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>
27 struct flex_array_part
{
28 char elements
[FLEX_ARRAY_PART_SIZE
];
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
37 static inline int elements_fit_in_base(struct flex_array
*fa
)
39 int data_size
= fa
->element_size
* fa
->total_nr_elements
;
40 if (data_size
<= FLEX_ARRAY_BASE_BYTES_LEFT
)
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
50 * Note: all locking must be provided by the caller.
52 * @total is used to size internal structures. If the user ever
53 * accesses any array indexes >=@total, it will produce errors.
55 * The maximum number of elements is defined as: the number of
56 * elements that can be stored in a page times the number of
57 * page pointers that we can fit in the base structure or (using
60 * (PAGE_SIZE/element_size) * (PAGE_SIZE-8)/sizeof(void *)
62 * Here's a table showing example capacities. Note that the maximum
63 * index that the get/put() functions is just nr_objects-1. This
64 * basically means that you get 4MB of storage on 32-bit and 2MB on
68 * Element size | Objects | Objects |
69 * PAGE_SIZE=4k | 32-bit | 64-bit |
70 * ---------------------------------|
71 * 1 bytes | 4186112 | 2093056 |
72 * 2 bytes | 2093056 | 1046528 |
73 * 3 bytes | 1395030 | 697515 |
74 * 4 bytes | 1046528 | 523264 |
75 * 32 bytes | 130816 | 65408 |
76 * 33 bytes | 126728 | 63364 |
77 * 2048 bytes | 2044 | 1022 |
78 * 2049 bytes | 1022 | 511 |
79 * void * | 1046528 | 261632 |
81 * Since 64-bit pointers are twice the size, we lose half the
82 * capacity in the base structure. Also note that no effort is made
83 * to efficiently pack objects across page boundaries.
85 struct flex_array
*flex_array_alloc(int element_size
, unsigned int total
,
88 struct flex_array
*ret
;
89 int max_size
= FLEX_ARRAY_NR_BASE_PTRS
*
90 FLEX_ARRAY_ELEMENTS_PER_PART(element_size
);
92 /* max_size will end up 0 if element_size > PAGE_SIZE */
95 ret
= kzalloc(sizeof(struct flex_array
), flags
);
98 ret
->element_size
= element_size
;
99 ret
->total_nr_elements
= total
;
100 if (elements_fit_in_base(ret
) && !(flags
& __GFP_ZERO
))
101 memset(ret
->parts
[0], FLEX_ARRAY_FREE
,
102 FLEX_ARRAY_BASE_BYTES_LEFT
);
106 static int fa_element_to_part_nr(struct flex_array
*fa
,
107 unsigned int element_nr
)
109 return element_nr
/ FLEX_ARRAY_ELEMENTS_PER_PART(fa
->element_size
);
113 * flex_array_free_parts - just free the second-level pages
115 * This is to be used in cases where the base 'struct flex_array'
116 * has been statically allocated and should not be free.
118 void flex_array_free_parts(struct flex_array
*fa
)
122 if (elements_fit_in_base(fa
))
124 for (part_nr
= 0; part_nr
< FLEX_ARRAY_NR_BASE_PTRS
; part_nr
++)
125 kfree(fa
->parts
[part_nr
]);
128 void flex_array_free(struct flex_array
*fa
)
130 flex_array_free_parts(fa
);
134 static unsigned int index_inside_part(struct flex_array
*fa
,
135 unsigned int element_nr
)
137 unsigned int part_offset
;
139 part_offset
= element_nr
%
140 FLEX_ARRAY_ELEMENTS_PER_PART(fa
->element_size
);
141 return part_offset
* fa
->element_size
;
144 static struct flex_array_part
*
145 __fa_get_part(struct flex_array
*fa
, int part_nr
, gfp_t flags
)
147 struct flex_array_part
*part
= fa
->parts
[part_nr
];
149 part
= kmalloc(sizeof(struct flex_array_part
), flags
);
152 if (!(flags
& __GFP_ZERO
))
153 memset(part
, FLEX_ARRAY_FREE
,
154 sizeof(struct flex_array_part
));
155 fa
->parts
[part_nr
] = part
;
161 * flex_array_put - copy data into the array at @element_nr
162 * @src: address of data to copy into the array
163 * @element_nr: index of the position in which to insert
166 * Note that this *copies* the contents of @src into
167 * the array. If you are trying to store an array of
168 * pointers, make sure to pass in &ptr instead of ptr.
170 * Locking must be provided by the caller.
172 int flex_array_put(struct flex_array
*fa
, unsigned int element_nr
, void *src
,
175 int part_nr
= fa_element_to_part_nr(fa
, element_nr
);
176 struct flex_array_part
*part
;
179 if (element_nr
>= fa
->total_nr_elements
)
181 if (elements_fit_in_base(fa
))
182 part
= (struct flex_array_part
*)&fa
->parts
[0];
184 part
= __fa_get_part(fa
, part_nr
, flags
);
188 dst
= &part
->elements
[index_inside_part(fa
, element_nr
)];
189 memcpy(dst
, src
, fa
->element_size
);
194 * flex_array_clear - clear element in array at @element_nr
195 * @element_nr: index of the position to clear.
197 * Locking must be provided by the caller.
199 int flex_array_clear(struct flex_array
*fa
, unsigned int element_nr
)
201 int part_nr
= fa_element_to_part_nr(fa
, element_nr
);
202 struct flex_array_part
*part
;
205 if (element_nr
>= fa
->total_nr_elements
)
207 if (elements_fit_in_base(fa
))
208 part
= (struct flex_array_part
*)&fa
->parts
[0];
210 part
= fa
->parts
[part_nr
];
214 dst
= &part
->elements
[index_inside_part(fa
, element_nr
)];
215 memset(dst
, FLEX_ARRAY_FREE
, fa
->element_size
);
220 * flex_array_prealloc - guarantee that array space exists
221 * @start: index of first array element for which space is allocated
222 * @end: index of last (inclusive) element for which space is allocated
224 * This will guarantee that no future calls to flex_array_put()
225 * will allocate memory. It can be used if you are expecting to
226 * be holding a lock or in some atomic context while writing
227 * data into the array.
229 * Locking must be provided by the caller.
231 int flex_array_prealloc(struct flex_array
*fa
, unsigned int start
,
232 unsigned int end
, gfp_t flags
)
237 struct flex_array_part
*part
;
239 if (start
>= fa
->total_nr_elements
|| end
>= fa
->total_nr_elements
)
241 if (elements_fit_in_base(fa
))
243 start_part
= fa_element_to_part_nr(fa
, start
);
244 end_part
= fa_element_to_part_nr(fa
, end
);
245 for (part_nr
= start_part
; part_nr
<= end_part
; part_nr
++) {
246 part
= __fa_get_part(fa
, part_nr
, flags
);
254 * flex_array_get - pull data back out of the array
255 * @element_nr: index of the element to fetch from the array
257 * Returns a pointer to the data at index @element_nr. Note
258 * that this is a copy of the data that was passed in. If you
259 * are using this to store pointers, you'll get back &ptr.
261 * Locking must be provided by the caller.
263 void *flex_array_get(struct flex_array
*fa
, unsigned int element_nr
)
265 int part_nr
= fa_element_to_part_nr(fa
, element_nr
);
266 struct flex_array_part
*part
;
268 if (element_nr
>= fa
->total_nr_elements
)
270 if (elements_fit_in_base(fa
))
271 part
= (struct flex_array_part
*)&fa
->parts
[0];
273 part
= fa
->parts
[part_nr
];
277 return &part
->elements
[index_inside_part(fa
, element_nr
)];
280 static int part_is_free(struct flex_array_part
*part
)
284 for (i
= 0; i
< sizeof(struct flex_array_part
); i
++)
285 if (part
->elements
[i
] != FLEX_ARRAY_FREE
)
291 * flex_array_shrink - free unused second-level pages
293 * Frees all second-level pages that consist solely of unused
294 * elements. Returns the number of pages freed.
296 * Locking must be provided by the caller.
298 int flex_array_shrink(struct flex_array
*fa
)
300 struct flex_array_part
*part
;
304 if (elements_fit_in_base(fa
))
306 for (part_nr
= 0; part_nr
< FLEX_ARRAY_NR_BASE_PTRS
; part_nr
++) {
307 part
= fa
->parts
[part_nr
];
310 if (part_is_free(part
)) {
311 fa
->parts
[part_nr
] = NULL
;