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Annotation of XNU/osfmk/vm/vm_external.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
        !             3:  *
        !             4:  * @APPLE_LICENSE_HEADER_START@
        !             5:  * 
        !             6:  * The contents of this file constitute Original Code as defined in and
        !             7:  * are subject to the Apple Public Source License Version 1.1 (the
        !             8:  * "License").  You may not use this file except in compliance with the
        !             9:  * License.  Please obtain a copy of the License at
        !            10:  * http://www.apple.com/publicsource and read it before using this file.
        !            11:  * 
        !            12:  * This Original Code and all software distributed under the License are
        !            13:  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
        !            14:  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
        !            15:  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
        !            16:  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
        !            17:  * License for the specific language governing rights and limitations
        !            18:  * under the License.
        !            19:  * 
        !            20:  * @APPLE_LICENSE_HEADER_END@
        !            21:  */
        !            22: /*
        !            23:  * @OSF_COPYRIGHT@
        !            24:  */
        !            25: /* 
        !            26:  * Mach Operating System
        !            27:  * Copyright (c) 1991,1990,1989 Carnegie Mellon University
        !            28:  * All Rights Reserved.
        !            29:  * 
        !            30:  * Permission to use, copy, modify and distribute this software and its
        !            31:  * documentation is hereby granted, provided that both the copyright
        !            32:  * notice and this permission notice appear in all copies of the
        !            33:  * software, derivative works or modified versions, and any portions
        !            34:  * thereof, and that both notices appear in supporting documentation.
        !            35:  * 
        !            36:  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
        !            37:  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
        !            38:  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
        !            39:  * 
        !            40:  * Carnegie Mellon requests users of this software to return to
        !            41:  * 
        !            42:  *  Software Distribution Coordinator  or  [email protected]
        !            43:  *  School of Computer Science
        !            44:  *  Carnegie Mellon University
        !            45:  *  Pittsburgh PA 15213-3890
        !            46:  * 
        !            47:  * any improvements or extensions that they make and grant Carnegie Mellon
        !            48:  * the rights to redistribute these changes.
        !            49:  */
        !            50: /*
        !            51:  */
        !            52: 
        !            53: /*
        !            54:  *     This module maintains information about the presence of
        !            55:  *     pages not in memory.  Since an external memory object
        !            56:  *     must maintain a complete knowledge of its contents, this
        !            57:  *     information takes the form of hints.
        !            58:  */
        !            59: #include <string.h>    /* for memcpy()/memset() */
        !            60: 
        !            61: #include <mach/boolean.h>
        !            62: #include <vm/vm_external.h>
        !            63: #include <kern/kalloc.h>
        !            64: #include <mach/vm_param.h>
        !            65: #include <kern/assert.h>
        !            66: 
        !            67: /*
        !            68:  *     The implementation uses bit arrays to record whether
        !            69:  *     a page has been written to external storage.  For
        !            70:  *     convenience, these bit arrays come in various sizes.
        !            71:  *     For example, a map N bytes long can record:
        !            72:  *
        !            73:  *       16 bytes =   128 pages = (@ 4KB/page)    512KB
        !            74:  *     1024 bytes =  8192 pages = (@ 4KB/page)  32MB
        !            75:  *     4096 bytes = 32768 pages = (@ 4KB/page) 128MB
        !            76:  *
        !            77:  *     For a 32-bit machine with 4KB pages, the largest size
        !            78:  *     would be 128KB = 32 pages. Machines with a larger page
        !            79:  *     size are more efficient.
        !            80:  *
        !            81:  *     This subsystem must be very careful about memory allocation,
        !            82:  *     since vm_external_create() is almost always called with
        !            83:  *     vm_privilege set. The largest map to be allocated must be less
        !            84:  *     than or equal to a single page, and the kalloc subsystem must
        !            85:  *     never allocate more than a single page in response to a kalloc()
        !            86:  *     request. Also, vm_external_destroy() must not take any blocking
        !            87:  *     locks, since it is called with a vm_object lock held. This
        !            88:  *     implies that kfree() MUST be implemented in terms of zfree()
        !            89:  *     NOT kmem_free() for all request sizes that this subsystem uses.
        !            90:  *
        !            91:  *     For efficiency, this subsystem knows that the kalloc() subsystem
        !            92:  *     is implemented in terms of power-of-2 allocation, and that the
        !            93:  *     minimum allocation unit is KALLOC_MINSIZE
        !            94:  * 
        !            95:  *     XXXO
        !            96:  *     Should consider using existence_map to hold bits directly
        !            97:  *     when existence_size <= 4 bytes (i.e., 32 pages).
        !            98:  */
        !            99: 
        !           100: #define        SMALL_SIZE      KALLOC_MINSIZE
        !           101: #define        LARGE_SIZE      PAGE_SIZE
        !           102: 
        !           103: static vm_size_t power_of_2(vm_size_t size);
        !           104: 
        !           105: static vm_size_t
        !           106: power_of_2(vm_size_t size)
        !           107: {
        !           108:        vm_size_t power;
        !           109: 
        !           110:        power = 2 * SMALL_SIZE;
        !           111:        while (power < size) {
        !           112:                power <<= 1;
        !           113:        }
        !           114:        return(power);
        !           115: }
        !           116: 
        !           117: vm_external_map_t
        !           118: vm_external_create(
        !           119:        vm_offset_t     size)
        !           120: {
        !           121:        vm_size_t               bytes;
        !           122:        vm_external_map_t       result = VM_EXTERNAL_NULL;
        !           123: 
        !           124:        bytes = stob(size);
        !           125:        if (bytes <= SMALL_SIZE) {
        !           126:                if ((result = (vm_external_map_t)kalloc(SMALL_SIZE)) != NULL) {
        !           127:                        memset(result, 0, SMALL_SIZE);
        !           128:                }
        !           129:        } else if (bytes <= LARGE_SIZE) {
        !           130:                bytes = power_of_2(bytes);
        !           131: 
        !           132:                if ((result = (vm_external_map_t)kalloc(bytes)) != NULL) {
        !           133:                        memset(result, 0, bytes);
        !           134:                }
        !           135:        }
        !           136:        return(result);
        !           137: }
        !           138: 
        !           139: void
        !           140: vm_external_destroy(
        !           141:        vm_external_map_t       map,
        !           142:        vm_size_t               size)
        !           143: {
        !           144:        vm_size_t bytes;
        !           145: 
        !           146:        if (map == VM_EXTERNAL_NULL)
        !           147:                return;
        !           148: 
        !           149:        bytes = stob(size);
        !           150:        if (bytes <= SMALL_SIZE) {
        !           151:                bytes = SMALL_SIZE;
        !           152:        } else {
        !           153:                bytes = power_of_2(bytes);
        !           154:        }
        !           155:        kfree((vm_offset_t)map, bytes);
        !           156: }
        !           157: 
        !           158: /*
        !           159:  * Return the number of bytes needed for a vm_external_map given the
        !           160:  * size of the object to be mapped, i.e. the size of the map that was
        !           161:  * created by vm_external_create.
        !           162:  */
        !           163: vm_size_t
        !           164: vm_external_map_size(
        !           165:        vm_offset_t     size)
        !           166: {
        !           167:        vm_size_t       bytes;
        !           168: 
        !           169:        bytes = stob(size);
        !           170:        if (bytes != 0)
        !           171:                if (bytes <= SMALL_SIZE) {
        !           172:                        bytes = SMALL_SIZE;
        !           173:                } else {
        !           174:                        bytes = power_of_2(bytes);
        !           175:                }
        !           176:        return bytes;
        !           177: }
        !           178: 
        !           179: void
        !           180: vm_external_copy(
        !           181:        vm_external_map_t       old_map,
        !           182:        vm_size_t               old_size,
        !           183:        vm_external_map_t       new_map)
        !           184: {
        !           185:        /*
        !           186:         * Cannot copy non-existent maps
        !           187:         */
        !           188:        if ((old_map == VM_EXTERNAL_NULL) || (new_map == VM_EXTERNAL_NULL))
        !           189:                return;
        !           190: 
        !           191:        /*
        !           192:         * Copy old map to new
        !           193:         */
        !           194:        memcpy(new_map, old_map, stob(old_size));
        !           195: }
        !           196: 
        !           197: boolean_t
        !           198: vm_external_within(
        !           199:        vm_size_t       new_size,
        !           200:        vm_size_t       old_size)
        !           201: {
        !           202:        vm_size_t       new_bytes;
        !           203:        vm_size_t       old_bytes;
        !           204: 
        !           205:        assert(new_size >= old_size);
        !           206: 
        !           207:        /*
        !           208:         * "old_bytes" is calculated to be the actual amount of space
        !           209:         * allocated for a map of size "old_size".
        !           210:         */
        !           211:        old_bytes = stob(old_size);
        !           212:        if (old_bytes <= SMALL_SIZE) old_bytes = SMALL_SIZE;
        !           213:        else if (old_bytes <= LARGE_SIZE) old_bytes = power_of_2(old_bytes);
        !           214: 
        !           215:        /*
        !           216:         * "new_bytes" is the map size required to map the "new_size" object.
        !           217:         * Since the rounding algorithms are the same, we needn't actually
        !           218:         * round up new_bytes to get the correct answer
        !           219:         */
        !           220:        new_bytes = stob(new_size);
        !           221: 
        !           222:        return(new_bytes <= old_bytes);
        !           223: }
        !           224: 
        !           225: vm_external_state_t
        !           226: _vm_external_state_get(
        !           227:        vm_external_map_t       map,
        !           228:        vm_offset_t             offset)
        !           229: {
        !           230:        unsigned
        !           231:        int             bit, byte;
        !           232: 
        !           233:        assert (map != VM_EXTERNAL_NULL);
        !           234: 
        !           235:        bit = atop(offset);
        !           236:        byte = bit >> 3;
        !           237:        if (map[byte] & (1 << (bit & 07))) {
        !           238:                return VM_EXTERNAL_STATE_EXISTS;
        !           239:        } else {
        !           240:                return VM_EXTERNAL_STATE_ABSENT;
        !           241:        }
        !           242: }
        !           243: 
        !           244: void
        !           245: vm_external_state_set(
        !           246:        vm_external_map_t       map,
        !           247:        vm_offset_t             offset)
        !           248: {
        !           249:        unsigned
        !           250:        int             bit, byte;
        !           251: 
        !           252:        if (map == VM_EXTERNAL_NULL)
        !           253:                return;
        !           254: 
        !           255:        bit = atop(offset);
        !           256:        byte = bit >> 3;
        !           257:        map[byte] |= (1 << (bit & 07));
        !           258: }
        !           259: 
        !           260: void
        !           261: vm_external_state_clr(
        !           262:        vm_external_map_t       map,
        !           263:        vm_offset_t             offset)
        !           264: {
        !           265:        unsigned
        !           266:        int             bit, byte;
        !           267: 
        !           268:        if (map == VM_EXTERNAL_NULL)
        !           269:                return;
        !           270: 
        !           271:        bit = atop(offset);
        !           272:        byte = bit >> 3;
        !           273:        map[byte] &= ~(1 << (bit & 07));
        !           274: }
        !           275: 
        !           276: void   
        !           277: vm_external_module_initialize(void)
        !           278: {
        !           279: }

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