lib/flex_array.c

   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 <dave@linux.vnet.ibm.com>
  21  */
  22
  23 #include <linux/flex_array.h>
  24 #include <linux/slab.h>
  25 #include <linux/stddef.h>
  26
  27 struct 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  */
  37 static 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  */
  86 struct 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
 107 static 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  */
 120 void 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
 130 void flex_array_free(struct flex_array *fa)
 131 {
 132         flex_array_free_parts(fa);
 133         kfree(fa);
 134 }
 135
 136 static 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
 146 static 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  */
 177 int 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  */
 205 int 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  */
 239 int 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  */
 272 void *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
 289 static 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  */
 308 int 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 }