sys/uvm/uvm_amap.h

   1 /*      $NetBSD: uvm_amap.h,v 1.37 2011/06/12 03:36:02 rmind Exp $      */
   2
   3 /*
   4  * Copyright (c) 1997 Charles D. Cranor and Washington University.
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  19  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26  */
  27
  28 #ifndef _UVM_UVM_AMAP_H_
  29 #define _UVM_UVM_AMAP_H_
  30
  31 /*
  32  * uvm_amap.h: general amap interface and amap implementation-specific info
  33  */
  34
  35 /*
  36  * an amap structure contains pointers to a set of anons that are
  37  * mapped together in virtual memory (an anon is a single page of
  38  * anonymous virtual memory -- see uvm_anon.h).  in uvm we hide the
  39  * details of the implementation of amaps behind a general amap
  40  * interface.  this allows us to change the amap implementation
  41  * without having to touch the rest of the code.  this file is divided
  42  * into two parts: the definition of the uvm amap interface and the
  43  * amap implementation-specific definitions.
  44  */
  45
  46 #ifdef _KERNEL
  47
  48 /*
  49  * part 1: amap interface
  50  */
  51
  52 void    uvm_amap_init(void);
  53
  54 /*
  55  * forward definition of vm_amap structure.  only amap
  56  * implementation-specific code should directly access the fields of
  57  * this structure.
  58  */
  59
  60 struct vm_amap;
  61
  62
  63 /*
  64  * prototypes for the amap interface
  65  */
  66
  67 void            amap_add        /* add an anon to an amap */
  68                         (struct vm_aref *, vaddr_t,
  69                          struct vm_anon *, bool);
  70 struct vm_amap  *amap_alloc     /* allocate a new amap */
  71                         (vaddr_t, vaddr_t, int);
  72 void            amap_copy       /* clear amap needs-copy flag */
  73                         (struct vm_map *, struct vm_map_entry *, int,
  74                          vaddr_t, vaddr_t);
  75 void            amap_cow_now    /* resolve all COW faults now */
  76                         (struct vm_map *, struct vm_map_entry *);
  77 int             amap_extend     /* make amap larger */
  78                         (struct vm_map_entry *, vsize_t, int);
  79 int             amap_flags      /* get amap's flags */
  80                         (struct vm_amap *);
  81 void            amap_free       /* free amap */
  82                         (struct vm_amap *);
  83 void            amap_lock       /* lock amap */
  84                         (struct vm_amap *);
  85 struct vm_anon  *amap_lookup    /* lookup an anon @ offset in amap */
  86                         (struct vm_aref *, vaddr_t);
  87 void            amap_lookups    /* lookup multiple anons */
  88                         (struct vm_aref *, vaddr_t,
  89                          struct vm_anon **, int);
  90 void            amap_ref        /* add a reference to an amap */
  91                         (struct vm_amap *, vaddr_t, vsize_t, int);
  92 int             amap_refs       /* get number of references of amap */
  93                         (struct vm_amap *);
  94 void            amap_share_protect /* protect pages in a shared amap */
  95                         (struct vm_map_entry *, vm_prot_t);
  96 void            amap_splitref   /* split reference to amap into two */
  97                         (struct vm_aref *, struct vm_aref *, vaddr_t);
  98 void            amap_unadd      /* remove an anon from an amap */
  99                         (struct vm_aref *, vaddr_t);
 100 void            amap_unlock     /* unlock amap */
 101                         (struct vm_amap *);
 102 void            amap_unref      /* drop reference to an amap */
 103                         (struct vm_amap *, vaddr_t, vsize_t, bool);
 104 void            amap_wipeout    /* remove all anons from amap */
 105                         (struct vm_amap *);
 106 bool            amap_swap_off
 107                         (int, int);
 108
 109 /*
 110  * amap flag values
 111  */
 112
 113 #define AMAP_SHARED     0x1     /* amap is shared */
 114 #define AMAP_REFALL     0x2     /* amap_ref: reference entire amap */
 115 #define AMAP_SWAPOFF    0x4     /* amap_swap_off() is in progress */
 116
 117 /*
 118  * amap_copy flags
 119  */
 120
 121 #define AMAP_COPY_NOWAIT        0x02    /* not allowed to sleep */
 122 #define AMAP_COPY_NOCHUNK       0x04    /* not allowed to chunk */
 123 #define AMAP_COPY_NOMERGE       0x08    /* not allowed to merge */
 124
 125 /*
 126  * amap_extend flags
 127  */
 128 #define AMAP_EXTEND_BACKWARDS   0x00    /* add "size" to start of map */
 129 #define AMAP_EXTEND_FORWARDS    0x01    /* add "size" to end of map */
 130 #define AMAP_EXTEND_NOWAIT      0x02    /* not allowed to sleep */
 131
 132 #endif /* _KERNEL */
 133
 134 /**********************************************************************/
 135
 136 /*
 137  * part 2: amap implementation-specific info
 138  */
 139
 140 /*
 141  * we currently provide an array-based amap implementation.  in this
 142  * implementation we provide the option of tracking split references
 143  * so that we don't lose track of references during partial unmaps
 144  * ... this is enabled with the "UVM_AMAP_PPREF" define.
 145  */
 146
 147 #define UVM_AMAP_PPREF          /* track partial references */
 148
 149 /*
 150  * here is the definition of the vm_amap structure for this implementation.
 151  */
 152
 153 struct vm_amap {
 154         kmutex_t *am_lock;      /* lock [locks all vm_amap fields] */
 155         int am_ref;             /* reference count */
 156         int am_flags;           /* flags */
 157         int am_maxslot;         /* max # of slots allocated */
 158         int am_nslot;           /* # of slots currently in map ( <= maxslot) */
 159         int am_nused;           /* # of slots currently in use */
 160         int *am_slots;          /* contig array of active slots */
 161         int *am_bckptr;         /* back pointer array to am_slots */
 162         struct vm_anon **am_anon; /* array of anonymous pages */
 163 #ifdef UVM_AMAP_PPREF
 164         int *am_ppref;          /* per page reference count (if !NULL) */
 165 #endif
 166         LIST_ENTRY(vm_amap) am_list;
 167 };
 168
 169 /*
 170  * note that am_slots, am_bckptr, and am_anon are arrays.   this allows
 171  * fast lookup of pages based on their virual address at the expense of
 172  * some extra memory.   in the future we should be smarter about memory
 173  * usage and fall back to a non-array based implementation on systems
 174  * that are short of memory (XXXCDC).
 175  *
 176  * the entries in the array are called slots... for example an amap that
 177  * covers four pages of virtual memory is said to have four slots.   here
 178  * is an example of the array usage for a four slot amap.   note that only
 179  * slots one and three have anons assigned to them.  "D/C" means that we
 180  * "don't care" about the value.
 181  *
 182  *            0     1      2     3
 183  * am_anon:   NULL, anon0, NULL, anon1          (actual pointers to anons)
 184  * am_bckptr: D/C,  1,     D/C,  0              (points to am_slots entry)
 185  *
 186  * am_slots:  3, 1, D/C, D/C                    (says slots 3 and 1 are in use)
 187  *
 188  * note that am_bckptr is D/C if the slot in am_anon is set to NULL.
 189  * to find the entry in am_slots for an anon, look at am_bckptr[slot],
 190  * thus the entry for slot 3 in am_slots[] is at am_slots[am_bckptr[3]].
 191  * in general, if am_anon[X] is non-NULL, then the following must be
 192  * true: am_slots[am_bckptr[X]] == X
 193  *
 194  * note that am_slots is always contig-packed.
 195  */
 196
 197 /*
 198  * defines for handling of large, sparse amaps:
 199  *
 200  * one of the problems of array-based amaps is that if you allocate a
 201  * large, sparsely-used area of virtual memory you end up allocating
 202  * large arrays that, for the most part, don't get used.  this is a
 203  * problem for BSD in that the kernel likes to make these types of
 204  * allocations to "reserve" memory for possible future use.
 205  *
 206  * for example, the kernel allocates (reserves) a large chunk of user
 207  * VM for possible stack growth.  most of the time only a page or two
 208  * of this VM is actually used.  since the stack is anonymous memory
 209  * it makes sense for it to live in an amap, but if we allocated an
 210  * amap for the entire stack range we could end up wasting a large
 211  * amount of allocated KVM.
 212  *
 213  * for example, on the i386 at boot time we allocate two amaps for the stack
 214  * of /sbin/init:
 215  *  1. a 7680 slot amap at protection 0 (reserve space for stack)
 216  *  2. a 512 slot amap at protection 7 (top of stack)
 217  *
 218  * most of the array allocated for the amaps for this is never used.
 219  * the amap interface provides a way for us to avoid this problem by
 220  * allowing amap_copy() to break larger amaps up into smaller sized
 221  * chunks (controlled by the "canchunk" option).   we use this feature
 222  * to reduce our memory usage with the BSD stack management.  if we
 223  * are asked to create an amap with more than UVM_AMAP_LARGE slots in it,
 224  * we attempt to break it up into a UVM_AMAP_CHUNK sized amap if the
 225  * "canchunk" flag is set.
 226  *
 227  * so, in the i386 example, the 7680 slot area is never referenced so
 228  * nothing gets allocated (amap_copy is never called because the protection
 229  * is zero).   the 512 slot area for the top of the stack is referenced.
 230  * the chunking code breaks it up into 16 slot chunks (hopefully a single
 231  * 16 slot chunk is enough to handle the whole stack).
 232  */
 233
 234 #define UVM_AMAP_LARGE  256     /* # of slots in "large" amap */
 235 #define UVM_AMAP_CHUNK  16      /* # of slots to chunk large amaps in */
 236
 237 #ifdef _KERNEL
 238
 239 /*
 240  * macros
 241  */
 242
 243 /* AMAP_B2SLOT: convert byte offset to slot */
 244 #define AMAP_B2SLOT(S,B) {                                              \
 245         KASSERT(((B) & (PAGE_SIZE - 1)) == 0);                          \
 246         (S) = (B) >> PAGE_SHIFT;                                        \
 247 }
 248
 249 /*
 250  * lock/unlock/refs/flags macros
 251  */
 252
 253 #define amap_flags(AMAP)        ((AMAP)->am_flags)
 254 #define amap_lock(AMAP)         mutex_enter((AMAP)->am_lock)
 255 #define amap_lock_try(AMAP)     mutex_tryenter((AMAP)->am_lock)
 256 #define amap_refs(AMAP)         ((AMAP)->am_ref)
 257 #define amap_unlock(AMAP)       mutex_exit((AMAP)->am_lock)
 258
 259 /*
 260  * if we enable PPREF, then we have a couple of extra functions that
 261  * we need to prototype here...
 262  */
 263
 264 #ifdef UVM_AMAP_PPREF
 265
 266 #define PPREF_NONE ((int *) -1) /* not using ppref */
 267
 268 void            amap_pp_adjref          /* adjust references */
 269                         (struct vm_amap *, int, vsize_t, int,
 270                         struct vm_anon **);
 271 void            amap_pp_establish       /* establish ppref */
 272                         (struct vm_amap *, vaddr_t);
 273 void            amap_wiperange          /* wipe part of an amap */
 274                         (struct vm_amap *, int, int, struct vm_anon **);
 275 #endif  /* UVM_AMAP_PPREF */
 276
 277 #endif /* _KERNEL */
 278
 279 #endif /* _UVM_UVM_AMAP_H_ */