about summary refs log tree commit diff
path: root/src/malloc/mallocng/malloc.c
blob: d695ab8ec98216d3420e41b820f951c9474adca4 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
#include <stdlib.h>
#include <stdint.h>
#include <limits.h>
#include <string.h>
#include <sys/mman.h>
#include <errno.h>

#include "meta.h"

LOCK_OBJ_DEF;

const uint16_t size_classes[] = {
	1, 2, 3, 4, 5, 6, 7, 8,
	9, 10, 12, 15,
	18, 20, 25, 31,
	36, 42, 50, 63,
	72, 84, 102, 127,
	146, 170, 204, 255,
	292, 340, 409, 511,
	584, 682, 818, 1023,
	1169, 1364, 1637, 2047,
	2340, 2730, 3276, 4095,
	4680, 5460, 6552, 8191,
};

static const uint8_t small_cnt_tab[][3] = {
	{ 30, 30, 30 },
	{ 31, 15, 15 },
	{ 20, 10, 10 },
	{ 31, 15, 7 },
	{ 25, 12, 6 },
	{ 21, 10, 5 },
	{ 18, 8, 4 },
	{ 31, 15, 7 },
	{ 28, 14, 6 },
};

static const uint8_t med_cnt_tab[4] = { 28, 24, 20, 32 };

struct malloc_context ctx = { 0 };

struct meta *alloc_meta(void)
{
	struct meta *m;
	unsigned char *p;
	if (!ctx.init_done) {
#ifndef PAGESIZE
		ctx.pagesize = get_page_size();
#endif
		ctx.secret = get_random_secret();
		ctx.init_done = 1;
	}
	size_t pagesize = PGSZ;
	if (pagesize < 4096) pagesize = 4096;
	if ((m = dequeue_head(&ctx.free_meta_head))) return m;
	if (!ctx.avail_meta_count) {
		int need_unprotect = 1;
		if (!ctx.avail_meta_area_count && ctx.brk!=-1) {
			uintptr_t new = ctx.brk + pagesize;
			int need_guard = 0;
			if (!ctx.brk) {
				need_guard = 1;
				ctx.brk = brk(0);
				// some ancient kernels returned _ebss
				// instead of next page as initial brk.
				ctx.brk += -ctx.brk & (pagesize-1);
				new = ctx.brk + 2*pagesize;
			}
			if (brk(new) != new) {
				ctx.brk = -1;
			} else {
				if (need_guard) mmap((void *)ctx.brk, pagesize,
					PROT_NONE, MAP_ANON|MAP_PRIVATE|MAP_FIXED, -1, 0);
				ctx.brk = new;
				ctx.avail_meta_areas = (void *)(new - pagesize);
				ctx.avail_meta_area_count = pagesize>>12;
				need_unprotect = 0;
			}
		}
		if (!ctx.avail_meta_area_count) {
			size_t n = 2UL << ctx.meta_alloc_shift;
			p = mmap(0, n*pagesize, PROT_NONE,
				MAP_PRIVATE|MAP_ANON, -1, 0);
			if (p==MAP_FAILED) return 0;
			ctx.avail_meta_areas = p + pagesize;
			ctx.avail_meta_area_count = (n-1)*(pagesize>>12);
			ctx.meta_alloc_shift++;
		}
		p = ctx.avail_meta_areas;
		if ((uintptr_t)p & (pagesize-1)) need_unprotect = 0;
		if (need_unprotect)
			if (mprotect(p, pagesize, PROT_READ|PROT_WRITE)
			    && errno != ENOSYS)
				return 0;
		ctx.avail_meta_area_count--;
		ctx.avail_meta_areas = p + 4096;
		if (ctx.meta_area_tail) {
			ctx.meta_area_tail->next = (void *)p;
		} else {
			ctx.meta_area_head = (void *)p;
		}
		ctx.meta_area_tail = (void *)p;
		ctx.meta_area_tail->check = ctx.secret;
		ctx.avail_meta_count = ctx.meta_area_tail->nslots
			= (4096-sizeof(struct meta_area))/sizeof *m;
		ctx.avail_meta = ctx.meta_area_tail->slots;
	}
	ctx.avail_meta_count--;
	m = ctx.avail_meta++;
	m->prev = m->next = 0;
	return m;
}

static uint32_t try_avail(struct meta **pm)
{
	struct meta *m = *pm;
	uint32_t first;
	if (!m) return 0;
	uint32_t mask = m->avail_mask;
	if (!mask) {
		if (!m) return 0;
		if (!m->freed_mask) {
			dequeue(pm, m);
			m = *pm;
			if (!m) return 0;
		} else {
			m = m->next;
			*pm = m;
		}

		mask = m->freed_mask;

		// skip fully-free group unless it's the only one
		// or it's a permanently non-freeable group
		if (mask == (2u<<m->last_idx)-1 && m->freeable) {
			m = m->next;
			*pm = m;
			mask = m->freed_mask;
		}

		// activate more slots in a not-fully-active group
		// if needed, but only as a last resort. prefer using
		// any other group with free slots. this avoids
		// touching & dirtying as-yet-unused pages.
		if (!(mask & ((2u<<m->mem->active_idx)-1))) {
			if (m->next != m) {
				m = m->next;
				*pm = m;
			} else {
				int cnt = m->mem->active_idx + 2;
				int size = size_classes[m->sizeclass]*UNIT;
				int span = UNIT + size*cnt;
				// activate up to next 4k boundary
				while ((span^(span+size-1)) < 4096) {
					cnt++;
					span += size;
				}
				if (cnt > m->last_idx+1)
					cnt = m->last_idx+1;
				m->mem->active_idx = cnt-1;
			}
		}
		mask = activate_group(m);
		assert(mask);
		decay_bounces(m->sizeclass);
	}
	first = mask&-mask;
	m->avail_mask = mask-first;
	return first;
}

static int alloc_slot(int, size_t);

static struct meta *alloc_group(int sc, size_t req)
{
	size_t size = UNIT*size_classes[sc];
	int i = 0, cnt;
	unsigned char *p;
	struct meta *m = alloc_meta();
	if (!m) return 0;
	size_t usage = ctx.usage_by_class[sc];
	size_t pagesize = PGSZ;
	int active_idx;
	if (sc < 9) {
		while (i<2 && 4*small_cnt_tab[sc][i] > usage)
			i++;
		cnt = small_cnt_tab[sc][i];
	} else {
		// lookup max number of slots fitting in power-of-two size
		// from a table, along with number of factors of two we
		// can divide out without a remainder or reaching 1.
		cnt = med_cnt_tab[sc&3];

		// reduce cnt to avoid excessive eagar allocation.
		while (!(cnt&1) && 4*cnt > usage)
			cnt >>= 1;

		// data structures don't support groups whose slot offsets
		// in units don't fit in 16 bits.
		while (size*cnt >= 65536*UNIT)
			cnt >>= 1;
	}

	// If we selected a count of 1 above but it's not sufficient to use
	// mmap, increase to 2. Then it might be; if not it will nest.
	if (cnt==1 && size*cnt+UNIT <= pagesize/2) cnt = 2;

	// All choices of size*cnt are "just below" a power of two, so anything
	// larger than half the page size should be allocated as whole pages.
	if (size*cnt+UNIT > pagesize/2) {
		// check/update bounce counter to start/increase retention
		// of freed maps, and inhibit use of low-count, odd-size
		// small mappings and single-slot groups if activated.
		int nosmall = is_bouncing(sc);
		account_bounce(sc);
		step_seq();

		// since the following count reduction opportunities have
		// an absolute memory usage cost, don't overdo them. count
		// coarse usage as part of usage.
		if (!(sc&1) && sc<32) usage += ctx.usage_by_class[sc+1];

		// try to drop to a lower count if the one found above
		// increases usage by more than 25%. these reduced counts
		// roughly fill an integral number of pages, just not a
		// power of two, limiting amount of unusable space.
		if (4*cnt > usage && !nosmall) {
			if (0);
			else if ((sc&3)==1 && size*cnt>8*pagesize) cnt = 2;
			else if ((sc&3)==2 && size*cnt>4*pagesize) cnt = 3;
			else if ((sc&3)==0 && size*cnt>8*pagesize) cnt = 3;
			else if ((sc&3)==0 && size*cnt>2*pagesize) cnt = 5;
		}
		size_t needed = size*cnt + UNIT;
		needed += -needed & (pagesize-1);

		// produce an individually-mmapped allocation if usage is low,
		// bounce counter hasn't triggered, and either it saves memory
		// or it avoids eagar slot allocation without wasting too much.
		if (!nosmall && cnt<=7) {
			req += IB + UNIT;
			req += -req & (pagesize-1);
			if (req<size+UNIT || (req>=4*pagesize && 2*cnt>usage)) {
				cnt = 1;
				needed = req;
			}
		}

		p = mmap(0, needed, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
		if (p==MAP_FAILED) {
			free_meta(m);
			return 0;
		}
		m->maplen = needed>>12;
		ctx.mmap_counter++;
		active_idx = (4096-UNIT)/size-1;
		if (active_idx > cnt-1) active_idx = cnt-1;
		if (active_idx < 0) active_idx = 0;
	} else {
		int j = size_to_class(UNIT+cnt*size-IB);
		int idx = alloc_slot(j, UNIT+cnt*size-IB);
		if (idx < 0) {
			free_meta(m);
			return 0;
		}
		struct meta *g = ctx.active[j];
		p = enframe(g, idx, UNIT*size_classes[j]-IB, ctx.mmap_counter);
		m->maplen = 0;
		p[-3] = (p[-3]&31) | (6<<5);
		for (int i=0; i<=cnt; i++)
			p[UNIT+i*size-4] = 0;
		active_idx = cnt-1;
	}
	ctx.usage_by_class[sc] += cnt;
	m->avail_mask = (2u<<active_idx)-1;
	m->freed_mask = (2u<<(cnt-1))-1 - m->avail_mask;
	m->mem = (void *)p;
	m->mem->meta = m;
	m->mem->active_idx = active_idx;
	m->last_idx = cnt-1;
	m->freeable = 1;
	m->sizeclass = sc;
	return m;
}

static int alloc_slot(int sc, size_t req)
{
	uint32_t first = try_avail(&ctx.active[sc]);
	if (first) return a_ctz_32(first);

	struct meta *g = alloc_group(sc, req);
	if (!g) return -1;

	g->avail_mask--;
	queue(&ctx.active[sc], g);
	return 0;
}

void *malloc(size_t n)
{
	if (size_overflows(n)) return 0;
	struct meta *g;
	uint32_t mask, first;
	int sc;
	int idx;
	int ctr;

	if (n >= MMAP_THRESHOLD) {
		size_t needed = n + IB + UNIT;
		void *p = mmap(0, needed, PROT_READ|PROT_WRITE,
			MAP_PRIVATE|MAP_ANON, -1, 0);
		if (p==MAP_FAILED) return 0;
		wrlock();
		step_seq();
		g = alloc_meta();
		if (!g) {
			unlock();
			munmap(p, needed);
			return 0;
		}
		g->mem = p;
		g->mem->meta = g;
		g->last_idx = 0;
		g->freeable = 1;
		g->sizeclass = 63;
		g->maplen = (needed+4095)/4096;
		g->avail_mask = g->freed_mask = 0;
		// use a global counter to cycle offset in
		// individually-mmapped allocations.
		ctx.mmap_counter++;
		idx = 0;
		goto success;
	}

	sc = size_to_class(n);

	rdlock();
	g = ctx.active[sc];

	// use coarse size classes initially when there are not yet
	// any groups of desired size. this allows counts of 2 or 3
	// to be allocated at first rather than having to start with
	// 7 or 5, the min counts for even size classes.
	if (!g && sc>=4 && sc<32 && sc!=6 && !(sc&1) && !ctx.usage_by_class[sc]) {
		size_t usage = ctx.usage_by_class[sc|1];
		// if a new group may be allocated, count it toward
		// usage in deciding if we can use coarse class.
		if (!ctx.active[sc|1] || (!ctx.active[sc|1]->avail_mask
		    && !ctx.active[sc|1]->freed_mask))
			usage += 3;
		if (usage <= 12)
			sc |= 1;
		g = ctx.active[sc];
	}

	for (;;) {
		mask = g ? g->avail_mask : 0;
		first = mask&-mask;
		if (!first) break;
		if (RDLOCK_IS_EXCLUSIVE || !MT)
			g->avail_mask = mask-first;
		else if (a_cas(&g->avail_mask, mask, mask-first)!=mask)
			continue;
		idx = a_ctz_32(first);
		goto success;
	}
	upgradelock();

	idx = alloc_slot(sc, n);
	if (idx < 0) {
		unlock();
		return 0;
	}
	g = ctx.active[sc];

success:
	ctr = ctx.mmap_counter;
	unlock();
	return enframe(g, idx, n, ctr);
}

int is_allzero(void *p)
{
	struct meta *g = get_meta(p);
	return g->sizeclass >= 48 ||
		get_stride(g) < UNIT*size_classes[g->sizeclass];
}