绋嬪簭15-7 linux/lib/malloc.c

  1 /*

  2  * malloc.c --- a general purpose kernel memory allocator for Linux.

  3  *

  4  * Written by Theodore Ts'o ([email protected]), 11/29/91

  5  *

  6  * This routine is written to be as fast as possible, so that it

  7  * can be called from the interrupt level.

  8  *

  9  * Limitations: maximum size of memory we can allocate using this routine

 10  *      is 4k, the size of a page in Linux.

 11  *

 12  * The general game plan is that each page (called a bucket) will only hold

 13  * objects of a given size.  When all of the object on a page are released,

 14  * the page can be returned to the general free pool.  When malloc() is

 15  * called, it looks for the smallest bucket size which will fulfill its

 16  * request, and allocate a piece of memory from that bucket pool.

 17  *

 18  * Each bucket has as its control block a bucket descriptor which keeps

 19  * track of how many objects are in use on that page, and the free list

 20  * for that page.  Like the buckets themselves, bucket descriptors are

 21  * stored on pages requested from get_free_page().  However, unlike buckets,

 22  * pages devoted to bucket descriptor pages are never released back to the

 23  * system.  Fortunately, a system should probably only need 1 or 2 bucket

 24  * descriptor pages, since a page can hold 256 bucket descriptors (which

 25  * corresponds to 1 megabyte worth of bucket pages.)  If the kernel is using

 26  * that much allocated memory, it's probably doing something wrong.  :-)

 27  *

 28  * Note: malloc() and free() both call get_free_page() and free_page()

 29  *      in sections of code where interrupts are turned off, to allow

 30  *      malloc() and free() to be safely called from an interrupt routine.

 31  *      (We will probably need this functionality when networking code,

 32  *      particularily things like NFS, is added to Linux.)  However, this

 33  *      presumes that get_free_page() and free_page() are interrupt-level

 34  *      safe, which they may not be once paging is added.  If this is the

 35  *      case, we will need to modify malloc() to keep a few unused pages

 36  *      "pre-allocated" so that it can safely draw upon those pages if

 37  *      it is called from an interrupt routine.

 38  *

 39  *      Another concern is that get_free_page() should not sleep; if it

 40  *      does, the code is carefully ordered so as to avoid any race

 41  *      conditions.  The catch is that if malloc() is called re-entrantly,

 42  *      there is a chance that unecessary pages will be grabbed from the

 43  *      system.  Except for the pages for the bucket descriptor page, the

 44  *      extra pages will eventually get released back to the system, though,

 45  *      so it isn't all that bad.

 46  */

 47

    /*

     *     malloc.c - Linux鐨勯�氱敤鍐呮牳鍐呭瓨鍒嗛厤鍑芥暟銆�

     *

     * 鐢�Theodore Ts'o缂栧埗 ([email protected]), 11/29/91

     *

     * 璇ュ嚱鏁拌��缂栧啓鎴愬敖鍙�鑳藉湴蹇�锛屼粠鑰屽彲浠ヤ粠涓�鏂�灞傝皟鐢ㄦ�ゅ嚱鏁般��

     *

     * 闄愬埗锛氫娇鐢ㄨ�ュ嚱鏁颁竴娆℃墍鑳藉垎閰嶇殑鏈�澶у唴瀛樻槸4k锛屼篃鍗�Linux涓�鍐呭瓨椤甸潰鐨勫ぇ灏忋��

     *

     * 缂栧啓璇ュ嚱鏁版墍閬靛惊鐨勪竴鑸�瑙勫垯鏄�姣忛〉(琚�绉颁负涓�涓�瀛樺偍妗�)浠呭垎閰嶆墍瑕佸�圭撼瀵硅薄鐨勫ぇ灏忋��

     * 褰撲竴椤典笂鐨勬墍鏈夊�硅薄閮介噴鏀惧悗锛岃�ラ〉灏卞彲浠ヨ繑鍥為�氱敤绌洪棽鍐呭瓨姹犮�傚綋malloc()琚�璋冪��

     * 鏃讹紝瀹冧細瀵绘壘婊¤冻瑕佹眰鐨勬渶灏忕殑瀛樺偍妗讹紝骞朵粠璇ュ瓨鍌ㄦ《涓�鍒嗛厤涓�鍧楀唴瀛樸��

     *

     * 姣忎釜瀛樺偍妗堕兘鏈変竴涓�浣滀负鍏舵帶鍒剁敤鐨勫瓨鍌ㄦ《鎻忚堪绗︼紝鍏朵腑璁板綍浜嗛〉闈�涓婃湁澶氬皯瀵硅薄姝ｈ��

     * 浣跨敤浠ュ強璇ラ〉涓婄┖闂插唴瀛樼殑鍒楄〃銆傚氨璞″瓨鍌ㄦ《鑷�韬�涓�鏍凤紝瀛樺偍妗舵弿杩扮�︿篃鏄�瀛樺偍鍦ㄤ娇鐢�

     * get_free_page()鐢宠�峰埌鐨勯〉闈�涓婄殑锛屼絾鏄�涓庡瓨鍌ㄦ《涓嶅悓鐨勬槸锛屾《鎻忚堪绗︽墍鍗犵敤鐨勯〉闈�

     * 灏嗕笉鍐嶄細閲婃斁缁欑郴缁熴�傚垢杩愮殑鏄�涓�涓�绯荤粺澶х害鍙�闇�瑕�1鍒�2椤电殑妗舵弿杩扮�﹂〉闈�锛屽洜涓轰竴

     * 涓�椤甸潰鍙�浠ュ瓨鏀�256涓�妗舵弿杩扮��(瀵瑰簲1MB鍐呭瓨鐨勫瓨鍌ㄦ《椤甸潰)銆傚�傛灉绯荤粺涓烘《鎻忚堪绗﹀��

     * 閰嶄簡璁稿�氬唴瀛橈紝閭ｄ箞鑲�瀹氱郴缁熶粈涔堝湴鏂瑰嚭浜嗛棶棰�J銆�

     *

     * 娉ㄦ剰锛�malloc()鍜�free()涓よ�呭叧闂�浜嗕腑鏂�鐨勪唬鐮侀儴鍒嗛兘璋冪敤浜�get_free_page()鍜�

     *       free_page()鍑芥暟锛屼互浣�malloc()鍜�free()鍙�浠ュ畨鍏ㄥ湴琚�浠庝腑鏂�绋嬪簭涓�璋冪敤

     *       (褰撶綉缁滀唬鐮侊紝灏ゅ叾鏄�NFS绛夎��鍔犲叆鍒�Linux涓�鏃跺氨鍙�鑳介渶瑕佽繖绉嶅姛鑳�)銆備絾鍓�

     *       鎻愭槸鍋囪��get_free_page()鍜�free_page()鏄�鍙�浠ュ畨鍏ㄥ湴鍦ㄤ腑鏂�绾х▼搴忎腑浣跨敤鐨勶��

     *       杩欏湪涓�鏃﹀姞鍏ヤ簡鍒嗛〉澶勭悊涔嬪悗灏卞彲鑳戒笉鏄�瀹夊叏鐨勩�傚�傛灉鐪熸槸杩欑�嶆儏鍐碉紝閭ｄ箞鎴戜滑

     *       灏遍渶瑕佷慨鏀�malloc()鏉モ�滈�勫厛鍒嗛厤鈥濆嚑椤典笉鐢ㄧ殑鍐呭瓨锛屽�傛��malloc()鍜�free()

     *       琚�浠庝腑鏂�绋嬪簭涓�璋冪敤鏃跺氨鍙�浠ュ畨鍏ㄥ湴浣跨敤杩欎簺椤甸潰銆�

     *

     *       鍙﹀�栭渶瑕佽�冭檻鍒扮殑鏄�get_free_page()涓嶅簲璇ョ潯鐪狅紱濡傛灉浼氱潯鐪犵殑璇濓紝鍒欎负浜嗛槻姝�

     *       浠讳綍绔炰簤鏉′欢锛屼唬鐮侀渶瑕佷粩缁嗗湴瀹夋帓椤哄簭銆� 鍏抽敭鍦ㄤ簬濡傛灉malloc()鏄�鍙�浠ラ噸鍏ュ湴

     *       琚�璋冪敤鐨勮瘽锛岄偅涔堝氨浼氬瓨鍦ㄤ笉蹇呰�佺殑椤甸潰琚�浠庣郴缁熶腑鍙栬蛋鐨勬満浼氥�傞櫎浜嗙敤浜庢《鎻忚堪

     *       绗︾殑椤甸潰锛岃繖浜涢�濆�栫殑椤甸潰鏈�缁堜細閲婃斁缁欑郴缁燂紝鎵�浠ュ苟涓嶆槸璞℃兂璞＄殑閭ｆ牱涓嶅ソ銆�

     */

 

 48 #include <linux/kernel.h> // 鍐呮牳澶存枃浠躲�傚惈鏈変竴浜涘唴鏍稿父鐢ㄥ嚱鏁扮殑鍘熷舰瀹氫箟銆�

 49 #include <linux/mm.h>     // 鍐呭瓨绠＄悊澶存枃浠躲�傚惈鏈夐〉闈㈠ぇ灏忓畾涔夊拰涓�浜涢〉闈㈤噴鏀惧嚱鏁板師鍨嬨��

 50 #include <asm/system.h>   // 绯荤粺澶存枃浠躲�傚畾涔変簡璁剧疆鎴栦慨鏀规弿杩扮��/涓�鏂�闂ㄧ瓑鐨勫祵鍏ュ紡姹囩紪瀹忋��

 51

    // 瀛樺偍妗舵弿杩扮�︾粨鏋勩��

 52 struct bucket_desc {    /* 16 bytes */

 53         void                    *page;          // 璇ユ《鎻忚堪绗﹀�瑰簲鐨勫唴瀛橀〉闈㈡寚閽堛��

 54         struct bucket_desc      *next;          // 涓嬩竴涓�鎻忚堪绗︽寚閽堛��

 55         void                    *freeptr;       // 鎸囧悜鏈�妗朵腑绌洪棽鍐呭瓨浣嶇疆鐨勬寚閽堛��

 56         unsigned short          refcnt;         // 寮曠敤璁℃暟銆�

 57         unsigned short          bucket_size;    // 鏈�鎻忚堪绗﹀�瑰簲瀛樺偍妗剁殑澶у皬銆�

 58 };

 59

    // 瀛樺偍妗舵弿杩扮�︾洰褰曠粨鏋勩��

 60 struct _bucket_dir {    /* 8 bytes */

 61         int                     size;      // 璇ュ瓨鍌ㄦ《鐨勫ぇ灏�(瀛楄妭鏁�)銆�

 62         struct bucket_desc      *chain;    // 璇ュ瓨鍌ㄦ《鐩�褰曢」鐨勬《鎻忚堪绗﹂摼琛ㄦ寚閽堛��

 63 };

 64

 65 /*

 66  * The following is the where we store a pointer to the first bucket

 67  * descriptor for a given size. 

 68  *

 69  * If it turns out that the Linux kernel allocates a lot of objects of a

 70  * specific size, then we may want to add that specific size to this list,

 71  * since that will allow the memory to be allocated more efficiently.

 72  * However, since an entire page must be dedicated to each specific size

 73  * on this list, some amount of temperance must be exercised here.

 74  *

 75  * Note that this list *must* be kept in order.

 76  */

    /*

     * 涓嬮潰鏄�鎴戜滑瀛樻斁绗�涓�涓�缁欏畾澶у皬瀛樺偍妗舵弿杩扮�︽寚閽堢殑鍦版柟銆�

     *

     * 濡傛灉Linux鍐呮牳鍒嗛厤浜嗚�稿�氭寚瀹氬ぇ灏忕殑瀵硅薄锛岄偅涔堟垜浠�灏卞笇鏈涘皢璇ユ寚瀹氱殑澶у皬鍔犲��

     * 璇ュ垪琛�(閾捐〃)涓�锛屽洜涓鸿繖鏍峰彲浠ヤ娇鍐呭瓨鐨勫垎閰嶆洿鏈夋晥銆備絾鏄�锛屽洜涓轰竴椤靛畬鏁村唴瀛橀〉闈�

     * 蹇呴』鐢ㄤ簬鍒楄〃涓�鎸囧畾澶у皬鐨勬墍鏈夊�硅薄锛屾墍浠ラ渶瑕佸仛鎬绘暟鏂归潰鐨勬祴璇曟搷浣溿��

     */

    // 瀛樺偍妗剁洰褰曞垪琛�(鏁扮粍)銆�

 77 struct _bucket_dir bucket_dir[] = {

 78         { 16,   (struct bucket_desc *) 0},    // 16瀛楄妭闀垮害鐨勫唴瀛樺潡銆�

 79         { 32,   (struct bucket_desc *) 0},    // 32瀛楄妭闀垮害鐨勫唴瀛樺潡銆�

 80         { 64,   (struct bucket_desc *) 0},    // 64瀛楄妭闀垮害鐨勫唴瀛樺潡銆�

 81         { 128,  (struct bucket_desc *) 0},    // 128瀛楄妭闀垮害鐨勫唴瀛樺潡銆�

 82         { 256,  (struct bucket_desc *) 0},    // 256瀛楄妭闀垮害鐨勫唴瀛樺潡銆�

 83         { 512,  (struct bucket_desc *) 0},    // 512瀛楄妭闀垮害鐨勫唴瀛樺潡銆�

 84         { 1024, (struct bucket_desc *) 0},    // 1024瀛楄妭闀垮害鐨勫唴瀛樺潡銆�

 85         { 2048, (struct bucket_desc *) 0},    // 2048瀛楄妭闀垮害鐨勫唴瀛樺潡銆�

 86         { 4096, (struct bucket_desc *) 0},    // 4096瀛楄妭(1椤�)鍐呭瓨銆�

 87         { 0,    (struct bucket_desc *) 0}};   /* End of list marker */

 88

 89 /*

 90  * This contains a linked list of free bucket descriptor blocks

 91  */

    /*

     * 涓嬮潰鏄�鍚�鏈夌┖闂叉《鎻忚堪绗﹀唴瀛樺潡鐨勯摼琛ㄣ��

     */

 92 struct bucket_desc *free_bucket_desc = (struct bucket_desc *) 0;

 93

 94 /*

 95  * This routine initializes a bucket description page.

 96  */

    /*

     * 涓嬮潰鐨勫瓙绋嬪簭鐢ㄤ簬鍒濆�嬪寲涓�椤垫《鎻忚堪绗﹂〉闈���

     */

    //// 鍒濆�嬪寲妗舵弿杩扮�︺��

    // 寤虹珛绌洪棽妗舵弿杩扮�﹂摼琛�锛屽苟璁�free_bucket_desc鎸囧悜绗�涓�涓�绌洪棽妗舵弿杩扮�︺��

 97 static inline void init_bucket_desc()

 98 {

 99         struct bucket_desc *bdesc, *first;

100         int     i;

101        

    // 鐢宠�蜂竴椤靛唴瀛橈紝鐢ㄤ簬瀛樻斁妗舵弿杩扮�︺�傚�傛灉澶辫触锛屽垯鏄剧ず鍒濆�嬪寲妗舵弿杩扮�︽椂鍐呭瓨涓嶅�熷嚭閿欎俊鎭�锛屾�绘満銆�

102         first = bdesc = (struct bucket_desc *) get_free_page();

103         if (!bdesc)

104                 panic("Out of memory in init_bucket_desc()");

    // 棣栧厛璁＄畻涓�椤靛唴瀛樹腑鍙�瀛樻斁鐨勬《鎻忚堪绗︽暟閲忥紝鐒跺悗瀵瑰叾寤虹珛鍗曞悜杩炴帴鎸囬拡銆�

105         for (i = PAGE_SIZE/sizeof(struct bucket_desc); i > 1; i--) {

106                 bdesc->next = bdesc+1;

107                 bdesc++;

108         }

109         /*

110          * This is done last, to avoid race conditions in case

111          * get_free_page() sleeps and this routine gets called again....

112          */

            /*

             * 杩欐槸鍦ㄦ渶鍚庡�勭悊鐨勶紝鐩�鐨勬槸涓轰簡閬垮厤鍦�get_free_page()鐫＄湢鏃惰�ュ瓙绋嬪簭鍙堣��

             * 璋冪敤鑰屽紩璧风殑绔炰簤鏉′欢銆�

             */

    // 灏嗙┖闂叉《鎻忚堪绗︽寚閽�free_bucket_desc鍔犲叆閾捐〃涓�銆�

113         bdesc->next = free_bucket_desc;

114         free_bucket_desc = first;

115 }

116

    //// 鍒嗛厤鍔ㄦ�佸唴瀛樺嚱鏁般��

    // 鍙傛暟锛�len - 璇锋眰鐨勫唴瀛樺潡闀垮害銆�

    // 杩斿洖锛氭寚鍚戣��鍒嗛厤鍐呭瓨鐨勬寚閽堛�傚�傛灉澶辫触鍒欒繑鍥�NULL銆�

117 void *malloc(unsigned int len)

118 {

119         struct _bucket_dir      *bdir;

120         struct bucket_desc      *bdesc;

121         void                    *retval;

122

123         /*

124          * First we search the bucket_dir to find the right bucket change

125          * for this request.

126          */

            /*

             * 棣栧厛鎴戜滑鎼滅储瀛樺偍妗剁洰褰�bucket_dir鏉ュ�绘壘閫傚悎璇锋眰鐨勬《澶у皬銆�

             */

    // 鎼滅储瀛樺偍妗剁洰褰曪紝瀵绘壘閫傚悎鐢宠�峰唴瀛樺潡澶у皬鐨勬《鎻忚堪绗﹂摼琛ㄣ�傚�傛灉鐩�褰曢」鐨勬《瀛楄妭鏁板ぇ浜庤�锋眰鐨勫瓧鑺�

    // 鏁帮紝灏辨壘鍒颁簡瀵瑰簲鐨勬《鐩�褰曢」銆�

127         for (bdir = bucket_dir; bdir->size; bdir++)

128                 if (bdir->size >= len)

129                         break;

    // 濡傛灉鎼滅储瀹屾暣涓�鐩�褰曢兘娌℃湁鎵惧埌鍚堥�傚ぇ灏忕殑鐩�褰曢」锛屽垯琛ㄦ槑鎵�璇锋眰鐨勫唴瀛樺潡澶у皬澶�澶э紝瓒呭嚭浜嗚��

    // 绋嬪簭鐨勫垎閰嶉檺鍒�(鏈�闀夸负1涓�椤甸��)銆備簬鏄�鏄剧ず鍑洪敊淇℃伅锛屾�绘満銆�

130         if (!bdir->size) {

131                 printk("malloc called with impossibly large argument (%d)\n",

132                         len);

133                 panic("malloc: bad arg");

134         }

135         /*

136          * Now we search for a bucket descriptor which has free space

137          */

            /*

             * 鐜板湪鎴戜滑鏉ユ悳绱㈠叿鏈夌┖闂茬┖闂寸殑妗舵弿杩扮�︺��

             */

138         cli();  /* Avoid race conditions */   /* 涓轰簡閬垮厤鍑虹幇绔炰簤鏉′欢锛岄�栧厛鍏充腑鏂� */

    // 鎼滅储瀵瑰簲妗剁洰褰曢」涓�鎻忚堪绗﹂摼琛�锛屾煡鎵惧叿鏈夌┖闂茬┖闂寸殑妗舵弿杩扮�︺�傚�傛灉妗舵弿杩扮�︾殑绌洪棽鍐呭瓨鎸囬拡

    // freeptr涓嶄负绌猴紝鍒欒〃绀烘壘鍒颁簡鐩稿簲鐨勬《鎻忚堪绗︺��

139         for (bdesc = bdir->chain; bdesc; bdesc = bdesc->next)

140                 if (bdesc->freeptr)

141                         break;

142         /*

143          * If we didn't find a bucket with free space, then we'll

144          * allocate a new one.

145          */

            /*

             * 濡傛灉娌℃湁鎵惧埌鍏锋湁绌洪棽绌洪棿鐨勬《鎻忚堪绗︼紝閭ｄ箞鎴戜滑灏辫�佹柊寤虹珛涓�涓�璇ョ洰褰曢」鐨勬弿杩扮�︺��

             */

146         if (!bdesc) {

147                 char            *cp;

148                 int             i;

149

    // 鑻�free_bucket_desc杩樹负绌烘椂锛岃〃绀虹��涓�娆¤皟鐢ㄨ�ョ▼搴忥紝鎴栬�呴摼琛ㄤ腑鎵�鏈夌┖妗舵弿杩扮�﹂兘宸茬敤瀹屻��

    // 姝ゆ椂灏遍渶瑕佺敵璇蜂竴涓�椤甸潰骞跺湪鍏朵笂寤虹珛骞跺垵濮嬪寲绌洪棽鎻忚堪绗﹂摼琛ㄣ��free_bucket_desc浼氭寚鍚戠��涓�

    // 涓�绌洪棽妗舵弿杩扮�︺��

150                 if (!free_bucket_desc) 

151                         init_bucket_desc();

    // 鍙�free_bucket_desc鎸囧悜鐨勭┖闂叉《鎻忚堪绗︼紝骞惰��free_bucket_desc鎸囧悜涓嬩竴涓�绌洪棽妗舵弿杩扮�︺��

152                 bdesc = free_bucket_desc;

153                 free_bucket_desc = bdesc->next;

    // 鍒濆�嬪寲璇ユ柊鐨勬《鎻忚堪绗︺�備护鍏跺紩鐢ㄦ暟閲忕瓑浜�0锛涙《鐨勫ぇ灏忕瓑浜庡�瑰簲妗剁洰褰曠殑澶у皬锛涚敵璇蜂竴鍐呭瓨椤甸潰锛�

    // 璁╂弿杩扮�︾殑椤甸潰鎸囬��page鎸囧悜璇ラ〉闈�锛涚┖闂插唴瀛樻寚閽堜篃鎸囧悜璇ラ〉寮�澶达紝鍥犱负姝ゆ椂鍏ㄤ负绌洪棽銆�

154                 bdesc->refcnt = 0;

155                 bdesc->bucket_size = bdir->size;

156                 bdesc->page = bdesc->freeptr = (void *) cp = get_free_page();

    // 濡傛灉鐢宠�峰唴瀛橀〉闈㈡搷浣滃け璐ワ紝鍒欐樉绀哄嚭閿欎俊鎭�锛屾�绘満銆�

157                 if (!cp)

158                         panic("Out of memory in kernel malloc()");

159                 /* Set up the chain of free objects */

                    /* 鍦ㄨ�ラ〉绌洪棽鍐呭瓨涓�寤虹珛绌洪棽瀵硅薄閾捐〃 */

    // 浠ヨ�ユ《鐩�褰曢」鎸囧畾鐨勬《澶у皬涓哄�硅薄闀垮害锛屽�硅�ラ〉鍐呭瓨杩涜�屽垝鍒嗭紝骞朵娇姣忎釜瀵硅薄鐨勫紑濮�4瀛楄妭璁剧疆

    // 鎴愭寚鍚戜笅涓�瀵硅薄鐨勬寚閽堛��

160                 for (i=PAGE_SIZE/bdir->size; i > 1; i--) {

161                         *((char **) cp) = cp + bdir->size;

162                         cp += bdir->size;

163                 }

    // 鏈�鍚庝竴涓�瀵硅薄寮�濮嬪�勭殑鎸囬拡璁剧疆涓�0(NULL)銆�

    // 鐒跺悗璁╄�ユ《鎻忚堪绗︾殑涓嬩竴鎻忚堪绗︽寚閽堝瓧娈垫寚鍚戝�瑰簲妗剁洰褰曢」鎸囬��chain鎵�鎸囩殑鎻忚堪绗︼紝鑰屾《鐩�褰曠��

    // chain鎸囧悜璇ユ《鎻忚堪绗︼紝涔熷嵆灏嗚�ユ弿杩扮�︽彃鍏ュ埌鎻忚堪绗﹂摼閾惧ご澶勩��

164                 *((char **) cp) = 0;

165                 bdesc->next = bdir->chain; /* OK, link it in! */   /* OK锛屽皢鍏堕摼鍏ワ紒*/

166                 bdir->chain = bdesc;

167         }

    // 杩斿洖鎸囬拡鍗崇瓑浜庤�ユ弿杩扮�﹀�瑰簲椤甸潰鐨勫綋鍓嶇┖闂叉寚閽堛�傜劧鍚庤皟鏁磋�ョ┖闂茬┖闂存寚閽堟寚鍚戜笅涓�涓�绌洪棽瀵硅薄锛�

    // 骞朵娇鎻忚堪绗︿腑瀵瑰簲椤甸潰涓�瀵硅薄寮曠敤璁℃暟澧�1銆�

168         retval = (void *) bdesc->freeptr;

169         bdesc->freeptr = *((void **) retval);

170         bdesc->refcnt++;

    // 鏈�鍚庡紑鏀句腑鏂�锛屽苟杩斿洖鎸囧悜绌洪棽鍐呭瓨瀵硅薄鐨勬寚閽堛��

171         sti();  /* OK, we're safe again */   /* OK锛岀幇鍦ㄦ垜浠�鍙堝畨鍏ㄤ��*/

172         return(retval);

173 }

174

175 /*

176  * Here is the free routine.  If you know the size of the object that you

177  * are freeing, then free_s() will use that information to speed up the

178  * search for the bucket descriptor.

179  *

180  * We will #define a macro so that "free(x)" is becomes "free_s(x, 0)"

181  */

    /*

     * 涓嬮潰鏄�閲婃斁瀛愮▼搴忋�傚�傛灉浣犵煡閬撻噴鏀惧�硅薄鐨勫ぇ灏忥紝鍒�free_s()灏嗕娇鐢ㄨ�ヤ俊鎭�鍔犻��

     * 鎼滃�诲�瑰簲妗舵弿杩扮�︾殑閫熷害銆�

     *

     * 鎴戜滑灏嗗畾涔変竴涓�瀹忥紝浣垮��"free(x)"鎴愪负"free_s(x, 0)"銆�

     */

    //// 閲婃斁瀛樺偍妗跺�硅薄銆�

    // 鍙傛暟锛�obj - 瀵瑰簲瀵硅薄鎸囬拡锛�size - 澶у皬銆�

182 void free_s(void *obj, int size)

183 {

184         void            *page;

185         struct _bucket_dir      *bdir;

186         struct bucket_desc      *bdesc, *prev;

187

188         /* Calculate what page this object lives in */

            /* 璁＄畻璇ュ�硅薄鎵�鍦ㄧ殑椤甸潰 */

189         page = (void *)  ((unsigned long) obj & 0xfffff000);

190         /* Now search the buckets looking for that page */

            /* 鐜板湪鎼滅储瀛樺偍妗剁洰褰曢」鎵�閾炬帴鐨勬《鎻忚堪绗︼紝瀵绘壘璇ラ〉闈� */

    //

191         for (bdir = bucket_dir; bdir->size; bdir++) {

192                 prev = 0;

193                 /* If size is zero then this conditional is always false */

                    /* 濡傛灉鍙傛暟size鏄�0锛屽垯涓嬮潰鏉′欢鑲�瀹氭��false */

194                 if (bdir->size < size)

195                         continue;

    // 鎼滅储瀵瑰簲鐩�褰曢」涓�閾炬帴鐨勬墍鏈夋弿杩扮�︼紝鏌ユ壘瀵瑰簲椤甸潃�傚�傛灉鏌愭弿杩扮�﹂〉闈㈡寚閽堢瓑浜�page鍒欒〃绀烘壘鍒�

    // 浜嗙浉搴旂殑鎻忚堪绗︼紝璺宠浆鍒�found銆傚�傛灉鎻忚堪绗︿笉鍚�鏈夊�瑰��page锛屽垯璁╂弿杩扮�︽寚閽�prev鎸囧悜璇ユ弿杩扮�︺��

196                 for (bdesc = bdir->chain; bdesc; bdesc = bdesc->next) {

197                         if (bdesc->page == page)

198                                 goto found;

199                         prev = bdesc;

200                 }

201         }

    // 鑻ユ悳绱�浜嗗�瑰簲鐩�褰曢」鐨勬墍鏈夋弿杩扮�﹂兘娌℃湁鎵惧埌鎸囧畾鐨勯〉闈�锛屽垯鏄剧ず鍑洪敊淇℃伅锛屾�绘満銆�

202         panic("Bad address passed to kernel free_s()");

203 found:

    // 鎵惧埌瀵瑰簲鐨勬《鎻忚堪绗﹀悗锛岄�栧厛鍏充腑鏂�銆傜劧鍚庡皢璇ュ�硅薄鍐呭瓨鍧楅摼鍏ョ┖闂插潡瀵硅薄閾捐〃涓�锛屽苟浣胯�ユ弿杩扮��

    // 鐨勫�硅薄寮曠敤璁℃暟鍑�1銆�

204         cli(); /* To avoid race conditions */   /* 涓轰簡閬垮厤绔炰簤鏉′欢 */

205         *((void **)obj) = bdesc->freeptr;

206         bdesc->freeptr = obj;

207         bdesc->refcnt--;

    // 濡傛灉寮曠敤璁℃暟宸茬瓑浜�0锛屽垯鎴戜滑灏卞彲浠ラ噴鏀惧�瑰簲鐨勫唴瀛橀〉闈㈠拰璇ユ《鎻忚堪绗︺��

208         if (bdesc->refcnt == 0) {

209                 /*

210                  * We need to make sure that prev is still accurate.  It

211                  * may not be, if someone rudely interrupted us....

212                  */

                    /*

                     * 鎴戜滑闇�瑕佺‘淇�prev浠嶇劧鏄�姝ｇ‘鐨勶紝鑻ユ煇绋嬪簭绮楅瞾鍦颁腑鏂�浜嗘垜浠�

                     * 灏辨湁鍙�鑳戒笉鏄�浜嗐��

                     */

    // 濡傛灉prev宸茬粡涓嶆槸鎼滅储鍒扮殑鎻忚堪绗︾殑鍓嶄竴涓�鎻忚堪绗︼紝鍒欓噸鏂版悳绱㈠綋鍓嶆弿杩扮�︾殑鍓嶄竴涓�鎻忚堪绗︺��

213                 if ((prev && (prev->next != bdesc)) ||

214                     (!prev && (bdir->chain != bdesc)))

215                         for (prev = bdir->chain; prev; prev = prev->next)

216                                 if (prev->next == bdesc)

217                                         break;

    // 濡傛灉鎵惧埌璇ュ墠涓�涓�鎻忚堪绗︼紝鍒欎粠鎻忚堪绗﹂摼涓�鍒犻櫎褰撳墠鎻忚堪绗︺��

218                 if (prev)

219                         prev->next = bdesc->next;

    // 濡傛灉prev==NULL锛屽垯璇存槑褰撳墠涓�涓�鎻忚堪绗︽槸璇ョ洰褰曢」棣栦釜鎻忚堪绗︼紝涔熷嵆鐩�褰曢」涓�chain搴旇�ョ洿鎺�

    // 鎸囧悜褰撳墠鎻忚堪绗�bdesc锛屽惁鍒欒〃绀洪摼琛ㄦ湁闂�棰橈紝鍒欐樉绀哄嚭閿欎俊鎭�锛屾�绘満銆傚洜姝わ紝涓轰簡灏嗗綋鍓嶆弿杩扮��

    // 浠庨摼琛ㄤ腑鍒犻櫎锛屽簲璇ヨ��chain鎸囧悜涓嬩竴涓�鎻忚堪绗︺��

220                 else {

221                         if (bdir->chain != bdesc)

222                                 panic("malloc bucket chains corrupted");

223                         bdir->chain = bdesc->next;

224                 }

    // 閲婃斁褰撳墠鎻忚堪绗︽墍鎿嶄綔鐨勫唴瀛橀〉闈�锛屽苟灏嗚�ユ弿杩扮�︽彃鍏ョ┖闂叉弿杩扮�﹂摼琛ㄥ紑濮嬪�勩��

225                 free_page((unsigned long) bdesc->page);

226                 bdesc->next = free_bucket_desc;

227                 free_bucket_desc = bdesc;

228         }

    // 寮�涓�鏂�锛岃繑鍥炪��

229         sti();

230         return;

231 }

232

233