module/zfs/multilist.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * This file and its contents are supplied under the terms of the
   5  * Common Development and Distribution License ("CDDL"), version 1.0.
   6  * You may only use this file in accordance with the terms of version
   7  * 1.0 of the CDDL.
   8  *
   9  * A full copy of the text of the CDDL should have accompanied this
  10  * source.  A copy of the CDDL is also available via the Internet at
  11  * http://www.illumos.org/license/CDDL.
  12  *
  13  * CDDL HEADER END
  14  */
  15 /*
  16  * Copyright (c) 2013, 2017 by Delphix. All rights reserved.
  17  */
  18
  19 #include <sys/zfs_context.h>
  20 #include <sys/multilist.h>
  21 #include <sys/trace_multilist.h>
  22
  23 /* needed for spa_get_random() */
  24 #include <sys/spa.h>
  25
  26 /*
  27  * This overrides the number of sublists in each multilist_t, which defaults
  28  * to the number of CPUs in the system (see multilist_create()).
  29  */
  30 int zfs_multilist_num_sublists = 0;
  31
  32 /*
  33  * Given the object contained on the list, return a pointer to the
  34  * object's multilist_node_t structure it contains.
  35  */
  36 #ifdef DEBUG
  37 static multilist_node_t *
  38 multilist_d2l(multilist_t *ml, void *obj)
  39 {
  40         return ((multilist_node_t *)((char *)obj + ml->ml_offset));
  41 }
  42 #endif
  43
  44 /*
  45  * Initialize a new mutlilist using the parameters specified.
  46  *
  47  *  - 'size' denotes the size of the structure containing the
  48  *     multilist_node_t.
  49  *  - 'offset' denotes the byte offset of the mutlilist_node_t within
  50  *     the structure that contains it.
  51  *  - 'num' specifies the number of internal sublists to create.
  52  *  - 'index_func' is used to determine which sublist to insert into
  53  *     when the multilist_insert() function is called; as well as which
  54  *     sublist to remove from when multilist_remove() is called. The
  55  *     requirements this function must meet, are the following:
  56  *
  57  *      - It must always return the same value when called on the same
  58  *        object (to ensure the object is removed from the list it was
  59  *        inserted into).
  60  *
  61  *      - It must return a value in the range [0, number of sublists).
  62  *        The multilist_get_num_sublists() function may be used to
  63  *        determine the number of sublists in the multilist.
  64  *
  65  *     Also, in order to reduce internal contention between the sublists
  66  *     during insertion and removal, this function should choose evenly
  67  *     between all available sublists when inserting. This isn't a hard
  68  *     requirement, but a general rule of thumb in order to garner the
  69  *     best multi-threaded performance out of the data structure.
  70  */
  71 static multilist_t *
  72 multilist_create_impl(size_t size, size_t offset,
  73     unsigned int num, multilist_sublist_index_func_t *index_func)
  74 {
  75         ASSERT3U(size, >, 0);
  76         ASSERT3U(size, >=, offset + sizeof (multilist_node_t));
  77         ASSERT3U(num, >, 0);
  78         ASSERT3P(index_func, !=, NULL);
  79
  80         multilist_t *ml = kmem_alloc(sizeof (*ml), KM_SLEEP);
  81         ml->ml_offset = offset;
  82         ml->ml_num_sublists = num;
  83         ml->ml_index_func = index_func;
  84
  85         ml->ml_sublists = kmem_zalloc(sizeof (multilist_sublist_t) *
  86             ml->ml_num_sublists, KM_SLEEP);
  87
  88         ASSERT3P(ml->ml_sublists, !=, NULL);
  89
  90         for (int i = 0; i < ml->ml_num_sublists; i++) {
  91                 multilist_sublist_t *mls = &ml->ml_sublists[i];
  92                 mutex_init(&mls->mls_lock, NULL, MUTEX_NOLOCKDEP, NULL);
  93                 list_create(&mls->mls_list, size, offset);
  94         }
  95         return (ml);
  96 }
  97
  98 /*
  99  * Allocate a new multilist, using the default number of sublists
 100  * (the number of CPUs, or at least 4, or the tunable
 101  * zfs_multilist_num_sublists).
 102  */
 103 multilist_t *
 104 multilist_create(size_t size, size_t offset,
 105     multilist_sublist_index_func_t *index_func)
 106 {
 107         int num_sublists;
 108
 109         if (zfs_multilist_num_sublists > 0) {
 110                 num_sublists = zfs_multilist_num_sublists;
 111         } else {
 112                 num_sublists = MAX(boot_ncpus, 4);
 113         }
 114
 115         return (multilist_create_impl(size, offset, num_sublists, index_func));
 116 }
 117
 118 /*
 119  * Destroy the given multilist object, and free up any memory it holds.
 120  */
 121 void
 122 multilist_destroy(multilist_t *ml)
 123 {
 124         ASSERT(multilist_is_empty(ml));
 125
 126         for (int i = 0; i < ml->ml_num_sublists; i++) {
 127                 multilist_sublist_t *mls = &ml->ml_sublists[i];
 128
 129                 ASSERT(list_is_empty(&mls->mls_list));
 130
 131                 list_destroy(&mls->mls_list);
 132                 mutex_destroy(&mls->mls_lock);
 133         }
 134
 135         ASSERT3P(ml->ml_sublists, !=, NULL);
 136         kmem_free(ml->ml_sublists,
 137             sizeof (multilist_sublist_t) * ml->ml_num_sublists);
 138
 139         ml->ml_num_sublists = 0;
 140         ml->ml_offset = 0;
 141         kmem_free(ml, sizeof (multilist_t));
 142 }
 143
 144 /*
 145  * Insert the given object into the multilist.
 146  *
 147  * This function will insert the object specified into the sublist
 148  * determined using the function given at multilist creation time.
 149  *
 150  * The sublist locks are automatically acquired if not already held, to
 151  * ensure consistency when inserting and removing from multiple threads.
 152  */
 153 void
 154 multilist_insert(multilist_t *ml, void *obj)
 155 {
 156         unsigned int sublist_idx = ml->ml_index_func(ml, obj);
 157         multilist_sublist_t *mls;
 158         boolean_t need_lock;
 159
 160         DTRACE_PROBE3(multilist__insert, multilist_t *, ml,
 161             unsigned int, sublist_idx, void *, obj);
 162
 163         ASSERT3U(sublist_idx, <, ml->ml_num_sublists);
 164
 165         mls = &ml->ml_sublists[sublist_idx];
 166
 167         /*
 168          * Note: Callers may already hold the sublist lock by calling
 169          * multilist_sublist_lock().  Here we rely on MUTEX_HELD()
 170          * returning TRUE if and only if the current thread holds the
 171          * lock.  While it's a little ugly to make the lock recursive in
 172          * this way, it works and allows the calling code to be much
 173          * simpler -- otherwise it would have to pass around a flag
 174          * indicating that it already has the lock.
 175          */
 176         need_lock = !MUTEX_HELD(&mls->mls_lock);
 177
 178         if (need_lock)
 179                 mutex_enter(&mls->mls_lock);
 180
 181         ASSERT(!multilist_link_active(multilist_d2l(ml, obj)));
 182
 183         multilist_sublist_insert_head(mls, obj);
 184
 185         if (need_lock)
 186                 mutex_exit(&mls->mls_lock);
 187 }
 188
 189 /*
 190  * Remove the given object from the multilist.
 191  *
 192  * This function will remove the object specified from the sublist
 193  * determined using the function given at multilist creation time.
 194  *
 195  * The necessary sublist locks are automatically acquired, to ensure
 196  * consistency when inserting and removing from multiple threads.
 197  */
 198 void
 199 multilist_remove(multilist_t *ml, void *obj)
 200 {
 201         unsigned int sublist_idx = ml->ml_index_func(ml, obj);
 202         multilist_sublist_t *mls;
 203         boolean_t need_lock;
 204
 205         DTRACE_PROBE3(multilist__remove, multilist_t *, ml,
 206             unsigned int, sublist_idx, void *, obj);
 207
 208         ASSERT3U(sublist_idx, <, ml->ml_num_sublists);
 209
 210         mls = &ml->ml_sublists[sublist_idx];
 211         /* See comment in multilist_insert(). */
 212         need_lock = !MUTEX_HELD(&mls->mls_lock);
 213
 214         if (need_lock)
 215                 mutex_enter(&mls->mls_lock);
 216
 217         ASSERT(multilist_link_active(multilist_d2l(ml, obj)));
 218
 219         multilist_sublist_remove(mls, obj);
 220
 221         if (need_lock)
 222                 mutex_exit(&mls->mls_lock);
 223 }
 224
 225 /*
 226  * Check to see if this multilist object is empty.
 227  *
 228  * This will return TRUE if it finds all of the sublists of this
 229  * multilist to be empty, and FALSE otherwise. Each sublist lock will be
 230  * automatically acquired as necessary.
 231  *
 232  * If concurrent insertions and removals are occurring, the semantics
 233  * of this function become a little fuzzy. Instead of locking all
 234  * sublists for the entire call time of the function, each sublist is
 235  * only locked as it is individually checked for emptiness. Thus, it's
 236  * possible for this function to return TRUE with non-empty sublists at
 237  * the time the function returns. This would be due to another thread
 238  * inserting into a given sublist, after that specific sublist was check
 239  * and deemed empty, but before all sublists have been checked.
 240  */
 241 int
 242 multilist_is_empty(multilist_t *ml)
 243 {
 244         for (int i = 0; i < ml->ml_num_sublists; i++) {
 245                 multilist_sublist_t *mls = &ml->ml_sublists[i];
 246                 /* See comment in multilist_insert(). */
 247                 boolean_t need_lock = !MUTEX_HELD(&mls->mls_lock);
 248
 249                 if (need_lock)
 250                         mutex_enter(&mls->mls_lock);
 251
 252                 if (!list_is_empty(&mls->mls_list)) {
 253                         if (need_lock)
 254                                 mutex_exit(&mls->mls_lock);
 255
 256                         return (FALSE);
 257                 }
 258
 259                 if (need_lock)
 260                         mutex_exit(&mls->mls_lock);
 261         }
 262
 263         return (TRUE);
 264 }
 265
 266 /* Return the number of sublists composing this multilist */
 267 unsigned int
 268 multilist_get_num_sublists(multilist_t *ml)
 269 {
 270         return (ml->ml_num_sublists);
 271 }
 272
 273 /* Return a randomly selected, valid sublist index for this multilist */
 274 unsigned int
 275 multilist_get_random_index(multilist_t *ml)
 276 {
 277         return (spa_get_random(ml->ml_num_sublists));
 278 }
 279
 280 /* Lock and return the sublist specified at the given index */
 281 multilist_sublist_t *
 282 multilist_sublist_lock(multilist_t *ml, unsigned int sublist_idx)
 283 {
 284         multilist_sublist_t *mls;
 285
 286         ASSERT3U(sublist_idx, <, ml->ml_num_sublists);
 287         mls = &ml->ml_sublists[sublist_idx];
 288         mutex_enter(&mls->mls_lock);
 289
 290         return (mls);
 291 }
 292
 293 /* Lock and return the sublist that would be used to store the specified obj */
 294 multilist_sublist_t *
 295 multilist_sublist_lock_obj(multilist_t *ml, void *obj)
 296 {
 297         return (multilist_sublist_lock(ml, ml->ml_index_func(ml, obj)));
 298 }
 299
 300 void
 301 multilist_sublist_unlock(multilist_sublist_t *mls)
 302 {
 303         mutex_exit(&mls->mls_lock);
 304 }
 305
 306 /*
 307  * We're allowing any object to be inserted into this specific sublist,
 308  * but this can lead to trouble if multilist_remove() is called to
 309  * remove this object. Specifically, if calling ml_index_func on this
 310  * object returns an index for sublist different than what is passed as
 311  * a parameter here, any call to multilist_remove() with this newly
 312  * inserted object is undefined! (the call to multilist_remove() will
 313  * remove the object from a list that it isn't contained in)
 314  */
 315 void
 316 multilist_sublist_insert_head(multilist_sublist_t *mls, void *obj)
 317 {
 318         ASSERT(MUTEX_HELD(&mls->mls_lock));
 319         list_insert_head(&mls->mls_list, obj);
 320 }
 321
 322 /* please see comment above multilist_sublist_insert_head */
 323 void
 324 multilist_sublist_insert_tail(multilist_sublist_t *mls, void *obj)
 325 {
 326         ASSERT(MUTEX_HELD(&mls->mls_lock));
 327         list_insert_tail(&mls->mls_list, obj);
 328 }
 329
 330 /*
 331  * Move the object one element forward in the list.
 332  *
 333  * This function will move the given object forward in the list (towards
 334  * the head) by one object. So, in essence, it will swap its position in
 335  * the list with its "prev" pointer. If the given object is already at the
 336  * head of the list, it cannot be moved forward any more than it already
 337  * is, so no action is taken.
 338  *
 339  * NOTE: This function **must not** remove any object from the list other
 340  *       than the object given as the parameter. This is relied upon in
 341  *       arc_evict_state_impl().
 342  */
 343 void
 344 multilist_sublist_move_forward(multilist_sublist_t *mls, void *obj)
 345 {
 346         void *prev = list_prev(&mls->mls_list, obj);
 347
 348         ASSERT(MUTEX_HELD(&mls->mls_lock));
 349         ASSERT(!list_is_empty(&mls->mls_list));
 350
 351         /* 'obj' must be at the head of the list, nothing to do */
 352         if (prev == NULL)
 353                 return;
 354
 355         list_remove(&mls->mls_list, obj);
 356         list_insert_before(&mls->mls_list, prev, obj);
 357 }
 358
 359 void
 360 multilist_sublist_remove(multilist_sublist_t *mls, void *obj)
 361 {
 362         ASSERT(MUTEX_HELD(&mls->mls_lock));
 363         list_remove(&mls->mls_list, obj);
 364 }
 365
 366 void *
 367 multilist_sublist_head(multilist_sublist_t *mls)
 368 {
 369         ASSERT(MUTEX_HELD(&mls->mls_lock));
 370         return (list_head(&mls->mls_list));
 371 }
 372
 373 void *
 374 multilist_sublist_tail(multilist_sublist_t *mls)
 375 {
 376         ASSERT(MUTEX_HELD(&mls->mls_lock));
 377         return (list_tail(&mls->mls_list));
 378 }
 379
 380 void *
 381 multilist_sublist_next(multilist_sublist_t *mls, void *obj)
 382 {
 383         ASSERT(MUTEX_HELD(&mls->mls_lock));
 384         return (list_next(&mls->mls_list, obj));
 385 }
 386
 387 void *
 388 multilist_sublist_prev(multilist_sublist_t *mls, void *obj)
 389 {
 390         ASSERT(MUTEX_HELD(&mls->mls_lock));
 391         return (list_prev(&mls->mls_list, obj));
 392 }
 393
 394 void
 395 multilist_link_init(multilist_node_t *link)
 396 {
 397         list_link_init(link);
 398 }
 399
 400 int
 401 multilist_link_active(multilist_node_t *link)
 402 {
 403         return (list_link_active(link));
 404 }
 405
 406 #if defined(_KERNEL) && defined(HAVE_SPL)
 407
 408 /* BEGIN CSTYLED */
 409
 410 module_param(zfs_multilist_num_sublists, int, 0644);
 411 MODULE_PARM_DESC(zfs_multilist_num_sublists,
 412         "Number of sublists used in each multilist");
 413
 414 /* END CSTYLED */
 415 #endif