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
|
#include <slab_alloc.h>
typedef struct object {
struct object *next;
} object_t;
typedef struct cache {
struct { // pack this so that it takes less space...
uint32_t is_a_cache : 1; // if not, this is a region allocated alone
uint32_t n_free_objs : 31;
};
union {
struct { // when this is a cache
object_t* first_free_obj;
struct cache *next_cache;
} c;
struct { // when this is a region allocated alone
size_t region_size;
} sr;
};
void* region_addr;
struct cache *next_region;
} cache_t;
typedef struct slab {
cache_t *first_cache; // linked list of caches
} slab_t;
struct mem_allocator {
const slab_type_t *types;
slab_t *slabs;
cache_t *first_free_region_descriptor;
cache_t *all_regions;
page_alloc_fun_t alloc_fun;
page_free_fun_t free_fun;
};
// ============================================== //
// Helper functions for the manipulation of lists //
// ============================================== //
void add_free_region_descriptor(mem_allocator_t *a, cache_t *c) {
c->next_region = a->first_free_region_descriptor;
a->first_free_region_descriptor = c;
}
cache_t *take_region_descriptor(mem_allocator_t *a) {
if (a->first_free_region_descriptor == 0) {
// TODO : allocate more descriptors (not complicated)
return 0;
}
cache_t *x = a->first_free_region_descriptor;
a->first_free_region_descriptor = x->next_region;
return x;
}
// ============================== //
// The actual allocator functions //
// ============================== //
mem_allocator_t* create_slab_allocator(const slab_type_t *types, page_alloc_fun_t af, page_free_fun_t ff) {
union {
void* addr;
mem_allocator_t *a;
slab_t *s;
cache_t *c;
} ptr;
ptr.addr = af(PAGE_SIZE);
if (ptr.addr == 0) return 0; // could not allocate
void* end_addr = ptr.addr + PAGE_SIZE;
mem_allocator_t *a = ptr.a;
ptr.a++;
a->all_regions = 0;
a->alloc_fun = af;
a->free_fun = ff;
a->types = types;
a->slabs = ptr.s;
for (const slab_type_t *t = types; t->obj_size != 0; t++) {
ptr.s->first_cache = 0;
ptr.s++;
}
a->first_free_region_descriptor = 0;
while ((void*)(ptr.c + 1) <= end_addr) {
add_free_region_descriptor(a, ptr.c);
ptr.c++;
}
return a;
}
static void stack_and_destroy_regions(page_free_fun_t ff, cache_t *r) {
if (r == 0) return;
void* addr = r->region_addr;
stack_and_destroy_regions(ff, r->next_region);
ff(addr);
}
void destroy_slab_allocator(mem_allocator_t *a) {
stack_and_destroy_regions(a->free_fun, a->all_regions);
a->free_fun(a);
}
void* slab_alloc(mem_allocator_t* a, size_t sz) {
for (int i = 0; a->types[i].obj_size != 0; i++) {
const size_t obj_size = a->types[i].obj_size;
if (sz <= obj_size) {
// find a cache with free space
cache_t *fc = a->slabs[i].first_cache;
while (fc != 0 && fc->n_free_objs == 0) {
ASSERT(fc->c.first_free_obj == 0); // make sure n_free == 0 iff no object in the free stack
fc = fc->c.next_cache;
}
// if none found, try to allocate a new one
if (fc == 0) {
fc = take_region_descriptor(a);
if (fc == 0) return 0;
const size_t cache_size = a->types[i].pages_per_cache * PAGE_SIZE;
fc->region_addr = a->alloc_fun(cache_size);
if (fc->region_addr == 0) {
add_free_region_descriptor(a, fc);
return 0;
}
fc->is_a_cache = 1;
fc->n_free_objs = 0;
fc->c.first_free_obj = 0;
for (void* i = fc->region_addr; i + obj_size <= fc->region_addr + cache_size; i += obj_size) {
object_t *x = (object_t*)i;
x->next = fc->c.first_free_obj;
fc->c.first_free_obj = x;
fc->n_free_objs++;
}
ASSERT(fc->n_free_objs == cache_size / obj_size);
fc->next_region = a->all_regions;
a->all_regions = fc;
fc->c.next_cache = a->slabs[i].first_cache;
a->slabs[i].first_cache = fc;
}
// allocate on fc
ASSERT(fc != 0 && fc->n_free_objs > 0);
object_t *x = fc->c.first_free_obj;
fc->c.first_free_obj = x->next;
fc->n_free_objs--;
// TODO : if fc is full, put it at the end
return x;
}
}
// otherwise directly allocate using a->alloc_fun
cache_t *r = take_region_descriptor(a);
if (r == 0) return 0;
r->region_addr = a->alloc_fun(sz);
if (r->region_addr == 0) {
add_free_region_descriptor(a, r);
return 0;
} else {
r->is_a_cache = 0;
r->sr.region_size = sz;
r->next_region = a->all_regions;
a->all_regions = r;
return (void*)r->region_addr;
}
}
void slab_free(mem_allocator_t* a, void* addr) {
for (int i = 0; a->types[i].obj_size != 0; i++) {
size_t region_size = PAGE_SIZE * a->types[i].pages_per_cache;
for (cache_t *r = a->slabs[i].first_cache; r != 0; r = r->c.next_cache) {
if (addr >= r->region_addr && addr < r->region_addr + region_size) {
ASSERT((addr - r->region_addr) % a->types[i].obj_size == 0);
ASSERT(r->is_a_cache);
object_t *o = (object_t*)addr;
o->next = r->c.first_free_obj;
r->c.first_free_obj = o;
r->n_free_objs++;
// TODO : if cache is empty, free it
return;
}
}
}
// otherwise the block was directly allocated : look for it in regions.
a->free_fun(addr);
ASSERT(a->all_regions != 0);
if (a->all_regions->region_addr == addr) {
cache_t *r = a->all_regions;
ASSERT(r->is_a_cache == 0);
a->all_regions = r->next_region;
add_free_region_descriptor(a, r);
} else {
for (cache_t *i = a->all_regions; i->next_region != 0; i = i->next_region) {
if (i->next_region->region_addr == addr) {
cache_t *r = i->next_region;
ASSERT(r->is_a_cache == 0);
i->next_region = r->next_region;
add_free_region_descriptor(a, r);
return;
}
}
ASSERT(false);
}
}
|
