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
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.
16 * Copyright (c) 2013, 2014 by Delphix. All rights reserved.
19 #include <sys/zfs_context.h>
20 #include <sys/multilist.h>
22 /* needed for spa_get_random() */
26 * Given the object contained on the list, return a pointer to the
27 * object's multilist_node_t structure it contains.
29 static multilist_node_t *
30 multilist_d2l(multilist_t *ml, void *obj)
32 return ((multilist_node_t *)((char *)obj + ml->ml_offset));
36 * Initialize a new mutlilist using the parameters specified.
38 * - 'size' denotes the size of the structure containing the
40 * - 'offset' denotes the byte offset of the mutlilist_node_t within
41 * the structure that contains it.
42 * - 'num' specifies the number of internal sublists to create.
43 * - 'index_func' is used to determine which sublist to insert into
44 * when the multilist_insert() function is called; as well as which
45 * sublist to remove from when multilist_remove() is called. The
46 * requirements this function must meet, are the following:
48 * - It must always return the same value when called on the same
49 * object (to ensure the object is removed from the list it was
52 * - It must return a value in the range [0, number of sublists).
53 * The multilist_get_num_sublists() function may be used to
54 * determine the number of sublists in the multilist.
56 * Also, in order to reduce internal contention between the sublists
57 * during insertion and removal, this function should choose evenly
58 * between all available sublists when inserting. This isn't a hard
59 * requirement, but a general rule of thumb in order to garner the
60 * best multi-threaded performance out of the data structure.
63 multilist_create(multilist_t *ml, size_t size, size_t offset, unsigned int num,
64 multilist_sublist_index_func_t *index_func)
66 ASSERT3P(ml, !=, NULL);
68 ASSERT3U(size, >=, offset + sizeof (multilist_node_t));
70 ASSERT3P(index_func, !=, NULL);
72 ml->ml_offset = offset;
73 ml->ml_num_sublists = num;
74 ml->ml_index_func = index_func;
76 ml->ml_sublists = kmem_zalloc(sizeof (multilist_sublist_t) *
77 ml->ml_num_sublists, KM_SLEEP);
79 ASSERT3P(ml->ml_sublists, !=, NULL);
81 for (int i = 0; i < ml->ml_num_sublists; i++) {
82 multilist_sublist_t *mls = &ml->ml_sublists[i];
83 mutex_init(&mls->mls_lock, NULL, MUTEX_DEFAULT, NULL);
84 list_create(&mls->mls_list, size, offset);
89 * Destroy the given multilist object, and free up any memory it holds.
92 multilist_destroy(multilist_t *ml)
94 ASSERT(multilist_is_empty(ml));
96 for (int i = 0; i < ml->ml_num_sublists; i++) {
97 multilist_sublist_t *mls = &ml->ml_sublists[i];
99 ASSERT(list_is_empty(&mls->mls_list));
101 list_destroy(&mls->mls_list);
102 mutex_destroy(&mls->mls_lock);
105 ASSERT3P(ml->ml_sublists, !=, NULL);
106 kmem_free(ml->ml_sublists,
107 sizeof (multilist_sublist_t) * ml->ml_num_sublists);
109 ml->ml_num_sublists = 0;
114 * Insert the given object into the multilist.
116 * This function will insert the object specified into the sublist
117 * determined using the function given at multilist creation time.
119 * The sublist locks are automatically acquired if not already held, to
120 * ensure consistency when inserting and removing from multiple threads.
123 multilist_insert(multilist_t *ml, void *obj)
125 unsigned int sublist_idx = ml->ml_index_func(ml, obj);
126 multilist_sublist_t *mls;
129 DTRACE_PROBE3(multilist__insert, multilist_t *, ml,
130 unsigned int, sublist_idx, void *, obj);
132 ASSERT3U(sublist_idx, <, ml->ml_num_sublists);
134 mls = &ml->ml_sublists[sublist_idx];
137 * Note: Callers may already hold the sublist lock by calling
138 * multilist_sublist_lock(). Here we rely on MUTEX_HELD()
139 * returning TRUE if and only if the current thread holds the
140 * lock. While it's a little ugly to make the lock recursive in
141 * this way, it works and allows the calling code to be much
142 * simpler -- otherwise it would have to pass around a flag
143 * indicating that it already has the lock.
145 need_lock = !MUTEX_HELD(&mls->mls_lock);
148 mutex_enter(&mls->mls_lock);
150 ASSERT(!multilist_link_active(multilist_d2l(ml, obj)));
152 multilist_sublist_insert_head(mls, obj);
155 mutex_exit(&mls->mls_lock);
159 * Remove the given object from the multilist.
161 * This function will remove the object specified from the sublist
162 * determined using the function given at multilist creation time.
164 * The necessary sublist locks are automatically acquired, to ensure
165 * consistency when inserting and removing from multiple threads.
168 multilist_remove(multilist_t *ml, void *obj)
170 unsigned int sublist_idx = ml->ml_index_func(ml, obj);
171 multilist_sublist_t *mls;
174 DTRACE_PROBE3(multilist__remove, multilist_t *, ml,
175 unsigned int, sublist_idx, void *, obj);
177 ASSERT3U(sublist_idx, <, ml->ml_num_sublists);
179 mls = &ml->ml_sublists[sublist_idx];
180 /* See comment in multilist_insert(). */
181 need_lock = !MUTEX_HELD(&mls->mls_lock);
184 mutex_enter(&mls->mls_lock);
186 ASSERT(multilist_link_active(multilist_d2l(ml, obj)));
188 multilist_sublist_remove(mls, obj);
191 mutex_exit(&mls->mls_lock);
195 * Check to see if this multilist object is empty.
197 * This will return TRUE if it finds all of the sublists of this
198 * multilist to be empty, and FALSE otherwise. Each sublist lock will be
199 * automatically acquired as necessary.
201 * If concurrent insertions and removals are occurring, the semantics
202 * of this function become a little fuzzy. Instead of locking all
203 * sublists for the entire call time of the function, each sublist is
204 * only locked as it is individually checked for emptiness. Thus, it's
205 * possible for this function to return TRUE with non-empty sublists at
206 * the time the function returns. This would be due to another thread
207 * inserting into a given sublist, after that specific sublist was check
208 * and deemed empty, but before all sublists have been checked.
211 multilist_is_empty(multilist_t *ml)
213 for (int i = 0; i < ml->ml_num_sublists; i++) {
214 multilist_sublist_t *mls = &ml->ml_sublists[i];
215 /* See comment in multilist_insert(). */
216 boolean_t need_lock = !MUTEX_HELD(&mls->mls_lock);
219 mutex_enter(&mls->mls_lock);
221 if (!list_is_empty(&mls->mls_list)) {
223 mutex_exit(&mls->mls_lock);
229 mutex_exit(&mls->mls_lock);
235 /* Return the number of sublists composing this multilist */
237 multilist_get_num_sublists(multilist_t *ml)
239 return (ml->ml_num_sublists);
242 /* Return a randomly selected, valid sublist index for this multilist */
244 multilist_get_random_index(multilist_t *ml)
246 return (spa_get_random(ml->ml_num_sublists));
249 /* Lock and return the sublist specified at the given index */
250 multilist_sublist_t *
251 multilist_sublist_lock(multilist_t *ml, unsigned int sublist_idx)
253 multilist_sublist_t *mls;
255 ASSERT3U(sublist_idx, <, ml->ml_num_sublists);
256 mls = &ml->ml_sublists[sublist_idx];
257 mutex_enter(&mls->mls_lock);
263 multilist_sublist_unlock(multilist_sublist_t *mls)
265 mutex_exit(&mls->mls_lock);
269 * We're allowing any object to be inserted into this specific sublist,
270 * but this can lead to trouble if multilist_remove() is called to
271 * remove this object. Specifically, if calling ml_index_func on this
272 * object returns an index for sublist different than what is passed as
273 * a parameter here, any call to multilist_remove() with this newly
274 * inserted object is undefined! (the call to multilist_remove() will
275 * remove the object from a list that it isn't contained in)
278 multilist_sublist_insert_head(multilist_sublist_t *mls, void *obj)
280 ASSERT(MUTEX_HELD(&mls->mls_lock));
281 list_insert_head(&mls->mls_list, obj);
284 /* please see comment above multilist_sublist_insert_head */
286 multilist_sublist_insert_tail(multilist_sublist_t *mls, void *obj)
288 ASSERT(MUTEX_HELD(&mls->mls_lock));
289 list_insert_tail(&mls->mls_list, obj);
293 * Move the object one element forward in the list.
295 * This function will move the given object forward in the list (towards
296 * the head) by one object. So, in essence, it will swap its position in
297 * the list with its "prev" pointer. If the given object is already at the
298 * head of the list, it cannot be moved forward any more than it already
299 * is, so no action is taken.
301 * NOTE: This function **must not** remove any object from the list other
302 * than the object given as the parameter. This is relied upon in
303 * arc_evict_state_impl().
306 multilist_sublist_move_forward(multilist_sublist_t *mls, void *obj)
308 void *prev = list_prev(&mls->mls_list, obj);
310 ASSERT(MUTEX_HELD(&mls->mls_lock));
311 ASSERT(!list_is_empty(&mls->mls_list));
313 /* 'obj' must be at the head of the list, nothing to do */
317 list_remove(&mls->mls_list, obj);
318 list_insert_before(&mls->mls_list, prev, obj);
322 multilist_sublist_remove(multilist_sublist_t *mls, void *obj)
324 ASSERT(MUTEX_HELD(&mls->mls_lock));
325 list_remove(&mls->mls_list, obj);
329 multilist_sublist_head(multilist_sublist_t *mls)
331 ASSERT(MUTEX_HELD(&mls->mls_lock));
332 return (list_head(&mls->mls_list));
336 multilist_sublist_tail(multilist_sublist_t *mls)
338 ASSERT(MUTEX_HELD(&mls->mls_lock));
339 return (list_tail(&mls->mls_list));
343 multilist_sublist_next(multilist_sublist_t *mls, void *obj)
345 ASSERT(MUTEX_HELD(&mls->mls_lock));
346 return (list_next(&mls->mls_list, obj));
350 multilist_sublist_prev(multilist_sublist_t *mls, void *obj)
352 ASSERT(MUTEX_HELD(&mls->mls_lock));
353 return (list_prev(&mls->mls_list, obj));
357 multilist_link_init(multilist_node_t *link)
359 list_link_init(link);
363 multilist_link_active(multilist_node_t *link)
365 return (list_link_active(link));