2 * Flexible array managed in PAGE_SIZE parts
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.
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.
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.
18 * Copyright IBM Corporation, 2009
20 * Author: Dave Hansen <dave@linux.vnet.ibm.com>
23 #include <linux/flex_array.h>
24 #include <linux/slab.h>
25 #include <linux/stddef.h>
26 #include <linux/export.h>
27 #include <linux/reciprocal_div.h>
29 struct flex_array_part {
30 char elements[FLEX_ARRAY_PART_SIZE];
34 * If a user requests an allocation which is small
35 * enough, we may simply use the space in the
36 * flex_array->parts[] array to store the user
39 static inline int elements_fit_in_base(struct flex_array *fa)
41 int data_size = fa->element_size * fa->total_nr_elements;
42 if (data_size <= FLEX_ARRAY_BASE_BYTES_LEFT)
48 * flex_array_alloc - allocate a new flexible array
49 * @element_size: the size of individual elements in the array
50 * @total: total number of elements that this should hold
51 * @flags: page allocation flags to use for base array
53 * Note: all locking must be provided by the caller.
55 * @total is used to size internal structures. If the user ever
56 * accesses any array indexes >=@total, it will produce errors.
58 * The maximum number of elements is defined as: the number of
59 * elements that can be stored in a page times the number of
60 * page pointers that we can fit in the base structure or (using
63 * (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
65 * Here's a table showing example capacities. Note that the maximum
66 * index that the get/put() functions is just nr_objects-1. This
67 * basically means that you get 4MB of storage on 32-bit and 2MB on
71 * Element size | Objects | Objects |
72 * PAGE_SIZE=4k | 32-bit | 64-bit |
73 * ---------------------------------|
74 * 1 bytes | 4177920 | 2088960 |
75 * 2 bytes | 2088960 | 1044480 |
76 * 3 bytes | 1392300 | 696150 |
77 * 4 bytes | 1044480 | 522240 |
78 * 32 bytes | 130560 | 65408 |
79 * 33 bytes | 126480 | 63240 |
80 * 2048 bytes | 2040 | 1020 |
81 * 2049 bytes | 1020 | 510 |
82 * void * | 1044480 | 261120 |
84 * Since 64-bit pointers are twice the size, we lose half the
85 * capacity in the base structure. Also note that no effort is made
86 * to efficiently pack objects across page boundaries.
88 struct flex_array *flex_array_alloc(int element_size, unsigned int total,
91 struct flex_array *ret;
92 int elems_per_part = 0;
94 struct reciprocal_value reciprocal_elems = { 0 };
97 elems_per_part = FLEX_ARRAY_ELEMENTS_PER_PART(element_size);
98 reciprocal_elems = reciprocal_value(elems_per_part);
99 max_size = FLEX_ARRAY_NR_BASE_PTRS * elems_per_part;
102 /* max_size will end up 0 if element_size > PAGE_SIZE */
103 if (total > max_size)
105 ret = kzalloc(sizeof(struct flex_array), flags);
108 ret->element_size = element_size;
109 ret->total_nr_elements = total;
110 ret->elems_per_part = elems_per_part;
111 ret->reciprocal_elems = reciprocal_elems;
112 if (elements_fit_in_base(ret) && !(flags & __GFP_ZERO))
113 memset(&ret->parts[0], FLEX_ARRAY_FREE,
114 FLEX_ARRAY_BASE_BYTES_LEFT);
117 EXPORT_SYMBOL(flex_array_alloc);
119 static int fa_element_to_part_nr(struct flex_array *fa,
120 unsigned int element_nr)
123 * if element_size == 0 we don't get here, so we never touch
124 * the zeroed fa->reciprocal_elems, which would yield invalid
127 return reciprocal_divide(element_nr, fa->reciprocal_elems);
131 * flex_array_free_parts - just free the second-level pages
132 * @fa: the flex array from which to free parts
134 * This is to be used in cases where the base 'struct flex_array'
135 * has been statically allocated and should not be free.
137 void flex_array_free_parts(struct flex_array *fa)
141 if (elements_fit_in_base(fa))
143 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++)
144 kfree(fa->parts[part_nr]);
146 EXPORT_SYMBOL(flex_array_free_parts);
148 void flex_array_free(struct flex_array *fa)
150 flex_array_free_parts(fa);
153 EXPORT_SYMBOL(flex_array_free);
155 static unsigned int index_inside_part(struct flex_array *fa,
156 unsigned int element_nr,
157 unsigned int part_nr)
159 unsigned int part_offset;
161 part_offset = element_nr - part_nr * fa->elems_per_part;
162 return part_offset * fa->element_size;
165 static struct flex_array_part *
166 __fa_get_part(struct flex_array *fa, int part_nr, gfp_t flags)
168 struct flex_array_part *part = fa->parts[part_nr];
170 part = kmalloc(sizeof(struct flex_array_part), flags);
173 if (!(flags & __GFP_ZERO))
174 memset(part, FLEX_ARRAY_FREE,
175 sizeof(struct flex_array_part));
176 fa->parts[part_nr] = part;
182 * flex_array_put - copy data into the array at @element_nr
183 * @fa: the flex array to copy data into
184 * @element_nr: index of the position in which to insert
186 * @src: address of data to copy into the array
187 * @flags: page allocation flags to use for array expansion
190 * Note that this *copies* the contents of @src into
191 * the array. If you are trying to store an array of
192 * pointers, make sure to pass in &ptr instead of ptr.
193 * You may instead wish to use the flex_array_put_ptr()
196 * Locking must be provided by the caller.
198 int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
202 struct flex_array_part *part;
205 if (element_nr >= fa->total_nr_elements)
207 if (!fa->element_size)
209 if (elements_fit_in_base(fa))
210 part = (struct flex_array_part *)&fa->parts[0];
212 part_nr = fa_element_to_part_nr(fa, element_nr);
213 part = __fa_get_part(fa, part_nr, flags);
217 dst = &part->elements[index_inside_part(fa, element_nr, part_nr)];
218 memcpy(dst, src, fa->element_size);
221 EXPORT_SYMBOL(flex_array_put);
224 * flex_array_clear - clear element in array at @element_nr
225 * @fa: the flex array of the element.
226 * @element_nr: index of the position to clear.
228 * Locking must be provided by the caller.
230 int flex_array_clear(struct flex_array *fa, unsigned int element_nr)
233 struct flex_array_part *part;
236 if (element_nr >= fa->total_nr_elements)
238 if (!fa->element_size)
240 if (elements_fit_in_base(fa))
241 part = (struct flex_array_part *)&fa->parts[0];
243 part_nr = fa_element_to_part_nr(fa, element_nr);
244 part = fa->parts[part_nr];
248 dst = &part->elements[index_inside_part(fa, element_nr, part_nr)];
249 memset(dst, FLEX_ARRAY_FREE, fa->element_size);
252 EXPORT_SYMBOL(flex_array_clear);
255 * flex_array_prealloc - guarantee that array space exists
256 * @fa: the flex array for which to preallocate parts
257 * @start: index of first array element for which space is allocated
258 * @nr_elements: number of elements for which space is allocated
259 * @flags: page allocation flags
261 * This will guarantee that no future calls to flex_array_put()
262 * will allocate memory. It can be used if you are expecting to
263 * be holding a lock or in some atomic context while writing
264 * data into the array.
266 * Locking must be provided by the caller.
268 int flex_array_prealloc(struct flex_array *fa, unsigned int start,
269 unsigned int nr_elements, gfp_t flags)
275 struct flex_array_part *part;
277 if (!start && !nr_elements)
279 if (start >= fa->total_nr_elements)
284 end = start + nr_elements - 1;
286 if (end >= fa->total_nr_elements)
288 if (!fa->element_size)
290 if (elements_fit_in_base(fa))
292 start_part = fa_element_to_part_nr(fa, start);
293 end_part = fa_element_to_part_nr(fa, end);
294 for (part_nr = start_part; part_nr <= end_part; part_nr++) {
295 part = __fa_get_part(fa, part_nr, flags);
301 EXPORT_SYMBOL(flex_array_prealloc);
304 * flex_array_get - pull data back out of the array
305 * @fa: the flex array from which to extract data
306 * @element_nr: index of the element to fetch from the array
308 * Returns a pointer to the data at index @element_nr. Note
309 * that this is a copy of the data that was passed in. If you
310 * are using this to store pointers, you'll get back &ptr. You
311 * may instead wish to use the flex_array_get_ptr helper.
313 * Locking must be provided by the caller.
315 void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
318 struct flex_array_part *part;
320 if (!fa->element_size)
322 if (element_nr >= fa->total_nr_elements)
324 if (elements_fit_in_base(fa))
325 part = (struct flex_array_part *)&fa->parts[0];
327 part_nr = fa_element_to_part_nr(fa, element_nr);
328 part = fa->parts[part_nr];
332 return &part->elements[index_inside_part(fa, element_nr, part_nr)];
334 EXPORT_SYMBOL(flex_array_get);
337 * flex_array_get_ptr - pull a ptr back out of the array
338 * @fa: the flex array from which to extract data
339 * @element_nr: index of the element to fetch from the array
341 * Returns the pointer placed in the flex array at element_nr using
342 * flex_array_put_ptr(). This function should not be called if the
343 * element in question was not set using the _put_ptr() helper.
345 void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr)
349 tmp = flex_array_get(fa, element_nr);
355 EXPORT_SYMBOL(flex_array_get_ptr);
357 static int part_is_free(struct flex_array_part *part)
361 for (i = 0; i < sizeof(struct flex_array_part); i++)
362 if (part->elements[i] != FLEX_ARRAY_FREE)
368 * flex_array_shrink - free unused second-level pages
369 * @fa: the flex array to shrink
371 * Frees all second-level pages that consist solely of unused
372 * elements. Returns the number of pages freed.
374 * Locking must be provided by the caller.
376 int flex_array_shrink(struct flex_array *fa)
378 struct flex_array_part *part;
382 if (!fa->total_nr_elements || !fa->element_size)
384 if (elements_fit_in_base(fa))
386 for (part_nr = 0; part_nr < FLEX_ARRAY_NR_BASE_PTRS; part_nr++) {
387 part = fa->parts[part_nr];
390 if (part_is_free(part)) {
391 fa->parts[part_nr] = NULL;
398 EXPORT_SYMBOL(flex_array_shrink);