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 1.41 2020/03/20 19:08:54 ad 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         krwlock_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, OP)     rw_enter((AMAP)->am_lock, (OP))
  255 #define amap_lock_try(AMAP, OP) rw_tryenter((AMAP)->am_lock, (OP))
  256 #define amap_refs(AMAP)         ((AMAP)->am_ref)
  257 #define amap_unlock(AMAP)       rw_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 void            amap_pp_establish       /* establish ppref */
  271                         (struct vm_amap *, vaddr_t);
  272 void            amap_wiperange          /* wipe part of an amap */
  273                         (struct vm_amap *, int, int);
  274 #endif  /* UVM_AMAP_PPREF */
  275 
  276 #endif /* _KERNEL */
  277 
  278 #endif /* _UVM_UVM_AMAP_H_ */

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