FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_page.h

     /*-
      * 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_page.h     8.2 (Berkeley) 12/13/93
     *
     *
     * 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.
     *
     * $FreeBSD$
     */
    
    /*
     *      Resident memory system definitions.
     */
    
    #ifndef _VM_PAGE_
    #define _VM_PAGE_
    
    #include <vm/pmap.h>
    #include <vm/_vm_phys.h>
    
    /*
     *      Management of resident (logical) pages.
     *
     *      A small structure is kept for each resident
     *      page, indexed by page number.  Each structure
     *      is an element of several collections:
     *
     *              A radix tree used to quickly
     *              perform object/offset lookups
     *
     *              A list of all pages for a given object,
     *              so they can be quickly deactivated at
     *              time of deallocation.
     *
     *              An ordered list of pages due for pageout.
     *
     *      In addition, the structure contains the object
     *      and offset to which this page belongs (for pageout),
     *      and sundry status bits.
     *
     *      In general, operations on this structure's mutable fields are
     *      synchronized using either one of or a combination of locks.  If a
     *      field is annotated with two of these locks then holding either is
     *      sufficient for read access but both are required for write access.
     *      The queue lock for a page depends on the value of its queue field and is
    *      described in detail below.
    *
    *      The following annotations are possible:
    *      (A) the field must be accessed using atomic(9) and may require
    *          additional synchronization.
    *      (B) the page busy lock.
    *      (C) the field is immutable.
    *      (F) the per-domain lock for the free queues.
    *      (M) Machine dependent, defined by pmap layer.
    *      (O) the object that the page belongs to.
    *      (Q) the page's queue lock.
    *
    *      The busy lock is an embedded reader-writer lock that protects the
    *      page's contents and identity (i.e., its <object, pindex> tuple) as
    *      well as certain valid/dirty modifications.  To avoid bloating the
    *      the page structure, the busy lock lacks some of the features available
    *      the kernel's general-purpose synchronization primitives.  As a result,
    *      busy lock ordering rules are not verified, lock recursion is not
    *      detected, and an attempt to xbusy a busy page or sbusy an xbusy page
    *      results will trigger a panic rather than causing the thread to block.
    *      vm_page_sleep_if_busy() can be used to sleep until the page's busy
    *      state changes, after which the caller must re-lookup the page and
    *      re-evaluate its state.  vm_page_busy_acquire() will block until
    *      the lock is acquired.
    *
    *      The valid field is protected by the page busy lock (B) and object
    *      lock (O).  Transitions from invalid to valid are generally done
    *      via I/O or zero filling and do not require the object lock.
    *      These must be protected with the busy lock to prevent page-in or
    *      creation races.  Page invalidation generally happens as a result
    *      of truncate or msync.  When invalidated, pages must not be present
    *      in pmap and must hold the object lock to prevent concurrent
    *      speculative read-only mappings that do not require busy.  I/O
    *      routines may check for validity without a lock if they are prepared
    *      to handle invalidation races with higher level locks (vnode) or are
    *      unconcerned with races so long as they hold a reference to prevent
    *      recycling.  When a valid bit is set while holding a shared busy
    *      lock (A) atomic operations are used to protect against concurrent
    *      modification.
    *
    *      In contrast, the synchronization of accesses to the page's
    *      dirty field is a mix of machine dependent (M) and busy (B).  In
    *      the machine-independent layer, the page busy must be held to
    *      operate on the field.  However, the pmap layer is permitted to
    *      set all bits within the field without holding that lock.  If the
    *      underlying architecture does not support atomic read-modify-write
    *      operations on the field's type, then the machine-independent
    *      layer uses a 32-bit atomic on the aligned 32-bit word that
    *      contains the dirty field.  In the machine-independent layer,
    *      the implementation of read-modify-write operations on the
    *      field is encapsulated in vm_page_clear_dirty_mask().  An
    *      exclusive busy lock combined with pmap_remove_{write/all}() is the
    *      only way to ensure a page can not become dirty.  I/O generally
    *      removes the page from pmap to ensure exclusive access and atomic
    *      writes.
    *
    *      The ref_count field tracks references to the page.  References that
    *      prevent the page from being reclaimable are called wirings and are
    *      counted in the low bits of ref_count.  The containing object's
    *      reference, if one exists, is counted using the VPRC_OBJREF bit in the
    *      ref_count field.  Additionally, the VPRC_BLOCKED bit is used to
    *      atomically check for wirings and prevent new wirings via
    *      pmap_extract_and_hold().  When a page belongs to an object, it may be
    *      wired only when the object is locked, or the page is busy, or by
    *      pmap_extract_and_hold().  As a result, if the object is locked and the
    *      page is not busy (or is exclusively busied by the current thread), and
    *      the page is unmapped, its wire count will not increase.  The ref_count
    *      field is updated using atomic operations in most cases, except when it
    *      is known that no other references to the page exist, such as in the page
    *      allocator.  A page may be present in the page queues, or even actively
    *      scanned by the page daemon, without an explicitly counted referenced.
    *      The page daemon must therefore handle the possibility of a concurrent
    *      free of the page.
    *
    *      The queue state of a page consists of the queue and act_count fields of
    *      its atomically updated state, and the subset of atomic flags specified
    *      by PGA_QUEUE_STATE_MASK.  The queue field contains the page's page queue
    *      index, or PQ_NONE if it does not belong to a page queue.  To modify the
    *      queue field, the page queue lock corresponding to the old value must be
    *      held, unless that value is PQ_NONE, in which case the queue index must
    *      be updated using an atomic RMW operation.  There is one exception to
    *      this rule: the page daemon may transition the queue field from
    *      PQ_INACTIVE to PQ_NONE immediately prior to freeing the page during an
    *      inactive queue scan.  At that point the page is already dequeued and no
    *      other references to that vm_page structure can exist.  The PGA_ENQUEUED
    *      flag, when set, indicates that the page structure is physically inserted
    *      into the queue corresponding to the page's queue index, and may only be
    *      set or cleared with the corresponding page queue lock held.
    *
    *      To avoid contention on page queue locks, page queue operations (enqueue,
    *      dequeue, requeue) are batched using fixed-size per-CPU queues.  A
    *      deferred operation is requested by setting one of the flags in
    *      PGA_QUEUE_OP_MASK and inserting an entry into a batch queue.  When a
    *      queue is full, an attempt to insert a new entry will lock the page
    *      queues and trigger processing of the pending entries.  The
    *      type-stability of vm_page structures is crucial to this scheme since the
    *      processing of entries in a given batch queue may be deferred
    *      indefinitely.  In particular, a page may be freed with pending batch
    *      queue entries.  The page queue operation flags must be set using atomic
    *      RWM operations.
    */
   
   #if PAGE_SIZE == 4096
   #define VM_PAGE_BITS_ALL 0xffu
   typedef uint8_t vm_page_bits_t;
   #elif PAGE_SIZE == 8192
   #define VM_PAGE_BITS_ALL 0xffffu
   typedef uint16_t vm_page_bits_t;
   #elif PAGE_SIZE == 16384
   #define VM_PAGE_BITS_ALL 0xffffffffu
   typedef uint32_t vm_page_bits_t;
   #elif PAGE_SIZE == 32768
   #define VM_PAGE_BITS_ALL 0xfffffffffffffffflu
   typedef uint64_t vm_page_bits_t;
   #endif
   
   typedef union vm_page_astate {
           struct {
                   uint16_t flags;
                   uint8_t queue;
                   uint8_t act_count;
           };
           uint32_t _bits;
   } vm_page_astate_t;
   
   struct vm_page {
           union {
                   TAILQ_ENTRY(vm_page) q; /* page queue or free list (Q) */
                   struct {
                           SLIST_ENTRY(vm_page) ss; /* private slists */
                   } s;
                   struct {
                           u_long p;
                           u_long v;
                   } memguard;
                   struct {
                           void *slab;
                           void *zone;
                   } uma;
           } plinks;
           TAILQ_ENTRY(vm_page) listq;     /* pages in same object (O) */
           vm_object_t object;             /* which object am I in (O) */
           vm_pindex_t pindex;             /* offset into object (O,P) */
           vm_paddr_t phys_addr;           /* physical address of page (C) */
           struct md_page md;              /* machine dependent stuff */
           u_int ref_count;                /* page references (A) */
           u_int busy_lock;                /* busy owners lock (A) */
           union vm_page_astate a;         /* state accessed atomically (A) */
           uint8_t order;                  /* index of the buddy queue (F) */
           uint8_t pool;                   /* vm_phys freepool index (F) */
           uint8_t flags;                  /* page PG_* flags (P) */
           uint8_t oflags;                 /* page VPO_* flags (O) */
           int8_t psind;                   /* pagesizes[] index (O) */
           int8_t segind;                  /* vm_phys segment index (C) */
           /* NOTE that these must support one bit per DEV_BSIZE in a page */
           /* so, on normal X86 kernels, they must be at least 8 bits wide */
           vm_page_bits_t valid;           /* valid DEV_BSIZE chunk map (O,B) */
           vm_page_bits_t dirty;           /* dirty DEV_BSIZE chunk map (M,B) */
   };
   
   /*
    * Special bits used in the ref_count field.
    *
    * ref_count is normally used to count wirings that prevent the page from being
    * reclaimed, but also supports several special types of references that do not
    * prevent reclamation.  Accesses to the ref_count field must be atomic unless
    * the page is unallocated.
    *
    * VPRC_OBJREF is the reference held by the containing object.  It can set or
    * cleared only when the corresponding object's write lock is held.
    *
    * VPRC_BLOCKED is used to atomically block wirings via pmap lookups while
    * attempting to tear down all mappings of a given page.  The page busy lock and
    * object write lock must both be held in order to set or clear this bit.
    */
   #define VPRC_BLOCKED    0x40000000u     /* mappings are being removed */
   #define VPRC_OBJREF     0x80000000u     /* object reference, cleared with (O) */
   #define VPRC_WIRE_COUNT(c)      ((c) & ~(VPRC_BLOCKED | VPRC_OBJREF))
   #define VPRC_WIRE_COUNT_MAX     (~(VPRC_BLOCKED | VPRC_OBJREF))
   
   /*
    * Page flags stored in oflags:
    *
    * Access to these page flags is synchronized by the lock on the object
    * containing the page (O).
    *
    * Note: VPO_UNMANAGED (used by OBJT_DEVICE, OBJT_PHYS and OBJT_SG)
    *       indicates that the page is not under PV management but
    *       otherwise should be treated as a normal page.  Pages not
    *       under PV management cannot be paged out via the
    *       object/vm_page_t because there is no knowledge of their pte
    *       mappings, and such pages are also not on any PQ queue.
    *
    */
   #define VPO_KMEM_EXEC   0x01            /* kmem mapping allows execution */
   #define VPO_SWAPSLEEP   0x02            /* waiting for swap to finish */
   #define VPO_UNMANAGED   0x04            /* no PV management for page */
   #define VPO_SWAPINPROG  0x08            /* swap I/O in progress on page */
   
   /*
    * Busy page implementation details.
    * The algorithm is taken mostly by rwlock(9) and sx(9) locks implementation,
    * even if the support for owner identity is removed because of size
    * constraints.  Checks on lock recursion are then not possible, while the
    * lock assertions effectiveness is someway reduced.
    */
   #define VPB_BIT_SHARED          0x01
   #define VPB_BIT_EXCLUSIVE       0x02
   #define VPB_BIT_WAITERS         0x04
   #define VPB_BIT_FLAGMASK                                                \
           (VPB_BIT_SHARED | VPB_BIT_EXCLUSIVE | VPB_BIT_WAITERS)
   
   #define VPB_SHARERS_SHIFT       3
   #define VPB_SHARERS(x)                                                  \
           (((x) & ~VPB_BIT_FLAGMASK) >> VPB_SHARERS_SHIFT)
   #define VPB_SHARERS_WORD(x)     ((x) << VPB_SHARERS_SHIFT | VPB_BIT_SHARED)
   #define VPB_ONE_SHARER          (1 << VPB_SHARERS_SHIFT)
   
   #define VPB_SINGLE_EXCLUSIVE    VPB_BIT_EXCLUSIVE
   #ifdef INVARIANTS
   #define VPB_CURTHREAD_EXCLUSIVE                                         \
           (VPB_BIT_EXCLUSIVE | ((u_int)(uintptr_t)curthread & ~VPB_BIT_FLAGMASK))
   #else
   #define VPB_CURTHREAD_EXCLUSIVE VPB_SINGLE_EXCLUSIVE
   #endif
   
   #define VPB_UNBUSIED            VPB_SHARERS_WORD(0)
   
   /* Freed lock blocks both shared and exclusive. */
   #define VPB_FREED               (0xffffffff - VPB_BIT_SHARED)
   
   #define PQ_NONE         255
   #define PQ_INACTIVE     0
   #define PQ_ACTIVE       1
   #define PQ_LAUNDRY      2
   #define PQ_UNSWAPPABLE  3
   #define PQ_COUNT        4
   
   #ifndef VM_PAGE_HAVE_PGLIST
   TAILQ_HEAD(pglist, vm_page);
   #define VM_PAGE_HAVE_PGLIST
   #endif
   SLIST_HEAD(spglist, vm_page);
   
   #ifdef _KERNEL
   extern vm_page_t bogus_page;
   #endif  /* _KERNEL */
   
   extern struct mtx_padalign pa_lock[];
   
   #if defined(__arm__)
   #define PDRSHIFT        PDR_SHIFT
   #elif !defined(PDRSHIFT)
   #define PDRSHIFT        21
   #endif
   
   #define pa_index(pa)    ((pa) >> PDRSHIFT)
   #define PA_LOCKPTR(pa)  ((struct mtx *)(&pa_lock[pa_index(pa) % PA_LOCK_COUNT]))
   #define PA_LOCKOBJPTR(pa)       ((struct lock_object *)PA_LOCKPTR((pa)))
   #define PA_LOCK(pa)     mtx_lock(PA_LOCKPTR(pa))
   #define PA_TRYLOCK(pa)  mtx_trylock(PA_LOCKPTR(pa))
   #define PA_UNLOCK(pa)   mtx_unlock(PA_LOCKPTR(pa))
   #define PA_UNLOCK_COND(pa)                      \
           do {                                    \
                   if ((pa) != 0) {                \
                           PA_UNLOCK((pa));        \
                           (pa) = 0;               \
                   }                               \
           } while (0)
   
   #define PA_LOCK_ASSERT(pa, a)   mtx_assert(PA_LOCKPTR(pa), (a))
   
   #if defined(KLD_MODULE) && !defined(KLD_TIED)
   #define vm_page_lock(m)         vm_page_lock_KBI((m), LOCK_FILE, LOCK_LINE)
   #define vm_page_unlock(m)       vm_page_unlock_KBI((m), LOCK_FILE, LOCK_LINE)
   #define vm_page_trylock(m)      vm_page_trylock_KBI((m), LOCK_FILE, LOCK_LINE)
   #else   /* !KLD_MODULE */
   #define vm_page_lockptr(m)      (PA_LOCKPTR(VM_PAGE_TO_PHYS((m))))
   #define vm_page_lock(m)         mtx_lock(vm_page_lockptr((m)))
   #define vm_page_unlock(m)       mtx_unlock(vm_page_lockptr((m)))
   #define vm_page_trylock(m)      mtx_trylock(vm_page_lockptr((m)))
   #endif
   #if defined(INVARIANTS)
   #define vm_page_assert_locked(m)                \
       vm_page_assert_locked_KBI((m), __FILE__, __LINE__)
   #define vm_page_lock_assert(m, a)               \
       vm_page_lock_assert_KBI((m), (a), __FILE__, __LINE__)
   #else
   #define vm_page_assert_locked(m)
   #define vm_page_lock_assert(m, a)
   #endif
   
   /*
    * The vm_page's aflags are updated using atomic operations.  To set or clear
    * these flags, the functions vm_page_aflag_set() and vm_page_aflag_clear()
    * must be used.  Neither these flags nor these functions are part of the KBI.
    *
    * PGA_REFERENCED may be cleared only if the page is locked.  It is set by
    * both the MI and MD VM layers.  However, kernel loadable modules should not
    * directly set this flag.  They should call vm_page_reference() instead.
    *
    * PGA_WRITEABLE is set exclusively on managed pages by pmap_enter().
    * When it does so, the object must be locked, or the page must be
    * exclusive busied.  The MI VM layer must never access this flag
    * directly.  Instead, it should call pmap_page_is_write_mapped().
    *
    * PGA_EXECUTABLE may be set by pmap routines, and indicates that a page has
    * at least one executable mapping.  It is not consumed by the MI VM layer.
    *
    * PGA_NOSYNC must be set and cleared with the page busy lock held.
    *
    * PGA_ENQUEUED is set and cleared when a page is inserted into or removed
    * from a page queue, respectively.  It determines whether the plinks.q field
    * of the page is valid.  To set or clear this flag, page's "queue" field must
    * be a valid queue index, and the corresponding page queue lock must be held.
    *
    * PGA_DEQUEUE is set when the page is scheduled to be dequeued from a page
    * queue, and cleared when the dequeue request is processed.  A page may
    * have PGA_DEQUEUE set and PGA_ENQUEUED cleared, for instance if a dequeue
    * is requested after the page is scheduled to be enqueued but before it is
    * actually inserted into the page queue.
    *
    * PGA_REQUEUE is set when the page is scheduled to be enqueued or requeued
    * in its page queue.
    *
    * PGA_REQUEUE_HEAD is a special flag for enqueuing pages near the head of
    * the inactive queue, thus bypassing LRU.
    *
    * The PGA_DEQUEUE, PGA_REQUEUE and PGA_REQUEUE_HEAD flags must be set using an
    * atomic RMW operation to ensure that the "queue" field is a valid queue index,
    * and the corresponding page queue lock must be held when clearing any of the
    * flags.
    *
    * PGA_SWAP_FREE is used to defer freeing swap space to the pageout daemon
    * when the context that dirties the page does not have the object write lock
    * held.
    */
   #define PGA_WRITEABLE   0x0001          /* page may be mapped writeable */
   #define PGA_REFERENCED  0x0002          /* page has been referenced */
   #define PGA_EXECUTABLE  0x0004          /* page may be mapped executable */
   #define PGA_ENQUEUED    0x0008          /* page is enqueued in a page queue */
   #define PGA_DEQUEUE     0x0010          /* page is due to be dequeued */
   #define PGA_REQUEUE     0x0020          /* page is due to be requeued */
   #define PGA_REQUEUE_HEAD 0x0040         /* page requeue should bypass LRU */
   #define PGA_NOSYNC      0x0080          /* do not collect for syncer */
   #define PGA_SWAP_FREE   0x0100          /* page with swap space was dirtied */
   #define PGA_SWAP_SPACE  0x0200          /* page has allocated swap space */
   
   #define PGA_QUEUE_OP_MASK       (PGA_DEQUEUE | PGA_REQUEUE | PGA_REQUEUE_HEAD)
   #define PGA_QUEUE_STATE_MASK    (PGA_ENQUEUED | PGA_QUEUE_OP_MASK)
   
   /*
    * Page flags.  Updates to these flags are not synchronized, and thus they must
    * be set during page allocation or free to avoid races.
    *
    * The PG_PCPU_CACHE flag is set at allocation time if the page was
    * allocated from a per-CPU cache.  It is cleared the next time that the
    * page is allocated from the physical memory allocator.
    */
   #define PG_PCPU_CACHE   0x01            /* was allocated from per-CPU caches */
   #define PG_FICTITIOUS   0x02            /* physical page doesn't exist */
   #define PG_ZERO         0x04            /* page is zeroed */
   #define PG_MARKER       0x08            /* special queue marker page */
   #define PG_NODUMP       0x10            /* don't include this page in a dump */
   
   /*
    * Misc constants.
    */
   #define ACT_DECLINE             1
   #define ACT_ADVANCE             3
   #define ACT_INIT                5
   #define ACT_MAX                 64
   
   #ifdef _KERNEL
   
   #include <sys/systm.h>
   
   #include <machine/atomic.h>
   
   /*
    * Each pageable resident page falls into one of five lists:
    *
    *      free
    *              Available for allocation now.
    *
    *      inactive
    *              Low activity, candidates for reclamation.
    *              This list is approximately LRU ordered.
    *
    *      laundry
    *              This is the list of pages that should be
    *              paged out next.
    *
    *      unswappable
    *              Dirty anonymous pages that cannot be paged
    *              out because no swap device is configured.
    *
    *      active
    *              Pages that are "active", i.e., they have been
    *              recently referenced.
    *
    */
   
   extern vm_page_t vm_page_array;         /* First resident page in table */
   extern long vm_page_array_size;         /* number of vm_page_t's */
   extern long first_page;                 /* first physical page number */
   
   #define VM_PAGE_TO_PHYS(entry)  ((entry)->phys_addr)
   
   /*
    * PHYS_TO_VM_PAGE() returns the vm_page_t object that represents a memory
    * page to which the given physical address belongs. The correct vm_page_t
    * object is returned for addresses that are not page-aligned.
    */
   vm_page_t PHYS_TO_VM_PAGE(vm_paddr_t pa);
   
   /*
    * Page allocation parameters for vm_page for the functions
    * vm_page_alloc(), vm_page_grab(), vm_page_alloc_contig() and
    * vm_page_alloc_freelist().  Some functions support only a subset
    * of the flags, and ignore others, see the flags legend.
    *
    * The meaning of VM_ALLOC_ZERO differs slightly between the vm_page_alloc*()
    * and the vm_page_grab*() functions.  See these functions for details.
    *
    * Bits 0 - 1 define class.
    * Bits 2 - 15 dedicated for flags.
    * Legend:
    * (a) - vm_page_alloc() supports the flag.
    * (c) - vm_page_alloc_contig() supports the flag.
    * (f) - vm_page_alloc_freelist() supports the flag.
    * (g) - vm_page_grab() supports the flag.
    * (p) - vm_page_grab_pages() supports the flag.
    * Bits above 15 define the count of additional pages that the caller
    * intends to allocate.
    */
   #define VM_ALLOC_NORMAL         0
   #define VM_ALLOC_INTERRUPT      1
   #define VM_ALLOC_SYSTEM         2
   #define VM_ALLOC_CLASS_MASK     3
   #define VM_ALLOC_WAITOK         0x0008  /* (acf) Sleep and retry */
   #define VM_ALLOC_WAITFAIL       0x0010  /* (acf) Sleep and return error */
   #define VM_ALLOC_WIRED          0x0020  /* (acfgp) Allocate a wired page */
   #define VM_ALLOC_ZERO           0x0040  /* (acfgp) Allocate a prezeroed page */
   #define VM_ALLOC_NOOBJ          0x0100  /* (acg) No associated object */
   #define VM_ALLOC_NOBUSY         0x0200  /* (acgp) Do not excl busy the page */
   #define VM_ALLOC_NOCREAT        0x0400  /* (gp) Don't create a page */
   #define VM_ALLOC_IGN_SBUSY      0x1000  /* (gp) Ignore shared busy flag */
   #define VM_ALLOC_NODUMP         0x2000  /* (ag) don't include in dump */
   #define VM_ALLOC_SBUSY          0x4000  /* (acgp) Shared busy the page */
   #define VM_ALLOC_NOWAIT         0x8000  /* (acfgp) Do not sleep */
   #define VM_ALLOC_COUNT_SHIFT    16
   #define VM_ALLOC_COUNT(count)   ((count) << VM_ALLOC_COUNT_SHIFT)
   
   #ifdef M_NOWAIT
   static inline int
   malloc2vm_flags(int malloc_flags)
   {
           int pflags;
   
           KASSERT((malloc_flags & M_USE_RESERVE) == 0 ||
               (malloc_flags & M_NOWAIT) != 0,
               ("M_USE_RESERVE requires M_NOWAIT"));
           pflags = (malloc_flags & M_USE_RESERVE) != 0 ? VM_ALLOC_INTERRUPT :
               VM_ALLOC_SYSTEM;
           if ((malloc_flags & M_ZERO) != 0)
                   pflags |= VM_ALLOC_ZERO;
           if ((malloc_flags & M_NODUMP) != 0)
                   pflags |= VM_ALLOC_NODUMP;
           if ((malloc_flags & M_NOWAIT))
                   pflags |= VM_ALLOC_NOWAIT;
           if ((malloc_flags & M_WAITOK))
                   pflags |= VM_ALLOC_WAITOK;
           return (pflags);
   }
   #endif
   
   /*
    * Predicates supported by vm_page_ps_test():
    *
    *      PS_ALL_DIRTY is true only if the entire (super)page is dirty.
    *      However, it can be spuriously false when the (super)page has become
    *      dirty in the pmap but that information has not been propagated to the
    *      machine-independent layer.
    */
   #define PS_ALL_DIRTY    0x1
   #define PS_ALL_VALID    0x2
   #define PS_NONE_BUSY    0x4
   
   bool vm_page_busy_acquire(vm_page_t m, int allocflags);
   void vm_page_busy_downgrade(vm_page_t m);
   int vm_page_busy_tryupgrade(vm_page_t m);
   void vm_page_busy_sleep(vm_page_t m, const char *msg, bool nonshared);
   void vm_page_busy_sleep_unlocked(vm_object_t obj, vm_page_t m,
       vm_pindex_t pindex, const char *wmesg, bool nonshared);
   void vm_page_free(vm_page_t m);
   void vm_page_free_zero(vm_page_t m);
   
   void vm_page_activate (vm_page_t);
   void vm_page_advise(vm_page_t m, int advice);
   vm_page_t vm_page_alloc(vm_object_t, vm_pindex_t, int);
   vm_page_t vm_page_alloc_domain(vm_object_t, vm_pindex_t, int, int);
   vm_page_t vm_page_alloc_after(vm_object_t, vm_pindex_t, int, vm_page_t);
   vm_page_t vm_page_alloc_domain_after(vm_object_t, vm_pindex_t, int, int,
       vm_page_t);
   vm_page_t vm_page_alloc_contig(vm_object_t object, vm_pindex_t pindex, int req,
       u_long npages, vm_paddr_t low, vm_paddr_t high, u_long alignment,
       vm_paddr_t boundary, vm_memattr_t memattr);
   vm_page_t vm_page_alloc_contig_domain(vm_object_t object,
       vm_pindex_t pindex, int domain, int req, u_long npages, vm_paddr_t low,
       vm_paddr_t high, u_long alignment, vm_paddr_t boundary,
       vm_memattr_t memattr);
   vm_page_t vm_page_alloc_freelist(int, int);
   vm_page_t vm_page_alloc_freelist_domain(int, int, int);
   void vm_page_bits_set(vm_page_t m, vm_page_bits_t *bits, vm_page_bits_t set);
   bool vm_page_blacklist_add(vm_paddr_t pa, bool verbose);
   vm_page_t vm_page_grab(vm_object_t, vm_pindex_t, int);
   vm_page_t vm_page_grab_unlocked(vm_object_t, vm_pindex_t, int);
   int vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
       vm_page_t *ma, int count);
   int vm_page_grab_pages_unlocked(vm_object_t object, vm_pindex_t pindex,
       int allocflags, vm_page_t *ma, int count);
   int vm_page_grab_valid(vm_page_t *mp, vm_object_t object, vm_pindex_t pindex,
       int allocflags);
   int vm_page_grab_valid_unlocked(vm_page_t *mp, vm_object_t object,
       vm_pindex_t pindex, int allocflags);
   void vm_page_deactivate(vm_page_t);
   void vm_page_deactivate_noreuse(vm_page_t);
   void vm_page_dequeue(vm_page_t m);
   void vm_page_dequeue_deferred(vm_page_t m);
   vm_page_t vm_page_find_least(vm_object_t, vm_pindex_t);
   void vm_page_free_invalid(vm_page_t);
   vm_page_t vm_page_getfake(vm_paddr_t paddr, vm_memattr_t memattr);
   void vm_page_initfake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr);
   void vm_page_init_marker(vm_page_t marker, int queue, uint16_t aflags);
   int vm_page_insert (vm_page_t, vm_object_t, vm_pindex_t);
   void vm_page_invalid(vm_page_t m);
   void vm_page_launder(vm_page_t m);
   vm_page_t vm_page_lookup(vm_object_t, vm_pindex_t);
   vm_page_t vm_page_lookup_unlocked(vm_object_t, vm_pindex_t);
   vm_page_t vm_page_next(vm_page_t m);
   void vm_page_pqbatch_drain(void);
   void vm_page_pqbatch_submit(vm_page_t m, uint8_t queue);
   bool vm_page_pqstate_commit(vm_page_t m, vm_page_astate_t *old,
       vm_page_astate_t new);
   vm_page_t vm_page_prev(vm_page_t m);
   bool vm_page_ps_test(vm_page_t m, int flags, vm_page_t skip_m);
   void vm_page_putfake(vm_page_t m);
   void vm_page_readahead_finish(vm_page_t m);
   bool vm_page_reclaim_contig(int req, u_long npages, vm_paddr_t low,
       vm_paddr_t high, u_long alignment, vm_paddr_t boundary);
   bool vm_page_reclaim_contig_domain(int domain, int req, u_long npages,
       vm_paddr_t low, vm_paddr_t high, u_long alignment, vm_paddr_t boundary);
   void vm_page_reference(vm_page_t m);
   #define VPR_TRYFREE     0x01
   #define VPR_NOREUSE     0x02
   void vm_page_release(vm_page_t m, int flags);
   void vm_page_release_locked(vm_page_t m, int flags);
   vm_page_t vm_page_relookup(vm_object_t, vm_pindex_t);
   bool vm_page_remove(vm_page_t);
   bool vm_page_remove_xbusy(vm_page_t);
   int vm_page_rename(vm_page_t, vm_object_t, vm_pindex_t);
   void vm_page_replace(vm_page_t mnew, vm_object_t object,
       vm_pindex_t pindex, vm_page_t mold);
   int vm_page_sbusied(vm_page_t m);
   vm_page_t vm_page_scan_contig(u_long npages, vm_page_t m_start,
       vm_page_t m_end, u_long alignment, vm_paddr_t boundary, int options);
   vm_page_bits_t vm_page_set_dirty(vm_page_t m);
   void vm_page_set_valid_range(vm_page_t m, int base, int size);
   int vm_page_sleep_if_busy(vm_page_t m, const char *msg);
   int vm_page_sleep_if_xbusy(vm_page_t m, const char *msg);
   vm_offset_t vm_page_startup(vm_offset_t vaddr);
   void vm_page_sunbusy(vm_page_t m);
   bool vm_page_try_remove_all(vm_page_t m);
   bool vm_page_try_remove_write(vm_page_t m);
   int vm_page_trysbusy(vm_page_t m);
   int vm_page_tryxbusy(vm_page_t m);
   void vm_page_unhold_pages(vm_page_t *ma, int count);
   void vm_page_unswappable(vm_page_t m);
   void vm_page_unwire(vm_page_t m, uint8_t queue);
   bool vm_page_unwire_noq(vm_page_t m);
   void vm_page_updatefake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr);
   void vm_page_wire(vm_page_t);
   bool vm_page_wire_mapped(vm_page_t m);
   void vm_page_xunbusy_hard(vm_page_t m);
   void vm_page_xunbusy_hard_unchecked(vm_page_t m);
   void vm_page_set_validclean (vm_page_t, int, int);
   void vm_page_clear_dirty(vm_page_t, int, int);
   void vm_page_set_invalid(vm_page_t, int, int);
   void vm_page_valid(vm_page_t m);
   int vm_page_is_valid(vm_page_t, int, int);
   void vm_page_test_dirty(vm_page_t);
   vm_page_bits_t vm_page_bits(int base, int size);
   void vm_page_zero_invalid(vm_page_t m, boolean_t setvalid);
   void vm_page_free_pages_toq(struct spglist *free, bool update_wire_count);
   
   void vm_page_dirty_KBI(vm_page_t m);
   void vm_page_lock_KBI(vm_page_t m, const char *file, int line);
   void vm_page_unlock_KBI(vm_page_t m, const char *file, int line);
   int vm_page_trylock_KBI(vm_page_t m, const char *file, int line);
   #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
   void vm_page_assert_locked_KBI(vm_page_t m, const char *file, int line);
   void vm_page_lock_assert_KBI(vm_page_t m, int a, const char *file, int line);
   #endif
   
   #define vm_page_busy_fetch(m)   atomic_load_int(&(m)->busy_lock)
   
   #define vm_page_assert_busied(m)                                        \
           KASSERT(vm_page_busied(m),                                      \
               ("vm_page_assert_busied: page %p not busy @ %s:%d", \
               (m), __FILE__, __LINE__))
   
   #define vm_page_assert_sbusied(m)                                       \
           KASSERT(vm_page_sbusied(m),                                     \
               ("vm_page_assert_sbusied: page %p not shared busy @ %s:%d", \
               (m), __FILE__, __LINE__))
   
   #define vm_page_assert_unbusied(m)                                      \
           KASSERT((vm_page_busy_fetch(m) & ~VPB_BIT_WAITERS) !=           \
               VPB_CURTHREAD_EXCLUSIVE,                                    \
               ("vm_page_assert_xbusied: page %p busy_lock %#x owned"      \
               " by me @ %s:%d",                                           \
               (m), (m)->busy_lock, __FILE__, __LINE__));                  \
   
   #define vm_page_assert_xbusied_unchecked(m) do {                        \
           KASSERT(vm_page_xbusied(m),                                     \
               ("vm_page_assert_xbusied: page %p not exclusive busy @ %s:%d", \
               (m), __FILE__, __LINE__));                                  \
   } while (0)
   #define vm_page_assert_xbusied(m) do {                                  \
           vm_page_assert_xbusied_unchecked(m);                            \
           KASSERT((vm_page_busy_fetch(m) & ~VPB_BIT_WAITERS) ==           \
               VPB_CURTHREAD_EXCLUSIVE,                                    \
               ("vm_page_assert_xbusied: page %p busy_lock %#x not owned"  \
               " by me @ %s:%d",                                           \
               (m), (m)->busy_lock, __FILE__, __LINE__));                  \
   } while (0)
   
   #define vm_page_busied(m)                                               \
           (vm_page_busy_fetch(m) != VPB_UNBUSIED)
   
   #define vm_page_sbusy(m) do {                                           \
           if (!vm_page_trysbusy(m))                                       \
                   panic("%s: page %p failed shared busying", __func__,    \
                       (m));                                               \
   } while (0)
   
   #define vm_page_xbusied(m)                                              \
           ((vm_page_busy_fetch(m) & VPB_SINGLE_EXCLUSIVE) != 0)
   
   #define vm_page_busy_freed(m)                                           \
           (vm_page_busy_fetch(m) == VPB_FREED)
   
   #define vm_page_xbusy(m) do {                                           \
           if (!vm_page_tryxbusy(m))                                       \
                   panic("%s: page %p failed exclusive busying", __func__, \
                       (m));                                               \
   } while (0)
   
   /* Note: page m's lock must not be owned by the caller. */
   #define vm_page_xunbusy(m) do {                                         \
           if (!atomic_cmpset_rel_int(&(m)->busy_lock,                     \
               VPB_CURTHREAD_EXCLUSIVE, VPB_UNBUSIED))                     \
                   vm_page_xunbusy_hard(m);                                \
   } while (0)
   #define vm_page_xunbusy_unchecked(m) do {                               \
           if (!atomic_cmpset_rel_int(&(m)->busy_lock,                     \
               VPB_CURTHREAD_EXCLUSIVE, VPB_UNBUSIED))                     \
                   vm_page_xunbusy_hard_unchecked(m);                      \
   } while (0)
   
   #ifdef INVARIANTS
   void vm_page_object_busy_assert(vm_page_t m);
   #define VM_PAGE_OBJECT_BUSY_ASSERT(m)   vm_page_object_busy_assert(m)
   void vm_page_assert_pga_writeable(vm_page_t m, uint16_t bits);
   #define VM_PAGE_ASSERT_PGA_WRITEABLE(m, bits)                           \
           vm_page_assert_pga_writeable(m, bits)
   /*
    * Claim ownership of a page's xbusy state.  In non-INVARIANTS kernels this
    * operation is a no-op since ownership is not tracked.  In particular
    * this macro does not provide any synchronization with the previous owner.
    */
   #define vm_page_xbusy_claim(m) do {                                     \
           u_int _busy_lock;                                               \
                                                                           \
           vm_page_assert_xbusied_unchecked((m));                          \
           do {                                                            \
                   _busy_lock = vm_page_busy_fetch(m);                     \
           } while (!atomic_cmpset_int(&(m)->busy_lock, _busy_lock,        \
               (_busy_lock & VPB_BIT_FLAGMASK) | VPB_CURTHREAD_EXCLUSIVE)); \
   } while (0)
   #else
   #define VM_PAGE_OBJECT_BUSY_ASSERT(m)   (void)0
   #define VM_PAGE_ASSERT_PGA_WRITEABLE(m, bits)   (void)0
   #define vm_page_xbusy_claim(m)
   #endif
   
   #if BYTE_ORDER == BIG_ENDIAN
   #define VM_PAGE_AFLAG_SHIFT     16
   #else
   #define VM_PAGE_AFLAG_SHIFT     0
   #endif
   
   /*
    *      Load a snapshot of a page's 32-bit atomic state.
    */
   static inline vm_page_astate_t
   vm_page_astate_load(vm_page_t m)
   {
           vm_page_astate_t a;
   
           a._bits = atomic_load_32(&m->a._bits);
           return (a);
   }
   
   /*
    *      Atomically compare and set a page's atomic state.
    */
   static inline bool
   vm_page_astate_fcmpset(vm_page_t m, vm_page_astate_t *old, vm_page_astate_t new)
   {
   
           KASSERT(new.queue == PQ_INACTIVE || (new.flags & PGA_REQUEUE_HEAD) == 0,
               ("%s: invalid head requeue request for page %p", __func__, m));
           KASSERT((new.flags & PGA_ENQUEUED) == 0 || new.queue != PQ_NONE,
               ("%s: setting PGA_ENQUEUED with PQ_NONE in page %p", __func__, m));
           KASSERT(new._bits != old->_bits,
               ("%s: bits are unchanged", __func__));
   
           return (atomic_fcmpset_32(&m->a._bits, &old->_bits, new._bits) != 0);
   }
   
   /*
    *      Clear the given bits in the specified page.
    */
   static inline void
   vm_page_aflag_clear(vm_page_t m, uint16_t bits)
   {
           uint32_t *addr, val;
   
           /*
            * Access the whole 32-bit word containing the aflags field with an
            * atomic update.  Parallel non-atomic updates to the other fields
            * within this word are handled properly by the atomic update.
            */
           addr = (void *)&m->a;
           val = bits << VM_PAGE_AFLAG_SHIFT;
           atomic_clear_32(addr, val);
   }
   
   /*
    *      Set the given bits in the specified page.
    */
   static inline void
   vm_page_aflag_set(vm_page_t m, uint16_t bits)
   {
           uint32_t *addr, val;
   
           VM_PAGE_ASSERT_PGA_WRITEABLE(m, bits);
   
           /*
            * Access the whole 32-bit word containing the aflags field with an
            * atomic update.  Parallel non-atomic updates to the other fields
            * within this word are handled properly by the atomic update.
            */
           addr = (void *)&m->a;
           val = bits << VM_PAGE_AFLAG_SHIFT;
           atomic_set_32(addr, val);
   }
   
   /*
    *      vm_page_dirty:
    *
    *      Set all bits in the page's dirty field.
    *
    *      The object containing the specified page must be locked if the
    *      call is made from the machine-independent layer.
    *
    *      See vm_page_clear_dirty_mask().
    */
   static __inline void
   vm_page_dirty(vm_page_t m)
   {
   
           /* Use vm_page_dirty_KBI() under INVARIANTS to save memory. */
   #if (defined(KLD_MODULE) && !defined(KLD_TIED)) || defined(INVARIANTS)
           vm_page_dirty_KBI(m);
   #else
           m->dirty = VM_PAGE_BITS_ALL;
   #endif
   }
   
   /*
    *      vm_page_undirty:
    *
    *      Set page to not be dirty.  Note: does not clear pmap modify bits
    */
   static __inline void
   vm_page_undirty(vm_page_t m)
   {
   
           VM_PAGE_OBJECT_BUSY_ASSERT(m);
           m->dirty = 0;
   }
   
   static inline uint8_t
   _vm_page_queue(vm_page_astate_t as)
   {
   
           if ((as.flags & PGA_DEQUEUE) != 0)
                   return (PQ_NONE);
           return (as.queue);
   }
   
   /*
    *      vm_page_queue:
    *
    *      Return the index of the queue containing m.
    */
   static inline uint8_t
   vm_page_queue(vm_page_t m)
   {
   
           return (_vm_page_queue(vm_page_astate_load(m)));
   }
   
   static inline bool
   vm_page_active(vm_page_t m)
   {
   
           return (vm_page_queue(m) == PQ_ACTIVE);
   }
   
   static inline bool
   vm_page_inactive(vm_page_t m)
   {
   
           return (vm_page_queue(m) == PQ_INACTIVE);
   }
   
   static inline bool
   vm_page_in_laundry(vm_page_t m)
   {
           uint8_t queue;
   
           queue = vm_page_queue(m);
           return (queue == PQ_LAUNDRY || queue == PQ_UNSWAPPABLE);
   }
   
   /*
    *      vm_page_drop:
    *
    *      Release a reference to a page and return the old reference count.
    */
   static inline u_int
   vm_page_drop(vm_page_t m, u_int val)
   {
           u_int old;
   
           /*
            * Synchronize with vm_page_free_prep(): ensure that all updates to the
            * page structure are visible before it is freed.
            */
           atomic_thread_fence_rel();
           old = atomic_fetchadd_int(&m->ref_count, -val);
           KASSERT(old != VPRC_BLOCKED,
               ("vm_page_drop: page %p has an invalid refcount value", m));
           return (old);
   }
   
   /*
    *      vm_page_wired:
    *
    *      Perform a racy check to determine whether a reference prevents the page
    *      from being reclaimable.  If the page's object is locked, and the page is
    *      unmapped and exclusively busied by the current thread, no new wirings
    *      may be created.
    */
   static inline bool
   vm_page_wired(vm_page_t m)
   {
   
           return (VPRC_WIRE_COUNT(m->ref_count) > 0);
   }
   
   static inline bool
   vm_page_all_valid(vm_page_t m)
   {
   
           return (m->valid == VM_PAGE_BITS_ALL);
   }
   
   static inline bool
   vm_page_none_valid(vm_page_t m)
   {
   
           return (m->valid == 0);
   }
   
   static inline int
  vm_page_domain(vm_page_t m)
  {
  #ifdef NUMA
          int domn, segind;
  
          segind = m->segind;
          KASSERT(segind < vm_phys_nsegs, ("segind %d m %p", segind, m));
          domn = vm_phys_segs[segind].domain;
          KASSERT(domn >= 0 && domn < vm_ndomains, ("domain %d m %p", domn, m));
          return (domn);
  #else
          return (0);
  #endif
  }
  
  #endif                          /* _KERNEL */
  #endif                          /* !_VM_PAGE_ */

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