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

     /*-
      * SPDX-License-Identifier: (BSD-3-Clause AND MIT-CMU)
      *
      * 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. 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.
     *
     *      from: @(#)vm_pager.c    8.6 (Berkeley) 1/12/94
     *
     *
     * Copyright (c) 1987, 1990 Carnegie-Mellon University.
     * All rights reserved.
     *
     * Authors: Avadis Tevanian, Jr., Michael Wayne Young
     *
     * 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.
     */
    
    /*
     *      Paging space routine stubs.  Emulates a matchmaker-like interface
     *      for builtin pagers.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/12.0/sys/vm/vm_pager.c 326403 2017-11-30 15:48:35Z pfg $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/vnode.h>
    #include <sys/bio.h>
    #include <sys/buf.h>
    #include <sys/ucred.h>
    #include <sys/malloc.h>
    #include <sys/rwlock.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    #include <vm/vm_pager.h>
    #include <vm/vm_extern.h>
    
    int cluster_pbuf_freecnt = -1;  /* unlimited to begin with */
    
    struct buf *swbuf;
    
    static int dead_pager_getpages(vm_object_t, vm_page_t *, int, int *, int *);
    static vm_object_t dead_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
        vm_ooffset_t, struct ucred *);
    static void dead_pager_putpages(vm_object_t, vm_page_t *, int, int, int *);
    static boolean_t dead_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
    static void dead_pager_dealloc(vm_object_t);
    
   static int
   dead_pager_getpages(vm_object_t obj, vm_page_t *ma, int count, int *rbehind,
       int *rahead)
   {
   
           return (VM_PAGER_FAIL);
   }
   
   static vm_object_t
   dead_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
       vm_ooffset_t off, struct ucred *cred)
   {
   
           return (NULL);
   }
   
   static void
   dead_pager_putpages(vm_object_t object, vm_page_t *m, int count,
       int flags, int *rtvals)
   {
           int i;
   
           for (i = 0; i < count; i++)
                   rtvals[i] = VM_PAGER_AGAIN;
   }
   
   static int
   dead_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *prev, int *next)
   {
   
           if (prev != NULL)
                   *prev = 0;
           if (next != NULL)
                   *next = 0;
           return (FALSE);
   }
   
   static void
   dead_pager_dealloc(vm_object_t object)
   {
   
   }
   
   static struct pagerops deadpagerops = {
           .pgo_alloc =    dead_pager_alloc,
           .pgo_dealloc =  dead_pager_dealloc,
           .pgo_getpages = dead_pager_getpages,
           .pgo_putpages = dead_pager_putpages,
           .pgo_haspage =  dead_pager_haspage,
   };
   
   struct pagerops *pagertab[] = {
           &defaultpagerops,       /* OBJT_DEFAULT */
           &swappagerops,          /* OBJT_SWAP */
           &vnodepagerops,         /* OBJT_VNODE */
           &devicepagerops,        /* OBJT_DEVICE */
           &physpagerops,          /* OBJT_PHYS */
           &deadpagerops,          /* OBJT_DEAD */
           &sgpagerops,            /* OBJT_SG */
           &mgtdevicepagerops,     /* OBJT_MGTDEVICE */
   };
   
   /*
    * Kernel address space for mapping pages.
    * Used by pagers where KVAs are needed for IO.
    *
    * XXX needs to be large enough to support the number of pending async
    * cleaning requests (NPENDINGIO == 64) * the maximum swap cluster size
    * (MAXPHYS == 64k) if you want to get the most efficiency.
    */
   struct mtx_padalign __exclusive_cache_line pbuf_mtx;
   static TAILQ_HEAD(swqueue, buf) bswlist;
   static int bswneeded;
   vm_offset_t swapbkva;           /* swap buffers kva */
   
   void
   vm_pager_init(void)
   {
           struct pagerops **pgops;
   
           TAILQ_INIT(&bswlist);
           /*
            * Initialize known pagers
            */
           for (pgops = pagertab; pgops < &pagertab[nitems(pagertab)]; pgops++)
                   if ((*pgops)->pgo_init != NULL)
                           (*(*pgops)->pgo_init)();
   }
   
   void
   vm_pager_bufferinit(void)
   {
           struct buf *bp;
           int i;
   
           mtx_init(&pbuf_mtx, "pbuf mutex", NULL, MTX_DEF);
           bp = swbuf;
           /*
            * Now set up swap and physical I/O buffer headers.
            */
           for (i = 0; i < nswbuf; i++, bp++) {
                   TAILQ_INSERT_HEAD(&bswlist, bp, b_freelist);
                   BUF_LOCKINIT(bp);
                   LIST_INIT(&bp->b_dep);
                   bp->b_rcred = bp->b_wcred = NOCRED;
                   bp->b_xflags = 0;
           }
   
           cluster_pbuf_freecnt = nswbuf / 2;
           vnode_pbuf_freecnt = nswbuf / 2 + 1;
           vnode_async_pbuf_freecnt = nswbuf / 2;
   }
   
   /*
    * Allocate an instance of a pager of the given type.
    * Size, protection and offset parameters are passed in for pagers that
    * need to perform page-level validation (e.g. the device pager).
    */
   vm_object_t
   vm_pager_allocate(objtype_t type, void *handle, vm_ooffset_t size,
       vm_prot_t prot, vm_ooffset_t off, struct ucred *cred)
   {
           vm_object_t ret;
           struct pagerops *ops;
   
           ops = pagertab[type];
           if (ops)
                   ret = (*ops->pgo_alloc)(handle, size, prot, off, cred);
           else
                   ret = NULL;
           return (ret);
   }
   
   /*
    *      The object must be locked.
    */
   void
   vm_pager_deallocate(vm_object_t object)
   {
   
           VM_OBJECT_ASSERT_WLOCKED(object);
           (*pagertab[object->type]->pgo_dealloc) (object);
   }
   
   static void
   vm_pager_assert_in(vm_object_t object, vm_page_t *m, int count)
   {
   #ifdef INVARIANTS
   
           VM_OBJECT_ASSERT_WLOCKED(object);
           KASSERT(count > 0, ("%s: 0 count", __func__));
           /*
            * All pages must be busied, not mapped, not fully valid,
            * not dirty and belong to the proper object.
            */
           for (int i = 0 ; i < count; i++) {
                   if (m[i] == bogus_page)
                           continue;
                   vm_page_assert_xbusied(m[i]);
                   KASSERT(!pmap_page_is_mapped(m[i]),
                       ("%s: page %p is mapped", __func__, m[i]));
                   KASSERT(m[i]->valid != VM_PAGE_BITS_ALL,
                       ("%s: request for a valid page %p", __func__, m[i]));
                   KASSERT(m[i]->dirty == 0,
                       ("%s: page %p is dirty", __func__, m[i]));
                   KASSERT(m[i]->object == object,
                       ("%s: wrong object %p/%p", __func__, object, m[i]->object));
           }
   #endif
   }
   
   /*
    * Page in the pages for the object using its associated pager.
    * The requested page must be fully valid on successful return.
    */
   int
   vm_pager_get_pages(vm_object_t object, vm_page_t *m, int count, int *rbehind,
       int *rahead)
   {
   #ifdef INVARIANTS
           vm_pindex_t pindex = m[0]->pindex;
   #endif
           int r;
   
           vm_pager_assert_in(object, m, count);
   
           r = (*pagertab[object->type]->pgo_getpages)(object, m, count, rbehind,
               rahead);
           if (r != VM_PAGER_OK)
                   return (r);
   
           for (int i = 0; i < count; i++) {
                   /*
                    * If pager has replaced a page, assert that it had
                    * updated the array.
                    */
                   KASSERT(m[i] == vm_page_lookup(object, pindex++),
                       ("%s: mismatch page %p pindex %ju", __func__,
                       m[i], (uintmax_t )pindex - 1));
                   /*
                    * Zero out partially filled data.
                    */
                   if (m[i]->valid != VM_PAGE_BITS_ALL)
                           vm_page_zero_invalid(m[i], TRUE);
           }
           return (VM_PAGER_OK);
   }
   
   int
   vm_pager_get_pages_async(vm_object_t object, vm_page_t *m, int count,
       int *rbehind, int *rahead, pgo_getpages_iodone_t iodone, void *arg)
   {
   
           vm_pager_assert_in(object, m, count);
   
           return ((*pagertab[object->type]->pgo_getpages_async)(object, m,
               count, rbehind, rahead, iodone, arg));
   }
   
   /*
    * vm_pager_put_pages() - inline, see vm/vm_pager.h
    * vm_pager_has_page() - inline, see vm/vm_pager.h
    */
   
   /*
    * Search the specified pager object list for an object with the
    * specified handle.  If an object with the specified handle is found,
    * increase its reference count and return it.  Otherwise, return NULL.
    *
    * The pager object list must be locked.
    */
   vm_object_t
   vm_pager_object_lookup(struct pagerlst *pg_list, void *handle)
   {
           vm_object_t object;
   
           TAILQ_FOREACH(object, pg_list, pager_object_list) {
                   if (object->handle == handle) {
                           VM_OBJECT_WLOCK(object);
                           if ((object->flags & OBJ_DEAD) == 0) {
                                   vm_object_reference_locked(object);
                                   VM_OBJECT_WUNLOCK(object);
                                   break;
                           }
                           VM_OBJECT_WUNLOCK(object);
                   }
           }
           return (object);
   }
   
   /*
    * initialize a physical buffer
    */
   
   /*
    * XXX This probably belongs in vfs_bio.c
    */
   static void
   initpbuf(struct buf *bp)
   {
   
           KASSERT(bp->b_bufobj == NULL, ("initpbuf with bufobj"));
           KASSERT(bp->b_vp == NULL, ("initpbuf with vp"));
           bp->b_rcred = NOCRED;
           bp->b_wcred = NOCRED;
           bp->b_qindex = 0;       /* On no queue (QUEUE_NONE) */
           bp->b_kvabase = (caddr_t)(MAXPHYS * (bp - swbuf)) + swapbkva;
           bp->b_data = bp->b_kvabase;
           bp->b_kvasize = MAXPHYS;
           bp->b_flags = 0;
           bp->b_xflags = 0;
           bp->b_ioflags = 0;
           bp->b_iodone = NULL;
           bp->b_error = 0;
           BUF_LOCK(bp, LK_EXCLUSIVE, NULL);
           buf_track(bp, __func__);
   }
   
   /*
    * allocate a physical buffer
    *
    *      There are a limited number (nswbuf) of physical buffers.  We need
    *      to make sure that no single subsystem is able to hog all of them,
    *      so each subsystem implements a counter which is typically initialized
    *      to 1/2 nswbuf.  getpbuf() decrements this counter in allocation and
    *      increments it on release, and blocks if the counter hits zero.  A
    *      subsystem may initialize the counter to -1 to disable the feature,
    *      but it must still be sure to match up all uses of getpbuf() with 
    *      relpbuf() using the same variable.
    *
    *      NOTE: pfreecnt can be NULL, but this 'feature' will be removed
    *      relatively soon when the rest of the subsystems get smart about it. XXX
    */
   struct buf *
   getpbuf(int *pfreecnt)
   {
           struct buf *bp;
   
           mtx_lock(&pbuf_mtx);
           for (;;) {
                   if (pfreecnt != NULL) {
                           while (*pfreecnt == 0) {
                                   msleep(pfreecnt, &pbuf_mtx, PVM, "wswbuf0", 0);
                           }
                   }
   
                   /* get a bp from the swap buffer header pool */
                   if ((bp = TAILQ_FIRST(&bswlist)) != NULL)
                           break;
   
                   bswneeded = 1;
                   msleep(&bswneeded, &pbuf_mtx, PVM, "wswbuf1", 0);
                   /* loop in case someone else grabbed one */
           }
           TAILQ_REMOVE(&bswlist, bp, b_freelist);
           if (pfreecnt)
                   --*pfreecnt;
           mtx_unlock(&pbuf_mtx);
           initpbuf(bp);
           return (bp);
   }
   
   /*
    * allocate a physical buffer, if one is available.
    *
    *      Note that there is no NULL hack here - all subsystems using this
    *      call understand how to use pfreecnt.
    */
   struct buf *
   trypbuf(int *pfreecnt)
   {
           struct buf *bp;
   
           mtx_lock(&pbuf_mtx);
           if (*pfreecnt == 0 || (bp = TAILQ_FIRST(&bswlist)) == NULL) {
                   mtx_unlock(&pbuf_mtx);
                   return NULL;
           }
           TAILQ_REMOVE(&bswlist, bp, b_freelist);
           --*pfreecnt;
           mtx_unlock(&pbuf_mtx);
           initpbuf(bp);
           return (bp);
   }
   
   /*
    * release a physical buffer
    *
    *      NOTE: pfreecnt can be NULL, but this 'feature' will be removed
    *      relatively soon when the rest of the subsystems get smart about it. XXX
    */
   void
   relpbuf(struct buf *bp, int *pfreecnt)
   {
   
           if (bp->b_rcred != NOCRED) {
                   crfree(bp->b_rcred);
                   bp->b_rcred = NOCRED;
           }
           if (bp->b_wcred != NOCRED) {
                   crfree(bp->b_wcred);
                   bp->b_wcred = NOCRED;
           }
   
           KASSERT(bp->b_vp == NULL, ("relpbuf with vp"));
           KASSERT(bp->b_bufobj == NULL, ("relpbuf with bufobj"));
   
           buf_track(bp, __func__);
           BUF_UNLOCK(bp);
   
           mtx_lock(&pbuf_mtx);
           TAILQ_INSERT_HEAD(&bswlist, bp, b_freelist);
   
           if (bswneeded) {
                   bswneeded = 0;
                   wakeup(&bswneeded);
           }
           if (pfreecnt) {
                   if (++*pfreecnt == 1)
                           wakeup(pfreecnt);
           }
           mtx_unlock(&pbuf_mtx);
   }
   
   /*
    * Associate a p-buffer with a vnode.
    *
    * Also sets B_PAGING flag to indicate that vnode is not fully associated
    * with the buffer.  i.e. the bp has not been linked into the vnode or
    * ref-counted.
    */
   void
   pbgetvp(struct vnode *vp, struct buf *bp)
   {
   
           KASSERT(bp->b_vp == NULL, ("pbgetvp: not free"));
           KASSERT(bp->b_bufobj == NULL, ("pbgetvp: not free (bufobj)"));
   
           bp->b_vp = vp;
           bp->b_flags |= B_PAGING;
           bp->b_bufobj = &vp->v_bufobj;
   }
   
   /*
    * Associate a p-buffer with a vnode.
    *
    * Also sets B_PAGING flag to indicate that vnode is not fully associated
    * with the buffer.  i.e. the bp has not been linked into the vnode or
    * ref-counted.
    */
   void
   pbgetbo(struct bufobj *bo, struct buf *bp)
   {
   
           KASSERT(bp->b_vp == NULL, ("pbgetbo: not free (vnode)"));
           KASSERT(bp->b_bufobj == NULL, ("pbgetbo: not free (bufobj)"));
   
           bp->b_flags |= B_PAGING;
           bp->b_bufobj = bo;
   }
   
   /*
    * Disassociate a p-buffer from a vnode.
    */
   void
   pbrelvp(struct buf *bp)
   {
   
           KASSERT(bp->b_vp != NULL, ("pbrelvp: NULL"));
           KASSERT(bp->b_bufobj != NULL, ("pbrelvp: NULL bufobj"));
           KASSERT((bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) == 0,
               ("pbrelvp: pager buf on vnode list."));
   
           bp->b_vp = NULL;
           bp->b_bufobj = NULL;
           bp->b_flags &= ~B_PAGING;
   }
   
   /*
    * Disassociate a p-buffer from a bufobj.
    */
   void
   pbrelbo(struct buf *bp)
   {
   
           KASSERT(bp->b_vp == NULL, ("pbrelbo: vnode"));
           KASSERT(bp->b_bufobj != NULL, ("pbrelbo: NULL bufobj"));
           KASSERT((bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) == 0,
               ("pbrelbo: pager buf on vnode list."));
   
           bp->b_bufobj = NULL;
           bp->b_flags &= ~B_PAGING;
   }

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