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

     /*      $NetBSD: uvm_aobj.c,v 1.156 2022/05/31 08:43:16 andvar Exp $    */
     
     /*
      * Copyright (c) 1998 Chuck Silvers, Charles D. Cranor and
      *                    Washington University.
      * 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.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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: Id: uvm_aobj.c,v 1.1.2.5 1998/02/06 05:14:38 chs Exp
     */
    
    /*
     * uvm_aobj.c: anonymous memory uvm_object pager
     *
     * author: Chuck Silvers <chuq@chuq.com>
     * started: Jan-1998
     *
     * - design mostly from Chuck Cranor
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: uvm_aobj.c,v 1.156 2022/05/31 08:43:16 andvar Exp $");
    
    #ifdef _KERNEL_OPT
    #include "opt_uvmhist.h"
    #endif
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/kmem.h>
    #include <sys/pool.h>
    #include <sys/atomic.h>
    
    #include <uvm/uvm.h>
    #include <uvm/uvm_page_array.h>
    
    /*
     * An anonymous UVM object (aobj) manages anonymous-memory.  In addition to
     * keeping the list of resident pages, it may also keep a list of allocated
     * swap blocks.  Depending on the size of the object, this list is either
     * stored in an array (small objects) or in a hash table (large objects).
     *
     * Lock order
     *
     *      uao_list_lock ->
     *              uvm_object::vmobjlock
     */
    
    /*
     * Note: for hash tables, we break the address space of the aobj into blocks
     * of UAO_SWHASH_CLUSTER_SIZE pages, which shall 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(idx)         ((idx) >> UAO_SWHASH_CLUSTER_SHIFT)
    #define UAO_SWHASH_ELT_PAGESLOT_IDX(idx) \
        ((idx) & (UAO_SWHASH_CLUSTER_SIZE - 1))
    
    /* Given an ELT and a page index, find the swap slot. */
    #define UAO_SWHASH_ELT_PAGESLOT(elt, idx) \
        ((elt)->slots[UAO_SWHASH_ELT_PAGESLOT_IDX(idx)])
    
    /* Given an ELT, return its pageidx base. */
    #define UAO_SWHASH_ELT_PAGEIDX_BASE(ELT) \
        ((elt)->tag << UAO_SWHASH_CLUSTER_SHIFT)
    
    /* The hash function. */
    #define UAO_SWHASH_HASH(aobj, idx) \
        (&(aobj)->u_swhash[(((idx) >> UAO_SWHASH_CLUSTER_SHIFT) \
        & (aobj)->u_swhashmask)])
    
    /*
     * The threshold which determines whether 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)
   
   /* The number of buckets in a hash, 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 */
           voff_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);
   
   /*
    * uao_swhash_elt_pool: pool of uao_swhash_elt structures.
    * Note: pages for this pool must not come from a pageable kernel map.
    */
   static struct pool      uao_swhash_elt_pool     __cacheline_aligned;
   
   /*
    * uvm_aobj: the actual anon-backed uvm_object
    *
    * => the uvm_object is at the top of the structure, this allows
    *   (struct uvm_aobj *) == (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, #pages, #refs */
           pgoff_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 */
                                    /*
                                     * hashtable of offset->swapslot mappings
                                     * (u_swhash is an array of bucket heads)
                                     */
           struct uao_swhash *u_swhash;
           u_long u_swhashmask;            /* mask for hashtable */
           LIST_ENTRY(uvm_aobj) u_list;    /* global list of aobjs */
           int u_freelist;           /* freelist to allocate pages from */
   };
   
   static void     uao_free(struct uvm_aobj *);
   static int      uao_get(struct uvm_object *, voff_t, struct vm_page **,
                       int *, int, vm_prot_t, int, int);
   static int      uao_put(struct uvm_object *, voff_t, voff_t, int);
   
   #if defined(VMSWAP)
   static struct uao_swhash_elt *uao_find_swhash_elt
       (struct uvm_aobj *, int, bool);
   
   static bool uao_pagein(struct uvm_aobj *, int, int);
   static bool uao_pagein_page(struct uvm_aobj *, int);
   #endif /* defined(VMSWAP) */
   
   static struct vm_page   *uao_pagealloc(struct uvm_object *, voff_t, int);
   
   /*
    * aobj_pager
    *
    * note that some functions (e.g. put) are handled elsewhere
    */
   
   const struct uvm_pagerops aobj_pager = {
           .pgo_reference = uao_reference,
           .pgo_detach = uao_detach,
           .pgo_get = uao_get,
           .pgo_put = uao_put,
   };
   
   /*
    * uao_list: global list of active aobjs, locked by uao_list_lock
    */
   
   static LIST_HEAD(aobjlist, uvm_aobj) uao_list   __cacheline_aligned;
   static kmutex_t         uao_list_lock           __cacheline_aligned;
   
   /*
    * hash table/array related functions
    */
   
   #if defined(VMSWAP)
   
   /*
    * 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(struct uvm_aobj *aobj, int pageidx, bool create)
   {
           struct uao_swhash *swhash;
           struct uao_swhash_elt *elt;
           voff_t page_tag;
   
           swhash = UAO_SWHASH_HASH(aobj, pageidx);
           page_tag = UAO_SWHASH_ELT_TAG(pageidx);
   
           /*
            * now search the bucket for the requested tag
            */
   
           LIST_FOREACH(elt, swhash, list) {
                   if (elt->tag == page_tag) {
                           return elt;
                   }
           }
           if (!create) {
                   return NULL;
           }
   
           /*
            * allocate a new entry for the bucket and init/insert it in
            */
   
           elt = pool_get(&uao_swhash_elt_pool, PR_NOWAIT);
           if (elt == NULL) {
                   return NULL;
           }
           LIST_INSERT_HEAD(swhash, elt, list);
           elt->tag = page_tag;
           elt->count = 0;
           memset(elt->slots, 0, sizeof(elt->slots));
           return elt;
   }
   
   /*
    * uao_find_swslot: find the swap slot number for an aobj/pageidx
    *
    * => object must be locked by caller
    */
   
   int
   uao_find_swslot(struct uvm_object *uobj, int pageidx)
   {
           struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
           struct uao_swhash_elt *elt;
   
           KASSERT(UVM_OBJ_IS_AOBJ(uobj));
   
           /*
            * 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)) {
                   elt = uao_find_swhash_elt(aobj, pageidx, false);
                   return elt ? UAO_SWHASH_ELT_PAGESLOT(elt, pageidx) : 0;
           }
   
           /*
            * 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
    * => we return the old slot number, or -1 if we failed to allocate
    *    memory to record the new slot number
    */
   
   int
   uao_set_swslot(struct uvm_object *uobj, int pageidx, int slot)
   {
           struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
           struct uao_swhash_elt *elt;
           int oldslot;
           UVMHIST_FUNC(__func__);
           UVMHIST_CALLARGS(pdhist, "aobj %#jx pageidx %jd slot %jd",
               (uintptr_t)aobj, pageidx, slot, 0);
   
           KASSERT(rw_write_held(uobj->vmobjlock) || uobj->uo_refs == 0);
           KASSERT(UVM_OBJ_IS_AOBJ(uobj));
   
           /*
            * if noswap flag is set, then we can't set a non-zero slot.
            */
   
           if (aobj->u_flags & UAO_FLAG_NOSWAP) {
                   KASSERTMSG(slot == 0, "uao_set_swslot: no swap object");
                   return 0;
           }
   
           /*
            * are we using a hash table?  if so, add it in the hash.
            */
   
           if (UAO_USES_SWHASH(aobj)) {
   
                   /*
                    * Avoid allocating an entry just to free it again if
                    * the page had not swap slot in the first place, and
                    * we are freeing.
                    */
   
                   elt = uao_find_swhash_elt(aobj, pageidx, slot != 0);
                   if (elt == NULL) {
                           return slot ? -1 : 0;
                   }
   
                   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) {
                           if (oldslot == 0)
                                   elt->count++;
                   } else {
                           if (oldslot)
                                   elt->count--;
   
                           if (elt->count == 0) {
                                   LIST_REMOVE(elt, list);
                                   pool_put(&uao_swhash_elt_pool, elt);
                           }
                   }
           } else {
                   /* we are using an array */
                   oldslot = aobj->u_swslots[pageidx];
                   aobj->u_swslots[pageidx] = slot;
           }
           return oldslot;
   }
   
   #endif /* defined(VMSWAP) */
   
   /*
    * 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(struct uvm_aobj *aobj)
   {
           struct uvm_object *uobj = &aobj->u_obj;
   
           KASSERT(UVM_OBJ_IS_AOBJ(uobj));
           KASSERT(rw_write_held(uobj->vmobjlock));
           uao_dropswap_range(uobj, 0, 0);
           rw_exit(uobj->vmobjlock);
   
   #if defined(VMSWAP)
           if (UAO_USES_SWHASH(aobj)) {
   
                   /*
                    * free the hash table itself.
                    */
   
                   hashdone(aobj->u_swhash, HASH_LIST, aobj->u_swhashmask);
           } else {
   
                   /*
                    * free the array itself.
                    */
   
                   kmem_free(aobj->u_swslots, aobj->u_pages * sizeof(int));
           }
   #endif /* defined(VMSWAP) */
   
           /*
            * finally free the aobj itself
            */
   
           uvm_obj_destroy(uobj, true);
           kmem_free(aobj, sizeof(struct uvm_aobj));
   }
   
   /*
    * 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(voff_t size, int flags)
   {
           static struct uvm_aobj kernel_object_store;
           static krwlock_t bootstrap_kernel_object_lock;
           static int kobj_alloced __diagused = 0;
           pgoff_t pages = round_page((uint64_t)size) >> PAGE_SHIFT;
           struct uvm_aobj *aobj;
           int refs;
   
           /*
            * Allocate a new aobj, unless kernel object is requested.
            */
   
           if (flags & UAO_FLAG_KERNOBJ) {
                   KASSERT(!kobj_alloced);
                   aobj = &kernel_object_store;
                   aobj->u_pages = pages;
                   aobj->u_flags = UAO_FLAG_NOSWAP;
                   refs = UVM_OBJ_KERN;
                   kobj_alloced = UAO_FLAG_KERNOBJ;
           } else if (flags & UAO_FLAG_KERNSWAP) {
                   KASSERT(kobj_alloced == UAO_FLAG_KERNOBJ);
                   aobj = &kernel_object_store;
                   kobj_alloced = UAO_FLAG_KERNSWAP;
                   refs = 0xdeadbeaf; /* XXX: gcc */
           } else {
                   aobj = kmem_alloc(sizeof(struct uvm_aobj), KM_SLEEP);
                   aobj->u_pages = pages;
                   aobj->u_flags = 0;
                   refs = 1;
           }
   
           /*
            * no freelist by default
            */
   
           aobj->u_freelist = VM_NFREELIST;
   
           /*
            * 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.
            */
   
           const int kernswap = (flags & UAO_FLAG_KERNSWAP) != 0;
           if (flags == 0 || kernswap) {
   #if defined(VMSWAP)
   
                   /* allocate hash table or array depending on object size */
                   if (UAO_USES_SWHASH(aobj)) {
                           aobj->u_swhash = hashinit(UAO_SWHASH_BUCKETS(aobj),
                               HASH_LIST, true, &aobj->u_swhashmask);
                   } else {
                           aobj->u_swslots = kmem_zalloc(pages * sizeof(int),
                               KM_SLEEP);
                   }
   #endif /* defined(VMSWAP) */
   
                   /*
                    * Replace kernel_object's temporary static lock with
                    * a regular rw_obj.  We cannot use uvm_obj_setlock()
                    * because that would try to free the old lock.
                    */
   
                   if (kernswap) {
                           aobj->u_obj.vmobjlock = rw_obj_alloc();
                           rw_destroy(&bootstrap_kernel_object_lock);
                   }
                   if (flags) {
                           aobj->u_flags &= ~UAO_FLAG_NOSWAP; /* clear noswap */
                           return &aobj->u_obj;
                   }
           }
   
           /*
            * Initialise UVM object.
            */
   
           const bool kernobj = (flags & UAO_FLAG_KERNOBJ) != 0;
           uvm_obj_init(&aobj->u_obj, &aobj_pager, !kernobj, refs);
           if (__predict_false(kernobj)) {
                   /* Use a temporary static lock for kernel_object. */
                   rw_init(&bootstrap_kernel_object_lock);
                   uvm_obj_setlock(&aobj->u_obj, &bootstrap_kernel_object_lock);
           }
   
           /*
            * now that aobj is ready, add it to the global list
            */
   
           mutex_enter(&uao_list_lock);
           LIST_INSERT_HEAD(&uao_list, aobj, u_list);
           mutex_exit(&uao_list_lock);
           return(&aobj->u_obj);
   }
   
   /*
    * uao_set_pgfl: allocate pages only from the specified freelist.
    *
    * => must be called before any pages are allocated for the object.
    * => reset by setting it to VM_NFREELIST, meaning any freelist.
    */
   
   void
   uao_set_pgfl(struct uvm_object *uobj, int freelist)
   {
           struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
   
           KASSERTMSG((0 <= freelist), "invalid freelist %d", freelist);
           KASSERTMSG((freelist <= VM_NFREELIST), "invalid freelist %d",
               freelist);
   
           aobj->u_freelist = freelist;
   }
   
   /*
    * uao_pagealloc: allocate a page for aobj.
    */
   
   static inline struct vm_page *
   uao_pagealloc(struct uvm_object *uobj, voff_t offset, int flags)
   {
           struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
   
           if (__predict_true(aobj->u_freelist == VM_NFREELIST))
                   return uvm_pagealloc(uobj, offset, NULL, flags);
           else
                   return uvm_pagealloc_strat(uobj, offset, NULL, flags,
                       UVM_PGA_STRAT_ONLY, aobj->u_freelist);
   }
   
   /*
    * uao_init: set up aobj pager subsystem
    *
    * => called at boot time from uvm_pager_init()
    */
   
   void
   uao_init(void)
   {
           static int uao_initialized;
   
           if (uao_initialized)
                   return;
           uao_initialized = true;
           LIST_INIT(&uao_list);
           mutex_init(&uao_list_lock, MUTEX_DEFAULT, IPL_NONE);
           pool_init(&uao_swhash_elt_pool, sizeof(struct uao_swhash_elt),
               0, 0, 0, "uaoeltpl", NULL, IPL_VM);
   }
   
   /*
    * uao_reference: hold a reference to an anonymous UVM object.
    */
   void
   uao_reference(struct uvm_object *uobj)
   {
           /* Kernel object is persistent. */
           if (UVM_OBJ_IS_KERN_OBJECT(uobj)) {
                   return;
           }
           atomic_inc_uint(&uobj->uo_refs);
   }
   
   /*
    * uao_detach: drop a reference to an anonymous UVM object.
    */
   void
   uao_detach(struct uvm_object *uobj)
   {
           struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
           struct uvm_page_array a;
           struct vm_page *pg;
   
           UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
   
           /*
            * Detaching from kernel object is a NOP.
            */
   
           if (UVM_OBJ_IS_KERN_OBJECT(uobj))
                   return;
   
           /*
            * Drop the reference.  If it was the last one, destroy the object.
            */
   
           KASSERT(uobj->uo_refs > 0);
           UVMHIST_LOG(maphist,"  (uobj=%#jx)  ref=%jd",
               (uintptr_t)uobj, uobj->uo_refs, 0, 0);
   #ifndef __HAVE_ATOMIC_AS_MEMBAR
           membar_release();
   #endif
           if (atomic_dec_uint_nv(&uobj->uo_refs) > 0) {
                   UVMHIST_LOG(maphist, "<- done (rc>0)", 0,0,0,0);
                   return;
           }
   #ifndef __HAVE_ATOMIC_AS_MEMBAR
           membar_acquire();
   #endif
   
           /*
            * Remove the aobj from the global list.
            */
   
           mutex_enter(&uao_list_lock);
           LIST_REMOVE(aobj, u_list);
           mutex_exit(&uao_list_lock);
   
           /*
            * Free all the pages left in the aobj.  For each page, when the
            * page is no longer busy (and thus after any disk I/O that it is
            * involved in is complete), release any swap resources and free
            * the page itself.
            */
           uvm_page_array_init(&a, uobj, 0);
           rw_enter(uobj->vmobjlock, RW_WRITER);
           while ((pg = uvm_page_array_fill_and_peek(&a, 0, 0)) != NULL) {
                   uvm_page_array_advance(&a);
                   pmap_page_protect(pg, VM_PROT_NONE);
                   if (pg->flags & PG_BUSY) {
                           uvm_pagewait(pg, uobj->vmobjlock, "uao_det");
                           uvm_page_array_clear(&a);
                           rw_enter(uobj->vmobjlock, RW_WRITER);
                           continue;
                   }
                   uao_dropswap(&aobj->u_obj, pg->offset >> PAGE_SHIFT);
                   uvm_pagefree(pg);
           }
           uvm_page_array_fini(&a);
   
           /*
            * Finally, free the anonymous UVM object itself.
            */
   
           uao_free(aobj);
   }
   
   /*
    * uao_put: flush pages out of a uvm object
    *
    * => object should be locked by caller.  we may _unlock_ the object
    *      if (and only if) we need to clean a page (PGO_CLEANIT).
    *      XXXJRT Currently, however, we don't.  In the case of cleaning
    *      XXXJRT a page, we simply just deactivate it.  Should probably
    *      XXXJRT handle this better, in the future (although "flushing"
    *      XXXJRT anonymous memory isn't terribly important).
    * => if PGO_CLEANIT is not set, then we will neither unlock the object
    *      or block.
    * => if PGO_ALLPAGE is set, then all pages in the object are valid targets
    *      for flushing.
    * => we return 0 unless we encountered some sort of I/O error
    *      XXXJRT currently never happens, as we never directly initiate
    *      XXXJRT I/O
    */
   
   static int
   uao_put(struct uvm_object *uobj, voff_t start, voff_t stop, int flags)
   {
           struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
           struct uvm_page_array a;
           struct vm_page *pg;
           voff_t curoff;
           UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
   
           KASSERT(UVM_OBJ_IS_AOBJ(uobj));
           KASSERT(rw_write_held(uobj->vmobjlock));
   
           if (flags & PGO_ALLPAGES) {
                   start = 0;
                   stop = aobj->u_pages << PAGE_SHIFT;
           } else {
                   start = trunc_page(start);
                   if (stop == 0) {
                           stop = aobj->u_pages << PAGE_SHIFT;
                   } else {
                           stop = round_page(stop);
                   }
                   if (stop > (uint64_t)(aobj->u_pages << PAGE_SHIFT)) {
                           printf("uao_put: strange, got an out of range "
                               "flush %#jx > %#jx (fixed)\n",
                               (uintmax_t)stop,
                               (uintmax_t)(aobj->u_pages << PAGE_SHIFT));
                           stop = aobj->u_pages << PAGE_SHIFT;
                   }
           }
           UVMHIST_LOG(maphist,
               " flush start=%#jx, stop=%#jx, flags=%#jx",
               start, stop, flags, 0);
   
           /*
            * Don't need to do any work here if we're not freeing
            * or deactivating pages.
            */
   
           if ((flags & (PGO_DEACTIVATE|PGO_FREE)) == 0) {
                   rw_exit(uobj->vmobjlock);
                   return 0;
           }
   
           /* locked: uobj */
           uvm_page_array_init(&a, uobj, 0);
           curoff = start;
           while ((pg = uvm_page_array_fill_and_peek(&a, curoff, 0)) != NULL) {
                   if (pg->offset >= stop) {
                           break;
                   }
   
                   /*
                    * wait and try again if the page is busy.
                    */
   
                   if (pg->flags & PG_BUSY) {
                           uvm_pagewait(pg, uobj->vmobjlock, "uao_put");
                           uvm_page_array_clear(&a);
                           rw_enter(uobj->vmobjlock, RW_WRITER);
                           continue;
                   }
                   uvm_page_array_advance(&a);
                   curoff = pg->offset + PAGE_SIZE;
   
                   switch (flags & (PGO_CLEANIT|PGO_FREE|PGO_DEACTIVATE)) {
   
                   /*
                    * XXX In these first 3 cases, we always just
                    * XXX deactivate the page.  We may want to
                    * XXX handle the different cases more specifically
                    * XXX in the future.
                    */
   
                   case PGO_CLEANIT|PGO_FREE:
                   case PGO_CLEANIT|PGO_DEACTIVATE:
                   case PGO_DEACTIVATE:
    deactivate_it:
                           uvm_pagelock(pg);
                           uvm_pagedeactivate(pg);
                           uvm_pageunlock(pg);
                           break;
   
                   case PGO_FREE:
                           /*
                            * If there are multiple references to
                            * the object, just deactivate the page.
                            */
   
                           if (uobj->uo_refs > 1)
                                   goto deactivate_it;
   
                           /*
                            * free the swap slot and the page.
                            */
   
                           pmap_page_protect(pg, VM_PROT_NONE);
   
                           /*
                            * freeing swapslot here is not strictly necessary.
                            * however, leaving it here doesn't save much
                            * because we need to update swap accounting anyway.
                            */
   
                           uao_dropswap(uobj, pg->offset >> PAGE_SHIFT);
                           uvm_pagefree(pg);
                           break;
   
                   default:
                           panic("%s: impossible", __func__);
                   }
           }
           rw_exit(uobj->vmobjlock);
           uvm_page_array_fini(&a);
           return 0;
   }
   
   /*
    * 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.
    *
    * case 1 can be handled with PGO_LOCKED, cases 2 and 3 cannot.
    * so, if the "center" page hits case 2/3 then we will need to return EBUSY.
    *
    * => prefer map unlocked (not required)
    * => object must be locked!  we will _unlock_ it before starting any I/O.
    * => flags: 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(struct uvm_object *uobj, voff_t offset, struct vm_page **pps,
       int *npagesp, int centeridx, vm_prot_t access_type, int advice, int flags)
   {
           voff_t current_offset;
           struct vm_page *ptmp;
           int lcv, gotpages, maxpages, swslot, pageidx;
           bool overwrite = ((flags & PGO_OVERWRITE) != 0);
           struct uvm_page_array a;
   
           UVMHIST_FUNC(__func__);
           UVMHIST_CALLARGS(pdhist, "aobj=%#jx offset=%jd, flags=%#jx",
                       (uintptr_t)uobj, offset, flags,0);
   
           /*
            * the object must be locked.  it can only be a read lock when
            * processing a read fault with PGO_LOCKED.
            */
   
           KASSERT(UVM_OBJ_IS_AOBJ(uobj));
           KASSERT(rw_lock_held(uobj->vmobjlock));
           KASSERT(rw_write_held(uobj->vmobjlock) ||
              ((flags & PGO_LOCKED) != 0 && (access_type & VM_PROT_WRITE) == 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).
                    */
   
                   uvm_page_array_init(&a, uobj, 0);
                   gotpages = 0;   /* # of pages we got so far */
                   for (lcv = 0; lcv < maxpages; lcv++) {
                           ptmp = uvm_page_array_fill_and_peek(&a,
                               offset + (lcv << PAGE_SHIFT), maxpages);
                           if (ptmp == NULL) {
                                   break;
                           }
                           KASSERT(ptmp->offset >= offset);
                           lcv = (ptmp->offset - offset) >> PAGE_SHIFT;
                           if (lcv >= maxpages) {
                                   break;
                           }
                           uvm_page_array_advance(&a);
   
                           /*
                            * to be useful must get a non-busy page
                            */
   
                           if ((ptmp->flags & PG_BUSY) != 0) {
                                   continue;
                           }
   
                           /*
                            * useful page: plug it in our result array
                            */
   
                           KASSERT(uvm_pagegetdirty(ptmp) !=
                               UVM_PAGE_STATUS_CLEAN);
                           pps[lcv] = ptmp;
                           gotpages++;
                   }
                   uvm_page_array_fini(&a);
   
                   /*
                    * 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=%jd)",
                       (pps[centeridx] != NULL), 0,0,0);
                   *npagesp = gotpages;
                   return pps[centeridx] != NULL ? 0 : EBUSY;
           }
   
           /*
            * step 2: get non-resident or busy pages.
            * object is locked.   data structures are unlocked.
            */
   
           if ((flags & PGO_SYNCIO) == 0) {
                   goto done;
           }
   
           uvm_page_array_init(&a, uobj, 0);
           for (lcv = 0, current_offset = offset ; lcv < maxpages ;) {
   
                   /*
                    * 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].   we are
                    * ready to move on to the next page.
                    */
   
                   ptmp = uvm_page_array_fill_and_peek(&a, current_offset,
                       maxpages - lcv);
   
                   if (ptmp != NULL && ptmp->offset == current_offset) {
                           /* page is there, see if we need to wait on it */
                           if ((ptmp->flags & PG_BUSY) != 0) {
                                   UVMHIST_LOG(pdhist,
                                       "sleeping, ptmp->flags %#jx\n",
                                       ptmp->flags,0,0,0);
                                   uvm_pagewait(ptmp, uobj->vmobjlock, "uao_get");
                                   rw_enter(uobj->vmobjlock, RW_WRITER);
                                   uvm_page_array_clear(&a);
                                   continue;
                           }
   
                           /*
                            * if we get here then the page is resident and
                            * unbusy.  we busy it now (so we own it).  if
                            * overwriting, mark the page dirty up front as
                            * it will be zapped via an unmanaged mapping.
                            */
   
                           KASSERT(uvm_pagegetdirty(ptmp) !=
                               UVM_PAGE_STATUS_CLEAN);
                           if (overwrite) {
                                   uvm_pagemarkdirty(ptmp, UVM_PAGE_STATUS_DIRTY);
                           }
                           /* we own it, caller must un-busy */
                           ptmp->flags |= PG_BUSY;
                           UVM_PAGE_OWN(ptmp, "uao_get2");
                           pps[lcv++] = ptmp;
                           current_offset += PAGE_SIZE;
                           uvm_page_array_advance(&a);
                           continue;
                   } else {
                           KASSERT(ptmp == NULL || ptmp->offset > current_offset);
                   }
   
                   /*
                    * not resident.  allocate a new busy/fake/clean page in the
                    * object.  if it's in swap we need to do I/O to fill in the
                    * data, otherwise the page needs to be cleared: if it's not
                    * destined to be overwritten, then zero it here and now.
                    */
   
                   pageidx = current_offset >> PAGE_SHIFT;
                   swslot = uao_find_swslot(uobj, pageidx);
                   ptmp = uao_pagealloc(uobj, current_offset,
                       swslot != 0 || overwrite ? 0 : UVM_PGA_ZERO);
   
                   /* out of RAM? */
                   if (ptmp == NULL) {
                           rw_exit(uobj->vmobjlock);
                           UVMHIST_LOG(pdhist, "sleeping, ptmp == NULL",0,0,0,0);
                           uvm_wait("uao_getpage");
                           rw_enter(uobj->vmobjlock, RW_WRITER);
                           uvm_page_array_clear(&a);
                           continue;
                   }
   
                   /*
                    * if swslot == 0, page hasn't existed before and is zeroed.
                    * otherwise we have a "fake/busy/clean" page that we just
                    * allocated.  do the needed "i/o", reading from swap.
                    */
   
                   if (swslot != 0) {
   #if defined(VMSWAP)
                           int error;
   
                           UVMHIST_LOG(pdhist, "pagein from swslot %jd",
                                swslot, 0,0,0);
   
                           /*
                            * page in the swapped-out page.
                            * unlock object for i/o, relock when done.
                            */
   
                           uvm_page_array_clear(&a);
                           rw_exit(uobj->vmobjlock);
                           error = uvm_swap_get(ptmp, swslot, PGO_SYNCIO);
                           rw_enter(uobj->vmobjlock, RW_WRITER);
  
                          /*
                           * I/O done.  check for errors.
                           */
  
                          if (error != 0) {
                                  UVMHIST_LOG(pdhist, "<- done (error=%jd)",
                                      error,0,0,0);
  
                                  /*
                                   * remove the swap slot from the aobj
                                   * and mark the aobj as having no real slot.
                                   * don't free the swap slot, thus preventing
                                   * it from being used again.
                                   */
  
                                  swslot = uao_set_swslot(uobj, pageidx,
                                      SWSLOT_BAD);
                                  if (swslot > 0) {
                                          uvm_swap_markbad(swslot, 1);
                                  }
  
                                  uvm_pagefree(ptmp);
                                  rw_exit(uobj->vmobjlock);
                                  UVMHIST_LOG(pdhist, "<- done (error)",
                                      error,lcv,0,0);
                                  if (lcv != 0) {
                                          uvm_page_unbusy(pps, lcv);
                                  }
                                  memset(pps, 0, maxpages * sizeof(pps[0]));
                                  uvm_page_array_fini(&a);
                                  return error;
                          }
  #else /* defined(VMSWAP) */
                          panic("%s: pagein", __func__);
  #endif /* defined(VMSWAP) */
                  }
  
                  /*
                   * note that we will allow the page being writably-mapped
                   * (!PG_RDONLY) regardless of access_type.  if overwrite,
                   * the page can be modified through an unmanaged mapping
                   * so mark it dirty up front.
                   */
                  if (overwrite) {
                          uvm_pagemarkdirty(ptmp, UVM_PAGE_STATUS_DIRTY);
                  } else {
                          uvm_pagemarkdirty(ptmp, UVM_PAGE_STATUS_UNKNOWN);
                  }
  
                  /*
                   * 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
                   */
                  KASSERT(uvm_pagegetdirty(ptmp) != UVM_PAGE_STATUS_CLEAN);
                  KASSERT((ptmp->flags & PG_FAKE) != 0);
                  KASSERT(ptmp->offset == current_offset);
                  ptmp->flags &= ~PG_FAKE;
                  pps[lcv++] = ptmp;
                  current_offset += PAGE_SIZE;
          }
          uvm_page_array_fini(&a);
  
          /*
           * finally, unlock object and return.
           */
  
  done:
          rw_exit(uobj->vmobjlock);
          UVMHIST_LOG(pdhist, "<- done (OK)",0,0,0,0);
          return 0;
  }
  
  #if defined(VMSWAP)
  
  /*
   * uao_dropswap:  release any swap resources from this aobj page.
   *
   * => aobj must be locked or have a reference count of 0.
   */
  
  void
  uao_dropswap(struct uvm_object *uobj, int pageidx)
  {
          int slot;
  
          KASSERT(UVM_OBJ_IS_AOBJ(uobj));
  
          slot = uao_set_swslot(uobj, pageidx, 0);
          if (slot) {
                  uvm_swap_free(slot, 1);
          }
  }
  
  /*
   * page in every page in every aobj that is paged-out to a range of swslots.
   *
   * => nothing should be locked.
   * => returns true if pagein was aborted due to lack of memory.
   */
  
  bool
  uao_swap_off(int startslot, int endslot)
  {
          struct uvm_aobj *aobj;
  
          /*
           * Walk the list of all anonymous UVM objects.  Grab the first.
           */
          mutex_enter(&uao_list_lock);
          if ((aobj = LIST_FIRST(&uao_list)) == NULL) {
                  mutex_exit(&uao_list_lock);
                  return false;
          }
          uao_reference(&aobj->u_obj);
  
          do {
                  struct uvm_aobj *nextaobj;
                  bool rv;
  
                  /*
                   * Prefetch the next object and immediately hold a reference
                   * on it, so neither the current nor the next entry could
                   * disappear while we are iterating.
                   */
                  if ((nextaobj = LIST_NEXT(aobj, u_list)) != NULL) {
                          uao_reference(&nextaobj->u_obj);
                  }
                  mutex_exit(&uao_list_lock);
  
                  /*
                   * Page in all pages in the swap slot range.
                   */
                  rw_enter(aobj->u_obj.vmobjlock, RW_WRITER);
                  rv = uao_pagein(aobj, startslot, endslot);
                  rw_exit(aobj->u_obj.vmobjlock);
  
                  /* Drop the reference of the current object. */
                  uao_detach(&aobj->u_obj);
                  if (rv) {
                          if (nextaobj) {
                                  uao_detach(&nextaobj->u_obj);
                          }
                          return rv;
                  }
  
                  aobj = nextaobj;
                  mutex_enter(&uao_list_lock);
          } while (aobj);
  
          mutex_exit(&uao_list_lock);
          return false;
  }
  
  /*
   * page in any pages from aobj in the given range.
   *
   * => aobj must be locked and is returned locked.
   * => returns true if pagein was aborted due to lack of memory.
   */
  static bool
  uao_pagein(struct uvm_aobj *aobj, int startslot, int endslot)
  {
          bool rv;
  
          if (UAO_USES_SWHASH(aobj)) {
                  struct uao_swhash_elt *elt;
                  int buck;
  
  restart:
                  for (buck = aobj->u_swhashmask; buck >= 0; buck--) {
                          for (elt = LIST_FIRST(&aobj->u_swhash[buck]);
                               elt != NULL;
                               elt = LIST_NEXT(elt, list)) {
                                  int i;
  
                                  for (i = 0; i < UAO_SWHASH_CLUSTER_SIZE; i++) {
                                          int slot = elt->slots[i];
  
                                          /*
                                           * if the slot isn't in range, skip it.
                                           */
  
                                          if (slot < startslot ||
                                              slot >= endslot) {
                                                  continue;
                                          }
  
                                          /*
                                           * process the page,
                                           * the start over on this object
                                           * since the swhash elt
                                           * may have been freed.
                                           */
  
                                          rv = uao_pagein_page(aobj,
                                            UAO_SWHASH_ELT_PAGEIDX_BASE(elt) + i);
                                          if (rv) {
                                                  return rv;
                                          }
                                          goto restart;
                                  }
                          }
                  }
          } else {
                  int i;
  
                  for (i = 0; i < aobj->u_pages; i++) {
                          int slot = aobj->u_swslots[i];
  
                          /*
                           * if the slot isn't in range, skip it
                           */
  
                          if (slot < startslot || slot >= endslot) {
                                  continue;
                          }
  
                          /*
                           * process the page.
                           */
  
                          rv = uao_pagein_page(aobj, i);
                          if (rv) {
                                  return rv;
                          }
                  }
          }
  
          return false;
  }
  
  /*
   * uao_pagein_page: page in a single page from an anonymous UVM object.
   *
   * => Returns true if pagein was aborted due to lack of memory.
   * => Object must be locked and is returned locked.
   */
  
  static bool
  uao_pagein_page(struct uvm_aobj *aobj, int pageidx)
  {
          struct uvm_object *uobj = &aobj->u_obj;
          struct vm_page *pg;
          int rv, npages;
  
          pg = NULL;
          npages = 1;
  
          KASSERT(rw_write_held(uobj->vmobjlock));
          rv = uao_get(uobj, (voff_t)pageidx << PAGE_SHIFT, &pg, &npages,
              0, VM_PROT_READ | VM_PROT_WRITE, 0, PGO_SYNCIO);
  
          /*
           * relock and finish up.
           */
  
          rw_enter(uobj->vmobjlock, RW_WRITER);
          switch (rv) {
          case 0:
                  break;
  
          case EIO:
          case ERESTART:
  
                  /*
                   * nothing more to do on errors.
                   * ERESTART can only mean that the anon was freed,
                   * so again there's nothing to do.
                   */
  
                  return false;
  
          default:
                  return true;
          }
  
          /*
           * ok, we've got the page now.
           * mark it as dirty, clear its swslot and un-busy it.
           */
          uao_dropswap(&aobj->u_obj, pageidx);
  
          /*
           * make sure it's on a page queue.
           */
          uvm_pagelock(pg);
          uvm_pageenqueue(pg);
          uvm_pagewakeup(pg);
          uvm_pageunlock(pg);
  
          pg->flags &= ~(PG_BUSY|PG_FAKE);
          uvm_pagemarkdirty(pg, UVM_PAGE_STATUS_DIRTY);
          UVM_PAGE_OWN(pg, NULL);
  
          return false;
  }
  
  /*
   * uao_dropswap_range: drop swapslots in the range.
   *
   * => aobj must be locked and is returned locked.
   * => start is inclusive.  end is exclusive.
   */
  
  void
  uao_dropswap_range(struct uvm_object *uobj, voff_t start, voff_t end)
  {
          struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
          int swpgonlydelta = 0;
  
          KASSERT(UVM_OBJ_IS_AOBJ(uobj));
          KASSERT(rw_write_held(uobj->vmobjlock));
  
          if (end == 0) {
                  end = INT64_MAX;
          }
  
          if (UAO_USES_SWHASH(aobj)) {
                  int i, hashbuckets = aobj->u_swhashmask + 1;
                  voff_t taghi;
                  voff_t taglo;
  
                  taglo = UAO_SWHASH_ELT_TAG(start);
                  taghi = UAO_SWHASH_ELT_TAG(end);
  
                  for (i = 0; i < hashbuckets; i++) {
                          struct uao_swhash_elt *elt, *next;
  
                          for (elt = LIST_FIRST(&aobj->u_swhash[i]);
                               elt != NULL;
                               elt = next) {
                                  int startidx, endidx;
                                  int j;
  
                                  next = LIST_NEXT(elt, list);
  
                                  if (elt->tag < taglo || taghi < elt->tag) {
                                          continue;
                                  }
  
                                  if (elt->tag == taglo) {
                                          startidx =
                                              UAO_SWHASH_ELT_PAGESLOT_IDX(start);
                                  } else {
                                          startidx = 0;
                                  }
  
                                  if (elt->tag == taghi) {
                                          endidx =
                                              UAO_SWHASH_ELT_PAGESLOT_IDX(end);
                                  } else {
                                          endidx = UAO_SWHASH_CLUSTER_SIZE;
                                  }
  
                                  for (j = startidx; j < endidx; j++) {
                                          int slot = elt->slots[j];
  
                                          KASSERT(uvm_pagelookup(&aobj->u_obj,
                                              (UAO_SWHASH_ELT_PAGEIDX_BASE(elt)
                                              + j) << PAGE_SHIFT) == NULL);
                                          if (slot > 0) {
                                                  uvm_swap_free(slot, 1);
                                                  swpgonlydelta++;
                                                  KASSERT(elt->count > 0);
                                                  elt->slots[j] = 0;
                                                  elt->count--;
                                          }
                                  }
  
                                  if (elt->count == 0) {
                                          LIST_REMOVE(elt, list);
                                          pool_put(&uao_swhash_elt_pool, elt);
                                  }
                          }
                  }
          } else {
                  int i;
  
                  if (aobj->u_pages < end) {
                          end = aobj->u_pages;
                  }
                  for (i = start; i < end; i++) {
                          int slot = aobj->u_swslots[i];
  
                          if (slot > 0) {
                                  uvm_swap_free(slot, 1);
                                  swpgonlydelta++;
                          }
                  }
          }
  
          /*
           * adjust the counter of pages only in swap for all
           * the swap slots we've freed.
           */
  
          if (swpgonlydelta > 0) {
                  KASSERT(uvmexp.swpgonly >= swpgonlydelta);
                  atomic_add_int(&uvmexp.swpgonly, -swpgonlydelta);
          }
  }
  
  #endif /* defined(VMSWAP) */

Cache object: c7eff6bbb0378a75f048502fc4445ac4