projects/linux·blob v2.6.32-rc1 · refs

327 lines · 9.2 KiB

1/*
2 * Flexible array managed in PAGE_SIZE parts
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
18 * Copyright IBM Corporation, 2009
19 *
20 * Author: Dave Hansen <[email protected]>
21 */
22
23#include <linux/flex_array.h>
24#include <linux/slab.h>
25#include <linux/stddef.h>
26
27struct flex_array_part {
28 char elements[FLEX_ARRAY_PART_SIZE];
29};
30
31/*
32 * If a user requests an allocation which is small
33 * enough, we may simply use the space in the
34 * flex_array->parts[] array to store the user
35 * data.
36 */
37static inline int elements_fit_in_base(struct flex_array *fa)
38{
39 int data_size = fa->element_size * fa->total_nr_elements;
40 if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
41 return 1;
42 return 0;
43}
44
45/**
46 * flex_array_alloc - allocate a new flexible array
47 * @element_size: the size of individual elements in the array
48 * @total: total number of elements that this should hold
49 * @flags: page allocation flags to use for base array
50 *
51 * Note: all locking must be provided by the caller.
52 *
53 * @total is used to size internal structures. If the user ever
54 * accesses any array indexes >=@total, it will produce errors.
55 *
56 * The maximum number of elements is defined as: the number of
57 * elements that can be stored in a page times the number of
58 * page pointers that we can fit in the base structure or (using
59 * integer math):
60 *
61 * (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
62 *
63 * Here's a table showing example capacities. Note that the maximum
64 * index that the get/put() functions is just nr_objects-1. This
65 * basically means that you get 4MB of storage on 32-bit and 2MB on
66 * 64-bit.
67 *
68 *
69 * Element size | Objects | Objects |
70 * PAGE_SIZE=4k | 32-bit | 64-bit |
71 * ---------------------------------|
72 * 1 bytes | 4186112 | 2093056 |
73 * 2 bytes | 2093056 | 1046528 |
74 * 3 bytes | 1395030 | 697515 |
75 * 4 bytes | 1046528 | 523264 |
76 * 32 bytes | 130816 | 65408 |
77 * 33 bytes | 126728 | 63364 |
78 * 2048 bytes | 2044 | 1022 |
79 * 2049 bytes | 1022 | 511 |
80 * void * | 1046528 | 261632 |
81 *
82 * Since 64-bit pointers are twice the size, we lose half the
83 * capacity in the base structure. Also note that no effort is made
84 * to efficiently pack objects across page boundaries.
85 */
86struct flex_array *flex_array_alloc(int element_size, unsigned int total,
87 gfp_t flags)
88{
89 struct flex_array *ret;
90 int max_size = FLEX_ARRAY_NR_BASE_PTRS *
91 FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
92
93 /* max_size will end up 0 if element_size > PAGE_SIZE */
94 if (total > max_size)
95 return NULL;
96 ret = kzalloc(sizeof(struct flex_array), flags);
97 if (!ret)
98 return NULL;
99 ret->element_size = element_size;
100 ret->total_nr_elements = total;
101 if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
102 memset(ret->parts[0], FLEX_ARRAY_FREE,
103 FLEX_ARRAY_BASE_BYTES_LEFT);
104 return ret;
105}
106
107static int fa_element_to_part_nr(struct flex_array *fa,
108 unsigned int element_nr)
109{
110 return element_nr / FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
111}
112
113/**
114 * flex_array_free_parts - just free the second-level pages
115 * @fa: the flex array from which to free parts
116 *
117 * This is to be used in cases where the base 'struct flex_array'
118 * has been statically allocated and should not be free.
119 */
120void flex_array_free_parts(struct flex_array *fa)
121{
122 int part_nr;
123
124 if (elements_fit_in_base(fa))
125 return;
126 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
127 kfree(fa->parts[part_nr]);
128}
129
130void flex_array_free(struct flex_array *fa)
131{
132 flex_array_free_parts(fa);
133 kfree(fa);
134}
135
136static unsigned int index_inside_part(struct flex_array *fa,
137 unsigned int element_nr)
138{
139 unsigned int part_offset;
140
141 part_offset = element_nr %
142 FLEX_ARRAY_ELEMENTS_PER_PART(fa->element_size);
143 return part_offset * fa->element_size;
144}
145
146static struct flex_array_part *
147__fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
148{
149 struct flex_array_part *part = fa->parts[part_nr];
150 if (!part) {
151 part = kmalloc(sizeof(struct flex_array_part), flags);
152 if (!part)
153 return NULL;
154 if (!(flags & __GFP_ZERO))
155 memset(part, FLEX_ARRAY_FREE,
156 sizeof(struct flex_array_part));
157 fa->parts[part_nr] = part;
158 }
159 return part;
160}
161
162/**
163 * flex_array_put - copy data into the array at @element_nr
164 * @fa: the flex array to copy data into
165 * @element_nr: index of the position in which to insert
166 * the new element.
167 * @src: address of data to copy into the array
168 * @flags: page allocation flags to use for array expansion
169 *
170 *
171 * Note that this *copies* the contents of @src into
172 * the array. If you are trying to store an array of
173 * pointers, make sure to pass in &ptr instead of ptr.
174 *
175 * Locking must be provided by the caller.
176 */
177int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
178 gfp_t flags)
179{
180 int part_nr = fa_element_to_part_nr(fa, element_nr);
181 struct flex_array_part *part;
182 void *dst;
183
184 if (element_nr >= fa->total_nr_elements)
185 return -ENOSPC;
186 if (elements_fit_in_base(fa))
187 part = (struct flex_array_part *)&fa->parts[0];
188 else {
189 part = __fa_get_part(fa, part_nr, flags);
190 if (!part)
191 return -ENOMEM;
192 }
193 dst = &part->elements[index_inside_part(fa, element_nr)];
194 memcpy(dst, src, fa->element_size);
195 return 0;
196}
197
198/**
199 * flex_array_clear - clear element in array at @element_nr
200 * @fa: the flex array of the element.
201 * @element_nr: index of the position to clear.
202 *
203 * Locking must be provided by the caller.
204 */
205int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
206{
207 int part_nr = fa_element_to_part_nr(fa, element_nr);
208 struct flex_array_part *part;
209 void *dst;
210
211 if (element_nr >= fa->total_nr_elements)
212 return -ENOSPC;
213 if (elements_fit_in_base(fa))
214 part = (struct flex_array_part *)&fa->parts[0];
215 else {
216 part = fa->parts[part_nr];
217 if (!part)
218 return -EINVAL;
219 }
220 dst = &part->elements[index_inside_part(fa, element_nr)];
221 memset(dst, FLEX_ARRAY_FREE, fa->element_size);
222 return 0;
223}
224
225/**
226 * flex_array_prealloc - guarantee that array space exists
227 * @fa: the flex array for which to preallocate parts
228 * @start: index of first array element for which space is allocated
229 * @end: index of last (inclusive) element for which space is allocated
230 * @flags: page allocation flags
231 *
232 * This will guarantee that no future calls to flex_array_put()
233 * will allocate memory. It can be used if you are expecting to
234 * be holding a lock or in some atomic context while writing
235 * data into the array.
236 *
237 * Locking must be provided by the caller.
238 */
239int flex_array_prealloc(struct flex_array *fa, unsigned int start,
240 unsigned int end, gfp_t flags)
241{
242 int start_part;
243 int end_part;
244 int part_nr;
245 struct flex_array_part *part;
246
247 if (start >= fa->total_nr_elements || end >= fa->total_nr_elements)
248 return -ENOSPC;
249 if (elements_fit_in_base(fa))
250 return 0;
251 start_part = fa_element_to_part_nr(fa, start);
252 end_part = fa_element_to_part_nr(fa, end);
253 for (part_nr = start_part; part_nr <= end_part; part_nr++) {
254 part = __fa_get_part(fa, part_nr, flags);
255 if (!part)
256 return -ENOMEM;
257 }
258 return 0;
259}
260
261/**
262 * flex_array_get - pull data back out of the array
263 * @fa: the flex array from which to extract data
264 * @element_nr: index of the element to fetch from the array
265 *
266 * Returns a pointer to the data at index @element_nr. Note
267 * that this is a copy of the data that was passed in. If you
268 * are using this to store pointers, you'll get back &ptr.
269 *
270 * Locking must be provided by the caller.
271 */
272void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
273{
274 int part_nr = fa_element_to_part_nr(fa, element_nr);
275 struct flex_array_part *part;
276
277 if (element_nr >= fa->total_nr_elements)
278 return NULL;
279 if (elements_fit_in_base(fa))
280 part = (struct flex_array_part *)&fa->parts[0];
281 else {
282 part = fa->parts[part_nr];
283 if (!part)
284 return NULL;
285 }
286 return &part->elements[index_inside_part(fa, element_nr)];
287}
288
289static int part_is_free(struct flex_array_part *part)
290{
291 int i;
292
293 for (i = 0; i < sizeof(struct flex_array_part); i++)
294 if (part->elements[i] != FLEX_ARRAY_FREE)
295 return 0;
296 return 1;
297}
298
299/**
300 * flex_array_shrink - free unused second-level pages
301 * @fa: the flex array to shrink
302 *
303 * Frees all second-level pages that consist solely of unused
304 * elements. Returns the number of pages freed.
305 *
306 * Locking must be provided by the caller.
307 */
308int flex_array_shrink(struct flex_array *fa)
309{
310 struct flex_array_part *part;
311 int part_nr;
312 int ret = 0;
313
314 if (elements_fit_in_base(fa))
315 return ret;
316 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
317 part = fa->parts[part_nr];
318 if (!part)
319 continue;
320 if (part_is_free(part)) {
321 fa->parts[part_nr] = NULL;
322 kfree(part);
323 ret++;
324 }
325 }
326 return ret;
327}