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8d063cd8 LW |
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 |