FreeBSD/Linux Kernel Cross Reference
sys/uvm/uvm_amap.h

     /*      $NetBSD: uvm_amap.h,v 1.34 2008/10/26 08:32:02 bjs Exp $        */
     
     /*
      *
      * Copyright (c) 1997 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.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by Charles D. Cranor and
     *      Washington University.
     * 4. The name of the author may not be used to endorse or promote products
     *    derived from this software without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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.
     */
    
    #ifndef _UVM_UVM_AMAP_H_
    #define _UVM_UVM_AMAP_H_
    
    /*
     * uvm_amap.h: general amap interface and amap implementation-specific info
     */
    
    /*
     * an amap structure contains pointers to a set of anons that are
     * mapped together in virtual memory (an anon is a single page of
     * anonymous virtual memory -- see uvm_anon.h).  in uvm we hide the
     * details of the implementation of amaps behind a general amap
     * interface.  this allows us to change the amap implementation
     * without having to touch the rest of the code.  this file is divided
     * into two parts: the definition of the uvm amap interface and the
     * amap implementation-specific definitions.
     */
    
    #ifdef _KERNEL
    
    /*
     * part 1: amap interface
     */
    
    void    uvm_amap_init(void);
    
    /*
     * forward definition of vm_amap structure.  only amap
     * implementation-specific code should directly access the fields of
     * this structure.
     */
    
    struct vm_amap;
    
    
    /*
     * prototypes for the amap interface
     */
    
    void            amap_add        /* add an anon to an amap */
                            (struct vm_aref *, vaddr_t,
                             struct vm_anon *, bool);
    struct vm_amap  *amap_alloc     /* allocate a new amap */
                            (vaddr_t, vaddr_t, int);
    void            amap_copy       /* clear amap needs-copy flag */
                            (struct vm_map *, struct vm_map_entry *, int,
                             vaddr_t, vaddr_t);
    void            amap_cow_now    /* resolve all COW faults now */
                            (struct vm_map *, struct vm_map_entry *);
    int             amap_extend     /* make amap larger */
                            (struct vm_map_entry *, vsize_t, int);
    int             amap_flags      /* get amap's flags */
                            (struct vm_amap *);
    void            amap_free       /* free amap */
                            (struct vm_amap *);
    void            amap_lock       /* lock amap */
                            (struct vm_amap *);
    struct vm_anon  *amap_lookup    /* lookup an anon @ offset in amap */
                            (struct vm_aref *, vaddr_t);
    void            amap_lookups    /* lookup multiple anons */
                            (struct vm_aref *, vaddr_t,
                             struct vm_anon **, int);
    void            amap_ref        /* add a reference to an amap */
                            (struct vm_amap *, vaddr_t, vsize_t, int);
    int             amap_refs       /* get number of references of amap */
                           (struct vm_amap *);
   void            amap_share_protect /* protect pages in a shared amap */
                           (struct vm_map_entry *, vm_prot_t);
   void            amap_splitref   /* split reference to amap into two */
                           (struct vm_aref *, struct vm_aref *, vaddr_t);
   void            amap_unadd      /* remove an anon from an amap */
                           (struct vm_aref *, vaddr_t);
   void            amap_unlock     /* unlock amap */
                           (struct vm_amap *);
   void            amap_unref      /* drop reference to an amap */
                           (struct vm_amap *, vaddr_t, vsize_t, bool);
   void            amap_wipeout    /* remove all anons from amap */
                           (struct vm_amap *);
   bool            amap_swap_off
                           (int, int);
   
   /*
    * amap flag values
    */
   
   #define AMAP_SHARED     0x1     /* amap is shared */
   #define AMAP_REFALL     0x2     /* amap_ref: reference entire amap */
   #define AMAP_SWAPOFF    0x4     /* amap_swap_off() is in progress */
   
   /*
    * amap_copy flags
    */
   
   #define AMAP_COPY_NOWAIT        0x02    /* not allowed to sleep */
   #define AMAP_COPY_NOCHUNK       0x04    /* not allowed to chunk */
   #define AMAP_COPY_NOMERGE       0x08    /* not allowed to merge */
   
   /*
    * amap_extend flags
    */
   #define AMAP_EXTEND_BACKWARDS   0x00    /* add "size" to start of map */
   #define AMAP_EXTEND_FORWARDS    0x01    /* add "size" to end of map */
   #define AMAP_EXTEND_NOWAIT      0x02    /* not allowed to sleep */
   
   #endif /* _KERNEL */
   
   /**********************************************************************/
   
   /*
    * part 2: amap implementation-specific info
    */
   
   /*
    * we currently provide an array-based amap implementation.  in this
    * implementation we provide the option of tracking split references
    * so that we don't lose track of references during partial unmaps
    * ... this is enabled with the "UVM_AMAP_PPREF" define.
    */
   
   #define UVM_AMAP_PPREF          /* track partial references */
   
   /*
    * here is the definition of the vm_amap structure for this implementation.
    */
   
   struct vm_amap {
           kmutex_t am_l;          /* lock [locks all vm_amap fields] */
           int am_ref;             /* reference count */
           int am_flags;           /* flags */
           int am_maxslot;         /* max # of slots allocated */
           int am_nslot;           /* # of slots currently in map ( <= maxslot) */
           int am_nused;           /* # of slots currently in use */
           int *am_slots;          /* contig array of active slots */
           int *am_bckptr;         /* back pointer array to am_slots */
           struct vm_anon **am_anon; /* array of anonymous pages */
   #ifdef UVM_AMAP_PPREF
           int *am_ppref;          /* per page reference count (if !NULL) */
   #endif
           LIST_ENTRY(vm_amap) am_list;
   };
   
   /*
    * note that am_slots, am_bckptr, and am_anon are arrays.   this allows
    * fast lookup of pages based on their virual address at the expense of
    * some extra memory.   in the future we should be smarter about memory
    * usage and fall back to a non-array based implementation on systems
    * that are short of memory (XXXCDC).
    *
    * the entries in the array are called slots... for example an amap that
    * covers four pages of virtual memory is said to have four slots.   here
    * is an example of the array usage for a four slot amap.   note that only
    * slots one and three have anons assigned to them.  "D/C" means that we
    * "don't care" about the value.
    *
    *            0     1      2     3
    * am_anon:   NULL, anon0, NULL, anon1          (actual pointers to anons)
    * am_bckptr: D/C,  1,     D/C,  0              (points to am_slots entry)
    *
    * am_slots:  3, 1, D/C, D/C                    (says slots 3 and 1 are in use)
    *
    * note that am_bckptr is D/C if the slot in am_anon is set to NULL.
    * to find the entry in am_slots for an anon, look at am_bckptr[slot],
    * thus the entry for slot 3 in am_slots[] is at am_slots[am_bckptr[3]].
    * in general, if am_anon[X] is non-NULL, then the following must be
    * true: am_slots[am_bckptr[X]] == X
    *
    * note that am_slots is always contig-packed.
    */
   
   /*
    * defines for handling of large, sparse amaps:
    *
    * one of the problems of array-based amaps is that if you allocate a
    * large, sparsely-used area of virtual memory you end up allocating
    * large arrays that, for the most part, don't get used.  this is a
    * problem for BSD in that the kernel likes to make these types of
    * allocations to "reserve" memory for possible future use.
    *
    * for example, the kernel allocates (reserves) a large chunk of user
    * VM for possible stack growth.  most of the time only a page or two
    * of this VM is actually used.  since the stack is anonymous memory
    * it makes sense for it to live in an amap, but if we allocated an
    * amap for the entire stack range we could end up wasting a large
    * amount of malloc'd KVM.
    *
    * for example, on the i386 at boot time we allocate two amaps for the stack
    * of /sbin/init:
    *  1. a 7680 slot amap at protection 0 (reserve space for stack)
    *  2. a 512 slot amap at protection 7 (top of stack)
    *
    * most of the array allocated for the amaps for this is never used.
    * the amap interface provides a way for us to avoid this problem by
    * allowing amap_copy() to break larger amaps up into smaller sized
    * chunks (controlled by the "canchunk" option).   we use this feature
    * to reduce our memory usage with the BSD stack management.  if we
    * are asked to create an amap with more than UVM_AMAP_LARGE slots in it,
    * we attempt to break it up into a UVM_AMAP_CHUNK sized amap if the
    * "canchunk" flag is set.
    *
    * so, in the i386 example, the 7680 slot area is never referenced so
    * nothing gets allocated (amap_copy is never called because the protection
    * is zero).   the 512 slot area for the top of the stack is referenced.
    * the chunking code breaks it up into 16 slot chunks (hopefully a single
    * 16 slot chunk is enough to handle the whole stack).
    */
   
   #define UVM_AMAP_LARGE  256     /* # of slots in "large" amap */
   #define UVM_AMAP_CHUNK  16      /* # of slots to chunk large amaps in */
   
   #ifdef _KERNEL
   
   /*
    * macros
    */
   
   /* AMAP_B2SLOT: convert byte offset to slot */
   #define AMAP_B2SLOT(S,B) {                                              \
           KASSERT(((B) & (PAGE_SIZE - 1)) == 0);                          \
           (S) = (B) >> PAGE_SHIFT;                                        \
   }
   
   /*
    * lock/unlock/refs/flags macros
    */
   
   #define amap_flags(AMAP)        ((AMAP)->am_flags)
   #define amap_lock(AMAP)         mutex_enter(&(AMAP)->am_l)
   #define amap_lock_try(AMAP)     mutex_tryenter(&(AMAP)->am_l)
   #define amap_refs(AMAP)         ((AMAP)->am_ref)
   #define amap_unlock(AMAP)       mutex_exit(&(AMAP)->am_l)
   
   /*
    * if we enable PPREF, then we have a couple of extra functions that
    * we need to prototype here...
    */
   
   #ifdef UVM_AMAP_PPREF
   
   #define PPREF_NONE ((int *) -1) /* not using ppref */
   
   void            amap_pp_adjref          /* adjust references */
                           (struct vm_amap *, int, vsize_t, int);
   void            amap_pp_establish       /* establish ppref */
                           (struct vm_amap *, vaddr_t);
   void            amap_wiperange          /* wipe part of an amap */
                           (struct vm_amap *, int, int);
   #endif  /* UVM_AMAP_PPREF */
   
   #endif /* _KERNEL */
   
   #endif /* _UVM_UVM_AMAP_H_ */

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