xref: /linux/mm/workingset.c (revision 887069f424550ebdcb411166733e1d05002b58e4)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Workingset detection
4  *
5  * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
6  */
7 
8 #include <linux/memcontrol.h>
9 #include <linux/mm_inline.h>
10 #include <linux/writeback.h>
11 #include <linux/shmem_fs.h>
12 #include <linux/pagemap.h>
13 #include <linux/atomic.h>
14 #include <linux/module.h>
15 #include <linux/swap.h>
16 #include <linux/dax.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 
20 /*
21  *		Double CLOCK lists
22  *
23  * Per node, two clock lists are maintained for file pages: the
24  * inactive and the active list.  Freshly faulted pages start out at
25  * the head of the inactive list and page reclaim scans pages from the
26  * tail.  Pages that are accessed multiple times on the inactive list
27  * are promoted to the active list, to protect them from reclaim,
28  * whereas active pages are demoted to the inactive list when the
29  * active list grows too big.
30  *
31  *   fault ------------------------+
32  *                                 |
33  *              +--------------+   |            +-------------+
34  *   reclaim <- |   inactive   | <-+-- demotion |    active   | <--+
35  *              +--------------+                +-------------+    |
36  *                     |                                           |
37  *                     +-------------- promotion ------------------+
38  *
39  *
40  *		Access frequency and refault distance
41  *
42  * A workload is thrashing when its pages are frequently used but they
43  * are evicted from the inactive list every time before another access
44  * would have promoted them to the active list.
45  *
46  * In cases where the average access distance between thrashing pages
47  * is bigger than the size of memory there is nothing that can be
48  * done - the thrashing set could never fit into memory under any
49  * circumstance.
50  *
51  * However, the average access distance could be bigger than the
52  * inactive list, yet smaller than the size of memory.  In this case,
53  * the set could fit into memory if it weren't for the currently
54  * active pages - which may be used more, hopefully less frequently:
55  *
56  *      +-memory available to cache-+
57  *      |                           |
58  *      +-inactive------+-active----+
59  *  a b | c d e f g h i | J K L M N |
60  *      +---------------+-----------+
61  *
62  * It is prohibitively expensive to accurately track access frequency
63  * of pages.  But a reasonable approximation can be made to measure
64  * thrashing on the inactive list, after which refaulting pages can be
65  * activated optimistically to compete with the existing active pages.
66  *
67  * Approximating inactive page access frequency - Observations:
68  *
69  * 1. When a page is accessed for the first time, it is added to the
70  *    head of the inactive list, slides every existing inactive page
71  *    towards the tail by one slot, and pushes the current tail page
72  *    out of memory.
73  *
74  * 2. When a page is accessed for the second time, it is promoted to
75  *    the active list, shrinking the inactive list by one slot.  This
76  *    also slides all inactive pages that were faulted into the cache
77  *    more recently than the activated page towards the tail of the
78  *    inactive list.
79  *
80  * Thus:
81  *
82  * 1. The sum of evictions and activations between any two points in
83  *    time indicate the minimum number of inactive pages accessed in
84  *    between.
85  *
86  * 2. Moving one inactive page N page slots towards the tail of the
87  *    list requires at least N inactive page accesses.
88  *
89  * Combining these:
90  *
91  * 1. When a page is finally evicted from memory, the number of
92  *    inactive pages accessed while the page was in cache is at least
93  *    the number of page slots on the inactive list.
94  *
95  * 2. In addition, measuring the sum of evictions and activations (E)
96  *    at the time of a page's eviction, and comparing it to another
97  *    reading (R) at the time the page faults back into memory tells
98  *    the minimum number of accesses while the page was not cached.
99  *    This is called the refault distance.
100  *
101  * Because the first access of the page was the fault and the second
102  * access the refault, we combine the in-cache distance with the
103  * out-of-cache distance to get the complete minimum access distance
104  * of this page:
105  *
106  *      NR_inactive + (R - E)
107  *
108  * And knowing the minimum access distance of a page, we can easily
109  * tell if the page would be able to stay in cache assuming all page
110  * slots in the cache were available:
111  *
112  *   NR_inactive + (R - E) <= NR_inactive + NR_active
113  *
114  * which can be further simplified to
115  *
116  *   (R - E) <= NR_active
117  *
118  * Put into words, the refault distance (out-of-cache) can be seen as
119  * a deficit in inactive list space (in-cache).  If the inactive list
120  * had (R - E) more page slots, the page would not have been evicted
121  * in between accesses, but activated instead.  And on a full system,
122  * the only thing eating into inactive list space is active pages.
123  *
124  *
125  *		Refaulting inactive pages
126  *
127  * All that is known about the active list is that the pages have been
128  * accessed more than once in the past.  This means that at any given
129  * time there is actually a good chance that pages on the active list
130  * are no longer in active use.
131  *
132  * So when a refault distance of (R - E) is observed and there are at
133  * least (R - E) active pages, the refaulting page is activated
134  * optimistically in the hope that (R - E) active pages are actually
135  * used less frequently than the refaulting page - or even not used at
136  * all anymore.
137  *
138  * That means if inactive cache is refaulting with a suitable refault
139  * distance, we assume the cache workingset is transitioning and put
140  * pressure on the current active list.
141  *
142  * If this is wrong and demotion kicks in, the pages which are truly
143  * used more frequently will be reactivated while the less frequently
144  * used once will be evicted from memory.
145  *
146  * But if this is right, the stale pages will be pushed out of memory
147  * and the used pages get to stay in cache.
148  *
149  *		Refaulting active pages
150  *
151  * If on the other hand the refaulting pages have recently been
152  * deactivated, it means that the active list is no longer protecting
153  * actively used cache from reclaim. The cache is NOT transitioning to
154  * a different workingset; the existing workingset is thrashing in the
155  * space allocated to the page cache.
156  *
157  *
158  *		Implementation
159  *
160  * For each node's LRU lists, a counter for inactive evictions and
161  * activations is maintained (node->nonresident_age).
162  *
163  * On eviction, a snapshot of this counter (along with some bits to
164  * identify the node) is stored in the now empty page cache
165  * slot of the evicted page.  This is called a shadow entry.
166  *
167  * On cache misses for which there are shadow entries, an eligible
168  * refault distance will immediately activate the refaulting page.
169  */
170 
171 #define WORKINGSET_SHIFT 1
172 #define EVICTION_SHIFT	((BITS_PER_LONG - BITS_PER_XA_VALUE) +	\
173 			 WORKINGSET_SHIFT + NODES_SHIFT + \
174 			 MEM_CGROUP_ID_SHIFT)
175 #define EVICTION_MASK	(~0UL >> EVICTION_SHIFT)
176 
177 /*
178  * Eviction timestamps need to be able to cover the full range of
179  * actionable refaults. However, bits are tight in the xarray
180  * entry, and after storing the identifier for the lruvec there might
181  * not be enough left to represent every single actionable refault. In
182  * that case, we have to sacrifice granularity for distance, and group
183  * evictions into coarser buckets by shaving off lower timestamp bits.
184  */
185 static unsigned int bucket_order __read_mostly;
186 
187 static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
188 			 bool workingset)
189 {
190 	eviction >>= bucket_order;
191 	eviction &= EVICTION_MASK;
192 	eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
193 	eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
194 	eviction = (eviction << WORKINGSET_SHIFT) | workingset;
195 
196 	return xa_mk_value(eviction);
197 }
198 
199 static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
200 			  unsigned long *evictionp, bool *workingsetp)
201 {
202 	unsigned long entry = xa_to_value(shadow);
203 	int memcgid, nid;
204 	bool workingset;
205 
206 	workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
207 	entry >>= WORKINGSET_SHIFT;
208 	nid = entry & ((1UL << NODES_SHIFT) - 1);
209 	entry >>= NODES_SHIFT;
210 	memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
211 	entry >>= MEM_CGROUP_ID_SHIFT;
212 
213 	*memcgidp = memcgid;
214 	*pgdat = NODE_DATA(nid);
215 	*evictionp = entry << bucket_order;
216 	*workingsetp = workingset;
217 }
218 
219 /**
220  * workingset_age_nonresident - age non-resident entries as LRU ages
221  * @lruvec: the lruvec that was aged
222  * @nr_pages: the number of pages to count
223  *
224  * As in-memory pages are aged, non-resident pages need to be aged as
225  * well, in order for the refault distances later on to be comparable
226  * to the in-memory dimensions. This function allows reclaim and LRU
227  * operations to drive the non-resident aging along in parallel.
228  */
229 void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages)
230 {
231 	/*
232 	 * Reclaiming a cgroup means reclaiming all its children in a
233 	 * round-robin fashion. That means that each cgroup has an LRU
234 	 * order that is composed of the LRU orders of its child
235 	 * cgroups; and every page has an LRU position not just in the
236 	 * cgroup that owns it, but in all of that group's ancestors.
237 	 *
238 	 * So when the physical inactive list of a leaf cgroup ages,
239 	 * the virtual inactive lists of all its parents, including
240 	 * the root cgroup's, age as well.
241 	 */
242 	do {
243 		atomic_long_add(nr_pages, &lruvec->nonresident_age);
244 	} while ((lruvec = parent_lruvec(lruvec)));
245 }
246 
247 /**
248  * workingset_eviction - note the eviction of a page from memory
249  * @target_memcg: the cgroup that is causing the reclaim
250  * @page: the page being evicted
251  *
252  * Return: a shadow entry to be stored in @page->mapping->i_pages in place
253  * of the evicted @page so that a later refault can be detected.
254  */
255 void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg)
256 {
257 	struct pglist_data *pgdat = page_pgdat(page);
258 	unsigned long eviction;
259 	struct lruvec *lruvec;
260 	int memcgid;
261 
262 	/* Page is fully exclusive and pins page's memory cgroup pointer */
263 	VM_BUG_ON_PAGE(PageLRU(page), page);
264 	VM_BUG_ON_PAGE(page_count(page), page);
265 	VM_BUG_ON_PAGE(!PageLocked(page), page);
266 
267 	lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
268 	/* XXX: target_memcg can be NULL, go through lruvec */
269 	memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
270 	eviction = atomic_long_read(&lruvec->nonresident_age);
271 	workingset_age_nonresident(lruvec, thp_nr_pages(page));
272 	return pack_shadow(memcgid, pgdat, eviction, PageWorkingset(page));
273 }
274 
275 /**
276  * workingset_refault - evaluate the refault of a previously evicted page
277  * @page: the freshly allocated replacement page
278  * @shadow: shadow entry of the evicted page
279  *
280  * Calculates and evaluates the refault distance of the previously
281  * evicted page in the context of the node and the memcg whose memory
282  * pressure caused the eviction.
283  */
284 void workingset_refault(struct page *page, void *shadow)
285 {
286 	bool file = page_is_file_lru(page);
287 	struct mem_cgroup *eviction_memcg;
288 	struct lruvec *eviction_lruvec;
289 	unsigned long refault_distance;
290 	unsigned long workingset_size;
291 	struct pglist_data *pgdat;
292 	struct mem_cgroup *memcg;
293 	unsigned long eviction;
294 	struct lruvec *lruvec;
295 	unsigned long refault;
296 	bool workingset;
297 	int memcgid;
298 
299 	unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
300 
301 	rcu_read_lock();
302 	/*
303 	 * Look up the memcg associated with the stored ID. It might
304 	 * have been deleted since the page's eviction.
305 	 *
306 	 * Note that in rare events the ID could have been recycled
307 	 * for a new cgroup that refaults a shared page. This is
308 	 * impossible to tell from the available data. However, this
309 	 * should be a rare and limited disturbance, and activations
310 	 * are always speculative anyway. Ultimately, it's the aging
311 	 * algorithm's job to shake out the minimum access frequency
312 	 * for the active cache.
313 	 *
314 	 * XXX: On !CONFIG_MEMCG, this will always return NULL; it
315 	 * would be better if the root_mem_cgroup existed in all
316 	 * configurations instead.
317 	 */
318 	eviction_memcg = mem_cgroup_from_id(memcgid);
319 	if (!mem_cgroup_disabled() && !eviction_memcg)
320 		goto out;
321 	eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
322 	refault = atomic_long_read(&eviction_lruvec->nonresident_age);
323 
324 	/*
325 	 * Calculate the refault distance
326 	 *
327 	 * The unsigned subtraction here gives an accurate distance
328 	 * across nonresident_age overflows in most cases. There is a
329 	 * special case: usually, shadow entries have a short lifetime
330 	 * and are either refaulted or reclaimed along with the inode
331 	 * before they get too old.  But it is not impossible for the
332 	 * nonresident_age to lap a shadow entry in the field, which
333 	 * can then result in a false small refault distance, leading
334 	 * to a false activation should this old entry actually
335 	 * refault again.  However, earlier kernels used to deactivate
336 	 * unconditionally with *every* reclaim invocation for the
337 	 * longest time, so the occasional inappropriate activation
338 	 * leading to pressure on the active list is not a problem.
339 	 */
340 	refault_distance = (refault - eviction) & EVICTION_MASK;
341 
342 	/*
343 	 * The activation decision for this page is made at the level
344 	 * where the eviction occurred, as that is where the LRU order
345 	 * during page reclaim is being determined.
346 	 *
347 	 * However, the cgroup that will own the page is the one that
348 	 * is actually experiencing the refault event.
349 	 */
350 	memcg = page_memcg(page);
351 	lruvec = mem_cgroup_lruvec(memcg, pgdat);
352 
353 	inc_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file);
354 
355 	mem_cgroup_flush_stats();
356 	/*
357 	 * Compare the distance to the existing workingset size. We
358 	 * don't activate pages that couldn't stay resident even if
359 	 * all the memory was available to the workingset. Whether
360 	 * workingset competition needs to consider anon or not depends
361 	 * on having swap.
362 	 */
363 	workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
364 	if (!file) {
365 		workingset_size += lruvec_page_state(eviction_lruvec,
366 						     NR_INACTIVE_FILE);
367 	}
368 	if (mem_cgroup_get_nr_swap_pages(memcg) > 0) {
369 		workingset_size += lruvec_page_state(eviction_lruvec,
370 						     NR_ACTIVE_ANON);
371 		if (file) {
372 			workingset_size += lruvec_page_state(eviction_lruvec,
373 						     NR_INACTIVE_ANON);
374 		}
375 	}
376 	if (refault_distance > workingset_size)
377 		goto out;
378 
379 	SetPageActive(page);
380 	workingset_age_nonresident(lruvec, thp_nr_pages(page));
381 	inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file);
382 
383 	/* Page was active prior to eviction */
384 	if (workingset) {
385 		SetPageWorkingset(page);
386 		/* XXX: Move to lru_cache_add() when it supports new vs putback */
387 		lru_note_cost_page(page);
388 		inc_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file);
389 	}
390 out:
391 	rcu_read_unlock();
392 }
393 
394 /**
395  * workingset_activation - note a page activation
396  * @page: page that is being activated
397  */
398 void workingset_activation(struct page *page)
399 {
400 	struct mem_cgroup *memcg;
401 	struct lruvec *lruvec;
402 
403 	rcu_read_lock();
404 	/*
405 	 * Filter non-memcg pages here, e.g. unmap can call
406 	 * mark_page_accessed() on VDSO pages.
407 	 *
408 	 * XXX: See workingset_refault() - this should return
409 	 * root_mem_cgroup even for !CONFIG_MEMCG.
410 	 */
411 	memcg = page_memcg_rcu(page);
412 	if (!mem_cgroup_disabled() && !memcg)
413 		goto out;
414 	lruvec = mem_cgroup_page_lruvec(page);
415 	workingset_age_nonresident(lruvec, thp_nr_pages(page));
416 out:
417 	rcu_read_unlock();
418 }
419 
420 /*
421  * Shadow entries reflect the share of the working set that does not
422  * fit into memory, so their number depends on the access pattern of
423  * the workload.  In most cases, they will refault or get reclaimed
424  * along with the inode, but a (malicious) workload that streams
425  * through files with a total size several times that of available
426  * memory, while preventing the inodes from being reclaimed, can
427  * create excessive amounts of shadow nodes.  To keep a lid on this,
428  * track shadow nodes and reclaim them when they grow way past the
429  * point where they would still be useful.
430  */
431 
432 static struct list_lru shadow_nodes;
433 
434 void workingset_update_node(struct xa_node *node)
435 {
436 	/*
437 	 * Track non-empty nodes that contain only shadow entries;
438 	 * unlink those that contain pages or are being freed.
439 	 *
440 	 * Avoid acquiring the list_lru lock when the nodes are
441 	 * already where they should be. The list_empty() test is safe
442 	 * as node->private_list is protected by the i_pages lock.
443 	 */
444 	VM_WARN_ON_ONCE(!irqs_disabled());  /* For __inc_lruvec_page_state */
445 
446 	if (node->count && node->count == node->nr_values) {
447 		if (list_empty(&node->private_list)) {
448 			list_lru_add(&shadow_nodes, &node->private_list);
449 			__inc_lruvec_kmem_state(node, WORKINGSET_NODES);
450 		}
451 	} else {
452 		if (!list_empty(&node->private_list)) {
453 			list_lru_del(&shadow_nodes, &node->private_list);
454 			__dec_lruvec_kmem_state(node, WORKINGSET_NODES);
455 		}
456 	}
457 }
458 
459 static unsigned long count_shadow_nodes(struct shrinker *shrinker,
460 					struct shrink_control *sc)
461 {
462 	unsigned long max_nodes;
463 	unsigned long nodes;
464 	unsigned long pages;
465 
466 	nodes = list_lru_shrink_count(&shadow_nodes, sc);
467 	if (!nodes)
468 		return SHRINK_EMPTY;
469 
470 	/*
471 	 * Approximate a reasonable limit for the nodes
472 	 * containing shadow entries. We don't need to keep more
473 	 * shadow entries than possible pages on the active list,
474 	 * since refault distances bigger than that are dismissed.
475 	 *
476 	 * The size of the active list converges toward 100% of
477 	 * overall page cache as memory grows, with only a tiny
478 	 * inactive list. Assume the total cache size for that.
479 	 *
480 	 * Nodes might be sparsely populated, with only one shadow
481 	 * entry in the extreme case. Obviously, we cannot keep one
482 	 * node for every eligible shadow entry, so compromise on a
483 	 * worst-case density of 1/8th. Below that, not all eligible
484 	 * refaults can be detected anymore.
485 	 *
486 	 * On 64-bit with 7 xa_nodes per page and 64 slots
487 	 * each, this will reclaim shadow entries when they consume
488 	 * ~1.8% of available memory:
489 	 *
490 	 * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
491 	 */
492 #ifdef CONFIG_MEMCG
493 	if (sc->memcg) {
494 		struct lruvec *lruvec;
495 		int i;
496 
497 		lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
498 		for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
499 			pages += lruvec_page_state_local(lruvec,
500 							 NR_LRU_BASE + i);
501 		pages += lruvec_page_state_local(
502 			lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
503 		pages += lruvec_page_state_local(
504 			lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
505 	} else
506 #endif
507 		pages = node_present_pages(sc->nid);
508 
509 	max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
510 
511 	if (nodes <= max_nodes)
512 		return 0;
513 	return nodes - max_nodes;
514 }
515 
516 static enum lru_status shadow_lru_isolate(struct list_head *item,
517 					  struct list_lru_one *lru,
518 					  spinlock_t *lru_lock,
519 					  void *arg) __must_hold(lru_lock)
520 {
521 	struct xa_node *node = container_of(item, struct xa_node, private_list);
522 	struct address_space *mapping;
523 	int ret;
524 
525 	/*
526 	 * Page cache insertions and deletions synchronously maintain
527 	 * the shadow node LRU under the i_pages lock and the
528 	 * lru_lock.  Because the page cache tree is emptied before
529 	 * the inode can be destroyed, holding the lru_lock pins any
530 	 * address_space that has nodes on the LRU.
531 	 *
532 	 * We can then safely transition to the i_pages lock to
533 	 * pin only the address_space of the particular node we want
534 	 * to reclaim, take the node off-LRU, and drop the lru_lock.
535 	 */
536 
537 	mapping = container_of(node->array, struct address_space, i_pages);
538 
539 	/* Coming from the list, invert the lock order */
540 	if (!xa_trylock(&mapping->i_pages)) {
541 		spin_unlock_irq(lru_lock);
542 		ret = LRU_RETRY;
543 		goto out;
544 	}
545 
546 	list_lru_isolate(lru, item);
547 	__dec_lruvec_kmem_state(node, WORKINGSET_NODES);
548 
549 	spin_unlock(lru_lock);
550 
551 	/*
552 	 * The nodes should only contain one or more shadow entries,
553 	 * no pages, so we expect to be able to remove them all and
554 	 * delete and free the empty node afterwards.
555 	 */
556 	if (WARN_ON_ONCE(!node->nr_values))
557 		goto out_invalid;
558 	if (WARN_ON_ONCE(node->count != node->nr_values))
559 		goto out_invalid;
560 	xa_delete_node(node, workingset_update_node);
561 	__inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
562 
563 out_invalid:
564 	xa_unlock_irq(&mapping->i_pages);
565 	ret = LRU_REMOVED_RETRY;
566 out:
567 	cond_resched();
568 	spin_lock_irq(lru_lock);
569 	return ret;
570 }
571 
572 static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
573 				       struct shrink_control *sc)
574 {
575 	/* list_lru lock nests inside the IRQ-safe i_pages lock */
576 	return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
577 					NULL);
578 }
579 
580 static struct shrinker workingset_shadow_shrinker = {
581 	.count_objects = count_shadow_nodes,
582 	.scan_objects = scan_shadow_nodes,
583 	.seeks = 0, /* ->count reports only fully expendable nodes */
584 	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
585 };
586 
587 /*
588  * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
589  * i_pages lock.
590  */
591 static struct lock_class_key shadow_nodes_key;
592 
593 static int __init workingset_init(void)
594 {
595 	unsigned int timestamp_bits;
596 	unsigned int max_order;
597 	int ret;
598 
599 	BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
600 	/*
601 	 * Calculate the eviction bucket size to cover the longest
602 	 * actionable refault distance, which is currently half of
603 	 * memory (totalram_pages/2). However, memory hotplug may add
604 	 * some more pages at runtime, so keep working with up to
605 	 * double the initial memory by using totalram_pages as-is.
606 	 */
607 	timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
608 	max_order = fls_long(totalram_pages() - 1);
609 	if (max_order > timestamp_bits)
610 		bucket_order = max_order - timestamp_bits;
611 	pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
612 	       timestamp_bits, max_order, bucket_order);
613 
614 	ret = prealloc_shrinker(&workingset_shadow_shrinker);
615 	if (ret)
616 		goto err;
617 	ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
618 			      &workingset_shadow_shrinker);
619 	if (ret)
620 		goto err_list_lru;
621 	register_shrinker_prepared(&workingset_shadow_shrinker);
622 	return 0;
623 err_list_lru:
624 	free_prealloced_shrinker(&workingset_shadow_shrinker);
625 err:
626 	return ret;
627 }
628 module_init(workingset_init);
629