The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/uvm/uvm_amap.h

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    1 /*      $NetBSD: uvm_amap.h,v 1.30 2006/06/25 08:03:46 yamt Exp $       */
    2 
    3 /*
    4  *
    5  * Copyright (c) 1997 Charles D. Cranor and Washington University.
    6  * All rights reserved.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 3. All advertising materials mentioning features or use of this software
   17  *    must display the following acknowledgement:
   18  *      This product includes software developed by Charles D. Cranor and
   19  *      Washington University.
   20  * 4. The name of the author may not be used to endorse or promote products
   21  *    derived from this software without specific prior written permission.
   22  *
   23  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   24  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   25  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   26  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   27  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   28  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   29  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   30  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   31  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   32  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   33  */
   34 
   35 #ifndef _UVM_UVM_AMAP_H_
   36 #define _UVM_UVM_AMAP_H_
   37 
   38 /*
   39  * uvm_amap.h: general amap interface and amap implementation-specific info
   40  */
   41 
   42 /*
   43  * an amap structure contains pointers to a set of anons that are
   44  * mapped together in virtual memory (an anon is a single page of
   45  * anonymous virtual memory -- see uvm_anon.h).  in uvm we hide the
   46  * details of the implementation of amaps behind a general amap
   47  * interface.  this allows us to change the amap implementation
   48  * without having to touch the rest of the code.  this file is divided
   49  * into two parts: the definition of the uvm amap interface and the
   50  * amap implementation-specific definitions.
   51  */
   52 
   53 #ifdef _KERNEL
   54 
   55 /*
   56  * part 1: amap interface
   57  */
   58 
   59 /*
   60  * forward definition of vm_amap structure.  only amap
   61  * implementation-specific code should directly access the fields of
   62  * this structure.
   63  */
   64 
   65 struct vm_amap;
   66 
   67 
   68 /*
   69  * prototypes for the amap interface
   70  */
   71 
   72 void            amap_add        /* add an anon to an amap */
   73                         (struct vm_aref *, vaddr_t,
   74                          struct vm_anon *, boolean_t);
   75 struct vm_amap  *amap_alloc     /* allocate a new amap */
   76                         (vaddr_t, vaddr_t, int);
   77 void            amap_copy       /* clear amap needs-copy flag */
   78                         (struct vm_map *, struct vm_map_entry *, int,
   79                          vaddr_t, vaddr_t);
   80 void            amap_cow_now    /* resolve all COW faults now */
   81                         (struct vm_map *, struct vm_map_entry *);
   82 int             amap_extend     /* make amap larger */
   83                         (struct vm_map_entry *, vsize_t, int);
   84 int             amap_flags      /* get amap's flags */
   85                         (struct vm_amap *);
   86 void            amap_free       /* free amap */
   87                         (struct vm_amap *);
   88 void            amap_lock       /* lock amap */
   89                         (struct vm_amap *);
   90 struct vm_anon  *amap_lookup    /* lookup an anon @ offset in amap */
   91                         (struct vm_aref *, vaddr_t);
   92 void            amap_lookups    /* lookup multiple anons */
   93                         (struct vm_aref *, vaddr_t,
   94                          struct vm_anon **, int);
   95 void            amap_ref        /* add a reference to an amap */
   96                         (struct vm_amap *, vaddr_t, vsize_t, int);
   97 int             amap_refs       /* get number of references of amap */
   98                         (struct vm_amap *);
   99 void            amap_share_protect /* protect pages in a shared amap */
  100                         (struct vm_map_entry *, vm_prot_t);
  101 void            amap_splitref   /* split reference to amap into two */
  102                         (struct vm_aref *, struct vm_aref *, vaddr_t);
  103 void            amap_unadd      /* remove an anon from an amap */
  104                         (struct vm_aref *, vaddr_t);
  105 void            amap_unlock     /* unlock amap */
  106                         (struct vm_amap *);
  107 void            amap_unref      /* drop reference to an amap */
  108                         (struct vm_amap *, vaddr_t, vsize_t, int);
  109 void            amap_wipeout    /* remove all anons from amap */
  110                         (struct vm_amap *);
  111 boolean_t       amap_swap_off
  112                         (int, int);
  113 
  114 /*
  115  * amap flag values
  116  */
  117 
  118 #define AMAP_SHARED     0x1     /* amap is shared */
  119 #define AMAP_REFALL     0x2     /* amap_ref: reference entire amap */
  120 #define AMAP_SWAPOFF    0x4     /* amap_swap_off() is in progress */
  121 
  122 /*
  123  * amap_copy flags
  124  */
  125 
  126 #define AMAP_COPY_NOWAIT        0x02    /* not allowed to sleep */
  127 #define AMAP_COPY_NOCHUNK       0x04    /* not allowed to chunk */
  128 #define AMAP_COPY_NOMERGE       0x08    /* not allowed to merge */
  129 
  130 /*
  131  * amap_extend flags
  132  */
  133 #define AMAP_EXTEND_BACKWARDS   0x00    /* add "size" to start of map */
  134 #define AMAP_EXTEND_FORWARDS    0x01    /* add "size" to end of map */
  135 #define AMAP_EXTEND_NOWAIT      0x02    /* not allowed to sleep */
  136 
  137 #endif /* _KERNEL */
  138 
  139 /**********************************************************************/
  140 
  141 /*
  142  * part 2: amap implementation-specific info
  143  */
  144 
  145 /*
  146  * we currently provide an array-based amap implementation.  in this
  147  * implementation we provide the option of tracking split references
  148  * so that we don't lose track of references during partial unmaps
  149  * ... this is enabled with the "UVM_AMAP_PPREF" define.
  150  */
  151 
  152 #define UVM_AMAP_PPREF          /* track partial references */
  153 
  154 /*
  155  * here is the definition of the vm_amap structure for this implementation.
  156  */
  157 
  158 struct vm_amap {
  159         struct simplelock am_l; /* simple lock [locks all vm_amap fields] */
  160         int am_ref;             /* reference count */
  161         int am_flags;           /* flags */
  162         int am_maxslot;         /* max # of slots allocated */
  163         int am_nslot;           /* # of slots currently in map ( <= maxslot) */
  164         int am_nused;           /* # of slots currently in use */
  165         int *am_slots;          /* contig array of active slots */
  166         int *am_bckptr;         /* back pointer array to am_slots */
  167         struct vm_anon **am_anon; /* array of anonymous pages */
  168 #ifdef UVM_AMAP_PPREF
  169         int *am_ppref;          /* per page reference count (if !NULL) */
  170 #endif
  171         LIST_ENTRY(vm_amap) am_list;
  172 };
  173 
  174 /*
  175  * note that am_slots, am_bckptr, and am_anon are arrays.   this allows
  176  * fast lookup of pages based on their virual address at the expense of
  177  * some extra memory.   in the future we should be smarter about memory
  178  * usage and fall back to a non-array based implementation on systems
  179  * that are short of memory (XXXCDC).
  180  *
  181  * the entries in the array are called slots... for example an amap that
  182  * covers four pages of virtual memory is said to have four slots.   here
  183  * is an example of the array usage for a four slot amap.   note that only
  184  * slots one and three have anons assigned to them.  "D/C" means that we
  185  * "don't care" about the value.
  186  *
  187  *            0     1      2     3
  188  * am_anon:   NULL, anon0, NULL, anon1          (actual pointers to anons)
  189  * am_bckptr: D/C,  1,     D/C,  0              (points to am_slots entry)
  190  *
  191  * am_slots:  3, 1, D/C, D/C                    (says slots 3 and 1 are in use)
  192  *
  193  * note that am_bckptr is D/C if the slot in am_anon is set to NULL.
  194  * to find the entry in am_slots for an anon, look at am_bckptr[slot],
  195  * thus the entry for slot 3 in am_slots[] is at am_slots[am_bckptr[3]].
  196  * in general, if am_anon[X] is non-NULL, then the following must be
  197  * true: am_slots[am_bckptr[X]] == X
  198  *
  199  * note that am_slots is always contig-packed.
  200  */
  201 
  202 /*
  203  * defines for handling of large sparce amaps:
  204  *
  205  * one of the problems of array-based amaps is that if you allocate a
  206  * large sparcely-used area of virtual memory you end up allocating
  207  * large arrays that, for the most part, don't get used.  this is a
  208  * problem for BSD in that the kernel likes to make these types of
  209  * allocations to "reserve" memory for possible future use.
  210  *
  211  * for example, the kernel allocates (reserves) a large chunk of user
  212  * VM for possible stack growth.  most of the time only a page or two
  213  * of this VM is actually used.  since the stack is anonymous memory
  214  * it makes sense for it to live in an amap, but if we allocated an
  215  * amap for the entire stack range we could end up wasting a large
  216  * amount of malloc'd KVM.
  217  *
  218  * for example, on the i386 at boot time we allocate two amaps for the stack
  219  * of /sbin/init:
  220  *  1. a 7680 slot amap at protection 0 (reserve space for stack)
  221  *  2. a 512 slot amap at protection 7 (top of stack)
  222  *
  223  * most of the array allocated for the amaps for this is never used.
  224  * the amap interface provides a way for us to avoid this problem by
  225  * allowing amap_copy() to break larger amaps up into smaller sized
  226  * chunks (controlled by the "canchunk" option).   we use this feature
  227  * to reduce our memory usage with the BSD stack management.  if we
  228  * are asked to create an amap with more than UVM_AMAP_LARGE slots in it,
  229  * we attempt to break it up into a UVM_AMAP_CHUNK sized amap if the
  230  * "canchunk" flag is set.
  231  *
  232  * so, in the i386 example, the 7680 slot area is never referenced so
  233  * nothing gets allocated (amap_copy is never called because the protection
  234  * is zero).   the 512 slot area for the top of the stack is referenced.
  235  * the chunking code breaks it up into 16 slot chunks (hopefully a single
  236  * 16 slot chunk is enough to handle the whole stack).
  237  */
  238 
  239 #define UVM_AMAP_LARGE  256     /* # of slots in "large" amap */
  240 #define UVM_AMAP_CHUNK  16      /* # of slots to chunk large amaps in */
  241 
  242 #ifdef _KERNEL
  243 
  244 /*
  245  * macros
  246  */
  247 
  248 /* AMAP_B2SLOT: convert byte offset to slot */
  249 #define AMAP_B2SLOT(S,B) {                                              \
  250         KASSERT(((B) & (PAGE_SIZE - 1)) == 0);                          \
  251         (S) = (B) >> PAGE_SHIFT;                                        \
  252 }
  253 
  254 /*
  255  * lock/unlock/refs/flags macros
  256  */
  257 
  258 #define amap_flags(AMAP)        ((AMAP)->am_flags)
  259 #define amap_lock(AMAP)         simple_lock(&(AMAP)->am_l)
  260 #define amap_lock_try(AMAP)     simple_lock_try(&(AMAP)->am_l)
  261 #define amap_refs(AMAP)         ((AMAP)->am_ref)
  262 #define amap_unlock(AMAP)       simple_unlock(&(AMAP)->am_l)
  263 
  264 /*
  265  * if we enable PPREF, then we have a couple of extra functions that
  266  * we need to prototype here...
  267  */
  268 
  269 #ifdef UVM_AMAP_PPREF
  270 
  271 #define PPREF_NONE ((int *) -1) /* not using ppref */
  272 
  273 void            amap_pp_adjref          /* adjust references */
  274                         (struct vm_amap *, int, vsize_t, int);
  275 void            amap_pp_establish       /* establish ppref */
  276                         (struct vm_amap *, vaddr_t);
  277 void            amap_wiperange          /* wipe part of an amap */
  278                         (struct vm_amap *, int, int);
  279 #endif  /* UVM_AMAP_PPREF */
  280 
  281 #endif /* _KERNEL */
  282 
  283 #endif /* _UVM_UVM_AMAP_H_ */

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