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1 | /* $Header: malloc.c,v 1.0 87/12/18 13:05:35 root Exp $ |
2 | * |
3 | * $Log: malloc.c,v $ |
4 | * Revision 1.0 87/12/18 13:05:35 root |
5 | * Initial revision |
6 | * |
7 | */ |
8 | |
9 | #ifndef lint |
10 | static char sccsid[] = "@(#)malloc.c 4.3 (Berkeley) 9/16/83"; |
11 | #endif |
12 | #include <stdio.h> |
13 | |
14 | #define RCHECK |
15 | /* |
16 | * malloc.c (Caltech) 2/21/82 |
17 | * Chris Kingsley, kingsley@cit-20. |
18 | * |
19 | * This is a very fast storage allocator. It allocates blocks of a small |
20 | * number of different sizes, and keeps free lists of each size. Blocks that |
21 | * don't exactly fit are passed up to the next larger size. In this |
22 | * implementation, the available sizes are 2^n-4 (or 2^n-12) bytes long. |
23 | * This is designed for use in a program that uses vast quantities of memory, |
24 | * but bombs when it runs out. |
25 | */ |
26 | |
27 | #include <sys/types.h> |
28 | |
29 | #define NULL 0 |
30 | |
31 | /* |
32 | * The overhead on a block is at least 4 bytes. When free, this space |
33 | * contains a pointer to the next free block, and the bottom two bits must |
34 | * be zero. When in use, the first byte is set to MAGIC, and the second |
35 | * byte is the size index. The remaining bytes are for alignment. |
36 | * If range checking is enabled and the size of the block fits |
37 | * in two bytes, then the top two bytes hold the size of the requested block |
38 | * plus the range checking words, and the header word MINUS ONE. |
39 | */ |
40 | union overhead { |
41 | union overhead *ov_next; /* when free */ |
42 | struct { |
43 | u_char ovu_magic; /* magic number */ |
44 | u_char ovu_index; /* bucket # */ |
45 | #ifdef RCHECK |
46 | u_short ovu_size; /* actual block size */ |
47 | u_int ovu_rmagic; /* range magic number */ |
48 | #endif |
49 | } ovu; |
50 | #define ov_magic ovu.ovu_magic |
51 | #define ov_index ovu.ovu_index |
52 | #define ov_size ovu.ovu_size |
53 | #define ov_rmagic ovu.ovu_rmagic |
54 | }; |
55 | |
56 | #define MAGIC 0xff /* magic # on accounting info */ |
57 | #define RMAGIC 0x55555555 /* magic # on range info */ |
58 | #ifdef RCHECK |
59 | #define RSLOP sizeof (u_int) |
60 | #else |
61 | #define RSLOP 0 |
62 | #endif |
63 | |
64 | /* |
65 | * nextf[i] is the pointer to the next free block of size 2^(i+3). The |
66 | * smallest allocatable block is 8 bytes. The overhead information |
67 | * precedes the data area returned to the user. |
68 | */ |
69 | #define NBUCKETS 30 |
70 | static union overhead *nextf[NBUCKETS]; |
71 | extern char *sbrk(); |
72 | |
73 | #ifdef MSTATS |
74 | /* |
75 | * nmalloc[i] is the difference between the number of mallocs and frees |
76 | * for a given block size. |
77 | */ |
78 | static u_int nmalloc[NBUCKETS]; |
79 | #include <stdio.h> |
80 | #endif |
81 | |
82 | #ifdef debug |
83 | #define ASSERT(p) if (!(p)) botch("p"); else |
84 | static |
85 | botch(s) |
86 | char *s; |
87 | { |
88 | |
89 | printf("assertion botched: %s\n", s); |
90 | abort(); |
91 | } |
92 | #else |
93 | #define ASSERT(p) |
94 | #endif |
95 | |
96 | char * |
97 | malloc(nbytes) |
98 | register unsigned nbytes; |
99 | { |
100 | register union overhead *p; |
101 | register int bucket = 0; |
102 | register unsigned shiftr; |
103 | |
104 | /* |
105 | * Convert amount of memory requested into |
106 | * closest block size stored in hash buckets |
107 | * which satisfies request. Account for |
108 | * space used per block for accounting. |
109 | */ |
110 | nbytes += sizeof (union overhead) + RSLOP; |
111 | nbytes = (nbytes + 3) &~ 3; |
112 | shiftr = (nbytes - 1) >> 2; |
113 | /* apart from this loop, this is O(1) */ |
114 | while (shiftr >>= 1) |
115 | bucket++; |
116 | /* |
117 | * If nothing in hash bucket right now, |
118 | * request more memory from the system. |
119 | */ |
120 | if (nextf[bucket] == NULL) |
121 | morecore(bucket); |
122 | if ((p = (union overhead *)nextf[bucket]) == NULL) |
123 | return (NULL); |
124 | /* remove from linked list */ |
125 | if (*((int*)p) > 0x10000000) |
126 | fprintf(stderr,"Corrupt malloc ptr 0x%x at 0x%x\n",*((int*)p),p); |
127 | nextf[bucket] = nextf[bucket]->ov_next; |
128 | p->ov_magic = MAGIC; |
129 | p->ov_index= bucket; |
130 | #ifdef MSTATS |
131 | nmalloc[bucket]++; |
132 | #endif |
133 | #ifdef RCHECK |
134 | /* |
135 | * Record allocated size of block and |
136 | * bound space with magic numbers. |
137 | */ |
138 | if (nbytes <= 0x10000) |
139 | p->ov_size = nbytes - 1; |
140 | p->ov_rmagic = RMAGIC; |
141 | *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC; |
142 | #endif |
143 | return ((char *)(p + 1)); |
144 | } |
145 | |
146 | /* |
147 | * Allocate more memory to the indicated bucket. |
148 | */ |
149 | static |
150 | morecore(bucket) |
151 | register bucket; |
152 | { |
153 | register union overhead *op; |
154 | register int rnu; /* 2^rnu bytes will be requested */ |
155 | register int nblks; /* become nblks blocks of the desired size */ |
156 | register int siz; |
157 | |
158 | if (nextf[bucket]) |
159 | return; |
160 | /* |
161 | * Insure memory is allocated |
162 | * on a page boundary. Should |
163 | * make getpageize call? |
164 | */ |
165 | op = (union overhead *)sbrk(0); |
166 | if ((int)op & 0x3ff) |
167 | sbrk(1024 - ((int)op & 0x3ff)); |
168 | /* take 2k unless the block is bigger than that */ |
169 | rnu = (bucket <= 8) ? 11 : bucket + 3; |
170 | nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */ |
171 | if (rnu < bucket) |
172 | rnu = bucket; |
173 | op = (union overhead *)sbrk(1 << rnu); |
174 | /* no more room! */ |
175 | if ((int)op == -1) |
176 | return; |
177 | /* |
178 | * Round up to minimum allocation size boundary |
179 | * and deduct from block count to reflect. |
180 | */ |
181 | if ((int)op & 7) { |
182 | op = (union overhead *)(((int)op + 8) &~ 7); |
183 | nblks--; |
184 | } |
185 | /* |
186 | * Add new memory allocated to that on |
187 | * free list for this hash bucket. |
188 | */ |
189 | nextf[bucket] = op; |
190 | siz = 1 << (bucket + 3); |
191 | while (--nblks > 0) { |
192 | op->ov_next = (union overhead *)((caddr_t)op + siz); |
193 | op = (union overhead *)((caddr_t)op + siz); |
194 | } |
195 | } |
196 | |
197 | free(cp) |
198 | char *cp; |
199 | { |
200 | register int size; |
201 | register union overhead *op; |
202 | |
203 | if (cp == NULL) |
204 | return; |
205 | op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); |
206 | #ifdef debug |
207 | ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ |
208 | #else |
209 | if (op->ov_magic != MAGIC) |
210 | return; /* sanity */ |
211 | #endif |
212 | #ifdef RCHECK |
213 | ASSERT(op->ov_rmagic == RMAGIC); |
214 | if (op->ov_index <= 13) |
215 | ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC); |
216 | #endif |
217 | ASSERT(op->ov_index < NBUCKETS); |
218 | size = op->ov_index; |
219 | op->ov_next = nextf[size]; |
220 | nextf[size] = op; |
221 | #ifdef MSTATS |
222 | nmalloc[size]--; |
223 | #endif |
224 | } |
225 | |
226 | /* |
227 | * When a program attempts "storage compaction" as mentioned in the |
228 | * old malloc man page, it realloc's an already freed block. Usually |
229 | * this is the last block it freed; occasionally it might be farther |
230 | * back. We have to search all the free lists for the block in order |
231 | * to determine its bucket: 1st we make one pass thru the lists |
232 | * checking only the first block in each; if that fails we search |
233 | * ``realloc_srchlen'' blocks in each list for a match (the variable |
234 | * is extern so the caller can modify it). If that fails we just copy |
235 | * however many bytes was given to realloc() and hope it's not huge. |
236 | */ |
237 | int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */ |
238 | |
239 | char * |
240 | realloc(cp, nbytes) |
241 | char *cp; |
242 | unsigned nbytes; |
243 | { |
244 | register u_int onb; |
245 | union overhead *op; |
246 | char *res; |
247 | register int i; |
248 | int was_alloced = 0; |
249 | |
250 | if (cp == NULL) |
251 | return (malloc(nbytes)); |
252 | op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); |
253 | if (op->ov_magic == MAGIC) { |
254 | was_alloced++; |
255 | i = op->ov_index; |
256 | } else { |
257 | /* |
258 | * Already free, doing "compaction". |
259 | * |
260 | * Search for the old block of memory on the |
261 | * free list. First, check the most common |
262 | * case (last element free'd), then (this failing) |
263 | * the last ``realloc_srchlen'' items free'd. |
264 | * If all lookups fail, then assume the size of |
265 | * the memory block being realloc'd is the |
266 | * smallest possible. |
267 | */ |
268 | if ((i = findbucket(op, 1)) < 0 && |
269 | (i = findbucket(op, realloc_srchlen)) < 0) |
270 | i = 0; |
271 | } |
272 | onb = (1 << (i + 3)) - sizeof (*op) - RSLOP; |
273 | /* avoid the copy if same size block */ |
274 | if (was_alloced && |
275 | nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP) |
276 | return(cp); |
277 | if ((res = malloc(nbytes)) == NULL) |
278 | return (NULL); |
279 | if (cp != res) /* common optimization */ |
280 | bcopy(cp, res, (nbytes < onb) ? nbytes : onb); |
281 | if (was_alloced) |
282 | free(cp); |
283 | return (res); |
284 | } |
285 | |
286 | /* |
287 | * Search ``srchlen'' elements of each free list for a block whose |
288 | * header starts at ``freep''. If srchlen is -1 search the whole list. |
289 | * Return bucket number, or -1 if not found. |
290 | */ |
291 | static |
292 | findbucket(freep, srchlen) |
293 | union overhead *freep; |
294 | int srchlen; |
295 | { |
296 | register union overhead *p; |
297 | register int i, j; |
298 | |
299 | for (i = 0; i < NBUCKETS; i++) { |
300 | j = 0; |
301 | for (p = nextf[i]; p && j != srchlen; p = p->ov_next) { |
302 | if (p == freep) |
303 | return (i); |
304 | j++; |
305 | } |
306 | } |
307 | return (-1); |
308 | } |
309 | |
310 | #ifdef MSTATS |
311 | /* |
312 | * mstats - print out statistics about malloc |
313 | * |
314 | * Prints two lines of numbers, one showing the length of the free list |
315 | * for each size category, the second showing the number of mallocs - |
316 | * frees for each size category. |
317 | */ |
318 | mstats(s) |
319 | char *s; |
320 | { |
321 | register int i, j; |
322 | register union overhead *p; |
323 | int totfree = 0, |
324 | totused = 0; |
325 | |
326 | fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s); |
327 | for (i = 0; i < NBUCKETS; i++) { |
328 | for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) |
329 | ; |
330 | fprintf(stderr, " %d", j); |
331 | totfree += j * (1 << (i + 3)); |
332 | } |
333 | fprintf(stderr, "\nused:\t"); |
334 | for (i = 0; i < NBUCKETS; i++) { |
335 | fprintf(stderr, " %d", nmalloc[i]); |
336 | totused += nmalloc[i] * (1 << (i + 3)); |
337 | } |
338 | fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n", |
339 | totused, totfree); |
340 | } |
341 | #endif |