the
     * vm_page->swapblk field.  The object is only converted when the page is 
     * physically freed after having been cleaned and even then vm_page->swapblk
     * is maintained whenever a resident page also has swap backing store.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/10.4/sys/vm/default_pager.c 310363 2016-12-21 11:32:08Z kib $");
    
    #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);
    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,
    };
    
    /*
     * no_pager_alloc just returns 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) {
                   VM_OBJECT_WLOCK(object);
                   object->cred = cred;
                   object->charge = size;
                   VM_OBJECT_WUNLOCK(object);
           }
           return (object);
   }
   
   /*
    * deallocate resources associated with default objects.   The default objects
    * have no special resources allocated to them, but the vm_page's being used
    * in this object might.  Still, we do not have to do anything - we will free
    * the swapblk in the underlying vm_page's when we free the vm_page or
    * garbage collect the vm_page cache list.
    */
   static void
   default_pager_dealloc(object)
           vm_object_t object;
   {
           /*
            * OBJT_DEFAULT objects have no special resources allocated to them.
            */
           object->type = OBJT_DEAD;
   }
   
   /*
    * Load pages from backing store.  Since OBJT_DEFAULT is converted to
    * OBJT_SWAP at the time a swap-backed vm_page_t is freed, we will never
    * see a vm_page with assigned swap here.
    */
   static int
   default_pager_getpages(object, m, count, reqpage)
           vm_object_t object;
           vm_page_t *m;
           int count;
           int reqpage;
   {
           return VM_PAGER_FAIL;
   }
   
   /*
    * Store pages to backing store.  We should assign swap and initiate
    * I/O.  We do not actually convert the object to OBJT_SWAP here.  The
    * object will be converted when the written-out vm_page_t is moved from the
    * cache to the free list.
    */
   static void
   default_pager_putpages(vm_object_t object, vm_page_t *m, int count,
       int flags, int *rtvals)
   {
   
           swappagerops.pgo_putpages(object, m, count, flags, rtvals);
   }
   
   /*
    * Tell us whether the backing store for the requested (object,index) is
    * synchronized.  i.e. tell us whether we can throw the page away and 
    * reload it later.  So, for example, if we are in the process of writing
    * the page to its backing store, or if no backing store has been assigned,
    * it is not yet synchronized.
    *
    * It is possible to have fully-synchronized swap assigned without the
    * object having been converted.  We just call swap_pager_haspage() to
    * deal with it since it must already deal with it plus deal with swap
    * meta-data structures.
    */
   static boolean_t
   default_pager_haspage(object, pindex, before, after)
           vm_object_t object;
           vm_pindex_t pindex;
           int *before;
           int *after;
   {
           return FALSE;
   }
   

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